# coding=utf-8
# Copyright 2021 Deepmind and The HuggingFace Inc. team. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
""" PyTorch Perceiver model. """

import abc
import math
from dataclasses import dataclass
from functools import reduce
from operator import __add__
from typing import Any, Callable, Mapping, Optional, Tuple

import numpy as np
import torch
import torch.utils.checkpoint
from torch import nn
from torch.nn import BCEWithLogitsLoss, CrossEntropyLoss, MSELoss

from ...activations import ACT2FN
from ...file_utils import (
    ModelOutput,
    add_code_sample_docstrings,
    add_start_docstrings,
    add_start_docstrings_to_model_forward,
    replace_return_docstrings,
)
from ...modeling_outputs import BaseModelOutputWithCrossAttentions
from ...modeling_utils import (
    PreTrainedModel,
    apply_chunking_to_forward,
    find_pruneable_heads_and_indices,
    prune_linear_layer,
)
from ...utils import logging
from .configuration_perceiver import PerceiverConfig


ModalitySizeType = Mapping[str, int]
PreprocessorOutputType = Tuple[torch.Tensor, Optional[torch.Tensor], torch.Tensor]
PreprocessorType = Callable[..., PreprocessorOutputType]
PostprocessorType = Callable[..., Any]

logger = logging.get_logger(__name__)

_CHECKPOINT_FOR_DOC = "deepmind/language-perceiver"
_CONFIG_FOR_DOC = "PerceiverConfig"
_TOKENIZER_FOR_DOC = "PerceiverTokenizer"

PERCEIVER_PRETRAINED_MODEL_ARCHIVE_LIST = [
    "deepmind/language-perceiver",
    # See all Perceiver models at https://huggingface.co/models?filter=perceiver
]


@dataclass
class PerceiverModelOutput(ModelOutput):
    """
    Base class for Perceiver base model's outputs, with potential hidden states, attentions and cross-attentions.

    Args:
        logits (:obj:`torch.FloatTensor` of shape :obj:`(batch_size, num_labels)`):
            Classification (or regression if config.num_labels==1) scores (before SoftMax).
        last_hidden_state (:obj:`torch.FloatTensor` of shape :obj:`(batch_size, sequence_length, hidden_size)`):
            Sequence of hidden-states at the output of the last layer of the model.
        hidden_states (:obj:`tuple(torch.FloatTensor)`, `optional`, returned when ``output_hidden_states=True`` is passed or when ``config.output_hidden_states=True``):
            Tuple of :obj:`torch.FloatTensor` (one for the output of the embeddings + one for the output of each layer)
            of shape :obj:`(batch_size, sequence_length, hidden_size)`. Hidden-states of the model at the output of
            each layer plus the initial embedding outputs.
        attentions (:obj:`tuple(torch.FloatTensor)`, `optional`, returned when ``output_attentions=True`` is passed or when ``config.output_attentions=True``):
            Tuple of :obj:`torch.FloatTensor` (one for each layer) of shape :obj:`(batch_size, num_heads,
            sequence_length, sequence_length)`. Attentions weights after the attention softmax, used to compute the
            weighted average in the self-attention heads.
        cross_attentions (:obj:`tuple(torch.FloatTensor)`, `optional`, returned when ``output_attentions=True`` is passed or when ``config.output_attentions=True``):
            Tuple of :obj:`torch.FloatTensor` (one for each layer) of shape :obj:`(batch_size, num_heads,
            sequence_length, sequence_length)`. Attentions weights of the decoder's cross-attention layer, after the
            attention softmax, used to compute the weighted average in the cross-attention heads.
    """

    logits: torch.FloatTensor = None
    last_hidden_state: torch.FloatTensor = None
    hidden_states: Optional[Tuple[torch.FloatTensor]] = None
    attentions: Optional[Tuple[torch.FloatTensor]] = None
    cross_attentions: Optional[Tuple[torch.FloatTensor]] = None


@dataclass
class PerceiverDecoderOutput(ModelOutput):
    """
    Base class for Perceiver decoder outputs, with potential cross-attentions.

    Args:
        logits (:obj:`torch.FloatTensor` of shape :obj:`(batch_size, num_labels)`):
            Output of the basic decoder.
        cross_attentions (:obj:`tuple(torch.FloatTensor)`, `optional`, returned when ``output_attentions=True`` is passed or when ``config.output_attentions=True``):
            Tuple of :obj:`torch.FloatTensor` (one for each layer) of shape :obj:`(batch_size, num_heads,
            sequence_length, sequence_length)`. Attentions weights of the decoder's cross-attention layer, after the
            attention softmax, used to compute the weighted average in the cross-attention heads.
    """

    logits: torch.FloatTensor = None
    cross_attentions: Optional[Tuple[torch.FloatTensor]] = None


@dataclass
class PerceiverMaskedLMOutput(ModelOutput):
    """
    Base class for Perceiver's masked language model outputs.

    Args:
        loss (:obj:`torch.FloatTensor` of shape :obj:`(1,)`, `optional`, returned when :obj:`labels` is provided):
            Masked language modeling (MLM) loss.
        logits (:obj:`torch.FloatTensor` of shape :obj:`(batch_size, sequence_length, config.vocab_size)`):
            Prediction scores of the language modeling head (scores for each vocabulary token before SoftMax).
        hidden_states (:obj:`tuple(torch.FloatTensor)`, `optional`, returned when ``output_hidden_states=True`` is passed or when ``config.output_hidden_states=True``):
            Tuple of :obj:`torch.FloatTensor` (one for the output of the embeddings + one for the output of each layer)
            of shape :obj:`(batch_size, sequence_length, hidden_size)`. Hidden-states of the model at the output of
            each layer plus the initial embedding outputs.
        attentions (:obj:`tuple(torch.FloatTensor)`, `optional`, returned when ``output_attentions=True`` is passed or when ``config.output_attentions=True``):
            Tuple of :obj:`torch.FloatTensor` (one for each layer) of shape :obj:`(batch_size, num_heads, num_latents,
            num_latents)`. Attentions weights after the attention softmax, used to compute the weighted average in the
            self-attention heads.
        cross_attentions (:obj:`tuple(torch.FloatTensor)`, `optional`, returned when ``output_attentions=True`` is passed or when ``config.output_attentions=True``):
            Tuple of :obj:`torch.FloatTensor` (one for each layer) of shape :obj:`(batch_size, num_heads,
            sequence_length, sequence_length)`. Attentions weights of the decoder's cross-attention layer, after the
            attention softmax, used to compute the weighted average in the cross-attention heads.
    """

    loss: Optional[torch.FloatTensor] = None
    logits: torch.FloatTensor = None
    hidden_states: Optional[Tuple[torch.FloatTensor]] = None
    attentions: Optional[Tuple[torch.FloatTensor]] = None
    cross_attentions: Optional[Tuple[torch.FloatTensor]] = None


@dataclass
class PerceiverClassifierOutput(ModelOutput):
    """
    Base class for Perceiver's outputs of sequence/image classification models, optical flow and multimodal
    autoencoding.

    Args:
        loss (:obj:`torch.FloatTensor` of shape :obj:`(1,)`, `optional`, returned when :obj:`labels` is provided):
            Classification (or regression if config.num_labels==1) loss.
        logits (:obj:`torch.FloatTensor` of shape :obj:`(batch_size, config.num_labels)`):
            Classification (or regression if config.num_labels==1) scores (before SoftMax).
        hidden_states (:obj:`tuple(torch.FloatTensor)`, `optional`, returned when ``output_hidden_states=True`` is passed or when ``config.output_hidden_states=True``):
            Tuple of :obj:`torch.FloatTensor` (one for the output of the embeddings + one for the output of each layer)
            of shape :obj:`(batch_size, sequence_length, hidden_size)`. Hidden-states of the model at the output of
            each layer plus the initial embedding outputs.
        attentions (:obj:`tuple(torch.FloatTensor)`, `optional`, returned when ``output_attentions=True`` is passed or when ``config.output_attentions=True``):
            Tuple of :obj:`torch.FloatTensor` (one for each layer) of shape :obj:`(batch_size, num_heads,
            sequence_length, sequence_length)`. Attentions weights after the attention softmax, used to compute the
            weighted average in the self-attention heads.
        cross_attentions (:obj:`tuple(torch.FloatTensor)`, `optional`, returned when ``output_attentions=True`` is passed or when ``config.output_attentions=True``):
            Tuple of :obj:`torch.FloatTensor` (one for each layer) of shape :obj:`(batch_size, num_heads,
            sequence_length, sequence_length)`. Attentions weights of the decoder's cross-attention layer, after the
            attention softmax, used to compute the weighted average in the cross-attention heads.
    """

    loss: Optional[torch.FloatTensor] = None
    logits: torch.FloatTensor = None
    hidden_states: Optional[Tuple[torch.FloatTensor]] = None
    attentions: Optional[Tuple[torch.FloatTensor]] = None
    cross_attentions: Optional[Tuple[torch.FloatTensor]] = None


class PerceiverEmbeddings(nn.Module):
    """Construct the latent embeddings."""

    def __init__(self, config):
        super().__init__()
        self.latents = nn.Parameter(torch.randn(config.num_latents, config.d_latents))

    def forward(self, batch_size):
        return self.latents.expand(batch_size, -1, -1)  # Thanks, Phil Wang


class PerceiverSelfAttention(nn.Module):
    """Multi-headed {cross, self}-attention. Can be used both in the encoder as well as in the decoder."""

    def __init__(
        self,
        config,
        is_cross_attention=False,
        qk_channels=None,
        v_channels=None,
        num_heads=1,
        q_dim=None,
        kv_dim=None,
    ):
        super().__init__()
        self.num_heads = num_heads
        # Q and K must have the same number of channels.
        # Default to preserving Q's input's shape.
        if qk_channels is None:
            qk_channels = q_dim
        # V's num_channels determines the shape of the output of QKV-attention.
        # Default to the same number of channels used in the key-query operation.
        if v_channels is None:
            v_channels = qk_channels
        if qk_channels % num_heads != 0:
            raise ValueError(f"qk_channels ({qk_channels}) must be divisible by num_heads ({num_heads}).")
        if v_channels % num_heads != 0:
            raise ValueError(f"v_channels ({v_channels}) must be divisible by num_heads ({num_heads}).")

        self.qk_channels = qk_channels
        self.v_channels = v_channels
        self.qk_channels_per_head = self.qk_channels // num_heads
        self.v_channels_per_head = self.v_channels // num_heads

        # Layer normalization
        self.layernorm1 = nn.LayerNorm(q_dim)
        self.layernorm2 = nn.LayerNorm(kv_dim) if is_cross_attention else nn.Identity()

        # Projection matrices
        self.query = nn.Linear(q_dim, qk_channels)
        self.key = nn.Linear(kv_dim, qk_channels)
        self.value = nn.Linear(kv_dim, v_channels)

        self.dropout = nn.Dropout(config.attention_probs_dropout_prob)

    def transpose_for_scores(self, x, channels_per_head):
        new_x_shape = x.size()[:-1] + (self.num_heads, channels_per_head)
        x = x.view(*new_x_shape)
        return x.permute(0, 2, 1, 3)

    def forward(
        self,
        hidden_states,
        attention_mask=None,
        head_mask=None,
        inputs=None,
        inputs_mask=None,
        output_attentions=False,
    ):
        hidden_states = self.layernorm1(hidden_states)
        inputs = self.layernorm2(inputs)

        # Project queries, keys and values to a common feature dimension. If this is instantiated as a cross-attention module,
        # the keys and values come from the inputs; the attention mask needs to be such that the inputs's non-relevant tokens are not attended to.
        is_cross_attention = inputs is not None
        queries = self.query(hidden_states)

        if is_cross_attention:
            keys = self.key(inputs)
            values = self.value(inputs)
            attention_mask = inputs_mask
        else:
            keys = self.key(hidden_states)
            values = self.value(hidden_states)

        # Reshape channels for multi-head attention.
        # We reshape from (batch_size, time, channels) to (batch_size, num_heads, time, channels per head)
        queries = self.transpose_for_scores(queries, self.qk_channels_per_head)
        keys = self.transpose_for_scores(keys, self.qk_channels_per_head)
        values = self.transpose_for_scores(values, self.v_channels_per_head)

        # Take the dot product between the queries and keys to get the raw attention scores.
        attention_scores = torch.matmul(queries, keys.transpose(-1, -2))

        batch_size, num_heads, seq_len, q_head_dim = queries.shape
        _, _, _, v_head_dim = values.shape
        hiddens = self.num_heads * v_head_dim

        attention_scores = attention_scores / math.sqrt(q_head_dim)

        if attention_mask is not None:
            # Apply the attention mask (precomputed for all layers in PerceiverModel forward() function)
            attention_scores = attention_scores + attention_mask

        # Normalize the attention scores to probabilities.
        attention_probs = nn.Softmax(dim=-1)(attention_scores)

        # This is actually dropping out entire tokens to attend to, which might
        # seem a bit unusual, but is taken from the original Transformer paper.
        attention_probs = self.dropout(attention_probs)

        # Mask heads if we want to
        if head_mask is not None:
            attention_probs = attention_probs * head_mask

        context_layer = torch.matmul(attention_probs, values)

        context_layer = context_layer.permute(0, 2, 1, 3).contiguous()
        new_context_layer_shape = context_layer.size()[:-2] + (hiddens,)
        context_layer = context_layer.view(*new_context_layer_shape)

        outputs = (context_layer, attention_probs) if output_attentions else (context_layer,)

        return outputs


class PerceiverSelfOutput(nn.Module):
    def __init__(self, config, input_channels, output_channels):
        super().__init__()
        self.dense = nn.Linear(input_channels, output_channels)

    def forward(self, hidden_states):
        hidden_states = self.dense(hidden_states)
        return hidden_states


class PerceiverAttention(nn.Module):
    """Attention module, including a dense block."""

    def __init__(
        self,
        config,
        is_cross_attention=False,
        qk_channels=None,
        v_channels=None,
        num_heads=1,
        q_dim=None,
        kv_dim=None,
        use_query_residual=True,
    ):
        super().__init__()
        # MultiHead attention
        if is_cross_attention and qk_channels is None:
            if config.cross_attention_shape_for_attention == "q":
                qk_channels = q_dim
            elif config.cross_attention_shape_for_attention == "kv":
                qk_channels = kv_dim
            else:
                raise ValueError(
                    f"Unknown value {config.cross_attention_shape_for_attention} for "
                    "cross_attention_shape_for_attention."
                )
        else:
            if qk_channels is None:
                qk_channels = q_dim
            if v_channels is None:
                v_channels = qk_channels
        self.self = PerceiverSelfAttention(
            config,
            is_cross_attention=is_cross_attention,
            qk_channels=qk_channels,
            v_channels=v_channels,
            num_heads=num_heads,
            q_dim=q_dim,
            kv_dim=kv_dim,
        )
        # dense block
        output_channels = None
        if is_cross_attention:
            output_channels = q_dim
        else:
            if output_channels is None:
                output_channels = v_channels
        self.output = PerceiverSelfOutput(config, input_channels=self.self.v_channels, output_channels=output_channels)
        self.use_query_residual = use_query_residual
        self.pruned_heads = set()

    def prune_heads(self, heads):
        if len(heads) == 0:
            return
        heads, index = find_pruneable_heads_and_indices(
            heads, self.self.num_attention_heads, self.self.attention_head_size, self.pruned_heads
        )

        # Prune linear layers
        self.self.query = prune_linear_layer(self.self.query, index)
        self.self.key = prune_linear_layer(self.self.key, index)
        self.self.value = prune_linear_layer(self.self.value, index)
        self.output.dense = prune_linear_layer(self.output.dense, index, dim=1)

        # Update hyper params and store pruned heads
        self.self.num_attention_heads = self.self.num_attention_heads - len(heads)
        self.self.all_head_size = self.self.attention_head_size * self.self.num_attention_heads
        self.pruned_heads = self.pruned_heads.union(heads)

    def forward(
        self,
        hidden_states,
        attention_mask=None,
        head_mask=None,
        inputs=None,
        inputs_mask=None,
        output_attentions=False,
    ):
        self_outputs = self.self(
            hidden_states,
            attention_mask,
            head_mask,
            inputs,
            inputs_mask,
            output_attentions,
        )

        # Output projection
        attention_output = self.output(self_outputs[0])

        # Optionally include a residual to the original queries.
        # Consider omitting the residual if the semantics of query and output
        # are different, e.g. if queries are positions and outputs are pixels.
        if self.use_query_residual:
            attention_output = attention_output + hidden_states

        outputs = (attention_output,) + self_outputs[1:]  # add attentions if we output them
        return outputs


class PerceiverMLP(nn.Module):
    """A Transformer-style dense module to follow attention."""

    def __init__(self, config, input_size, widening_factor):
        super().__init__()
        self.dense1 = nn.Linear(input_size, widening_factor * input_size)
        if isinstance(config.hidden_act, str):
            self.intermediate_act_fn = ACT2FN[config.hidden_act]
        else:
            self.intermediate_act_fn = config.hidden_act
        self.dense2 = nn.Linear(input_size, input_size)

    def forward(self, hidden_states):
        hidden_states = self.dense1(hidden_states)
        hidden_states = self.intermediate_act_fn(hidden_states)
        hidden_states = self.dense2(hidden_states)
        return hidden_states


class PerceiverLayer(nn.Module):
    def __init__(
        self,
        config,
        is_cross_attention=False,
        qk_channels=None,
        v_channels=None,
        num_heads=1,
        q_dim=None,
        kv_dim=None,
        widening_factor=4,
        use_query_residual=True,
    ):
        super().__init__()
        self.chunk_size_feed_forward = config.chunk_size_feed_forward
        self.seq_len_dim = 1
        self.attention = PerceiverAttention(
            config,
            is_cross_attention=is_cross_attention,
            qk_channels=qk_channels,
            v_channels=v_channels,
            num_heads=num_heads,
            q_dim=q_dim,
            kv_dim=kv_dim,
            use_query_residual=use_query_residual,
        )
        self.layernorm = nn.LayerNorm(q_dim)
        self.mlp = PerceiverMLP(config, input_size=q_dim, widening_factor=widening_factor)

    def forward(
        self,
        hidden_states,
        attention_mask=None,
        head_mask=None,
        inputs=None,
        inputs_mask=None,
        output_attentions=False,
    ):
        attention_outputs = self.attention(
            hidden_states,
            attention_mask,
            head_mask,
            inputs,
            inputs_mask,
            output_attentions,
        )
        attention_output = attention_outputs[0]

        outputs = attention_outputs[1:]  # add attentions if we output attention weights

        layer_output = apply_chunking_to_forward(
            self.feed_forward_chunk, self.chunk_size_feed_forward, self.seq_len_dim, attention_output
        )

        layer_output = layer_output + attention_output  # residual connection

        outputs = (layer_output,) + outputs

        return outputs

    def feed_forward_chunk(self, attention_output):
        layer_output = self.layernorm(attention_output)
        layer_output = self.mlp(layer_output)
        return layer_output


class PerceiverEncoder(nn.Module):
    """The Perceiver Encoder: a scalable, fully attentional encoder."""

    def __init__(self, config, kv_dim=None):
        super().__init__()
        self.config = config

        # Check that we can use multihead-attention with these shapes.
        if config.d_latents % config.num_self_attention_heads != 0:
            raise ValueError(
                f"num_z_channels ({config.d_latents}) must be divisible by"
                f" num_self_attend_heads ({config.num_self_attention_heads})."
            )
        if config.d_latents % config.num_cross_attention_heads != 0:
            raise ValueError(
                f"num_z_channels ({config.d_latents}) must be divisible by"
                f" num_cross_attend_heads ({config.num_cross_attention_heads})."
            )

        # Construct the cross attention layer.
        self.cross_attention = PerceiverLayer(
            config,
            is_cross_attention=True,
            qk_channels=config.qk_channels,
            v_channels=config.v_channels,
            num_heads=config.num_cross_attention_heads,
            q_dim=config.d_latents,
            kv_dim=kv_dim,
            widening_factor=config.cross_attention_widening_factor,
            use_query_residual=config.use_query_residual,
        )

        # Construct a single block of self-attention layers.
        # We get deeper architectures by applying this block more than once.
        self_attention_layers = []
        for _ in range(config.num_self_attends_per_block):
            layer = PerceiverLayer(
                config,
                is_cross_attention=False,
                qk_channels=config.qk_channels,
                v_channels=config.v_channels,
                num_heads=config.num_self_attention_heads,
                q_dim=config.d_latents,
                kv_dim=config.d_latents,
                widening_factor=config.self_attention_widening_factor,
            )
            self_attention_layers.append(layer)

        self.self_attends = nn.ModuleList(self_attention_layers)

    def forward(
        self,
        hidden_states,
        attention_mask=None,
        head_mask=None,
        inputs=None,
        inputs_mask=None,
        output_attentions=False,
        output_hidden_states=False,
        return_dict=True,
    ):
        all_hidden_states = () if output_hidden_states else None
        all_self_attentions = () if output_attentions else None
        all_cross_attentions = () if output_attentions else None

        # Apply the cross-attention between the latents (hidden_states) and inputs:
        layer_outputs = self.cross_attention(
            hidden_states,
            attention_mask=attention_mask,
            head_mask=None,
            inputs=inputs,
            inputs_mask=inputs_mask,
            output_attentions=output_attentions,
        )
        hidden_states = layer_outputs[0]

        if output_attentions:
            all_cross_attentions = all_cross_attentions + (layer_outputs[1],)

        # Apply the block of self-attention layers more than once:
        for _ in range(self.config.num_blocks):
            for i, layer_module in enumerate(self.self_attends):
                if output_hidden_states:
                    all_hidden_states = all_hidden_states + (hidden_states,)

                layer_head_mask = head_mask[i] if head_mask is not None else None

                layer_outputs = layer_module(
                    hidden_states,
                    attention_mask=attention_mask,
                    head_mask=layer_head_mask,
                    output_attentions=output_attentions,
                )

                hidden_states = layer_outputs[0]
                if output_attentions:
                    all_self_attentions = all_self_attentions + (layer_outputs[1],)

            if output_hidden_states:
                all_hidden_states = all_hidden_states + (hidden_states,)

        if not return_dict:
            return tuple(
                v
                for v in [hidden_states, all_hidden_states, all_self_attentions, all_cross_attentions]
                if v is not None
            )
        return BaseModelOutputWithCrossAttentions(
            last_hidden_state=hidden_states,
            hidden_states=all_hidden_states,
            attentions=all_self_attentions,
            cross_attentions=all_cross_attentions,
        )


class PerceiverPreTrainedModel(PreTrainedModel):
    """
    An abstract class to handle weights initialization and a simple interface for downloading and loading pretrained
    models.
    """

    config_class = PerceiverConfig
    base_model_prefix = "perceiver"

    def _init_weights(self, module):
        """Initialize the weights"""
        if isinstance(module, (nn.Linear, nn.Conv2d)):
            # Slightly different from the TF version which uses truncated_normal for initialization
            # cf https://github.com/pytorch/pytorch/pull/5617
            module.weight.data.normal_(mean=0.0, std=self.config.initializer_range)
            if module.bias is not None:
                module.bias.data.zero_()
        elif hasattr(module, "latents"):
            module.latents.data.normal_(mean=0.0, std=self.config.initializer_range)
        elif hasattr(module, "position_embeddings") and isinstance(module, PerceiverTrainablePositionEncoding):
            module.position_embeddings.data.normal_(mean=0.0, std=self.config.initializer_range)
        elif isinstance(module, nn.ParameterDict):
            for modality in module.keys():
                module[modality].data.normal_(mean=0.0, std=self.config.initializer_range)
        elif isinstance(module, nn.Embedding):
            module.weight.data.normal_(mean=0.0, std=self.config.initializer_range)
            if module.padding_idx is not None:
                module.weight.data[module.padding_idx].zero_()
        elif isinstance(module, nn.LayerNorm):
            module.bias.data.zero_()
            module.weight.data.fill_(1.0)


PERCEIVER_START_DOCSTRING = r"""
    This model is a PyTorch `torch.nn.Module <https://pytorch.org/docs/stable/nn.html#torch.nn.Module>`_ sub-class. Use
    it as a regular PyTorch Module and refer to the PyTorch documentation for all matter related to general usage and
    behavior.

    Parameters:
        config (:class:`~transformers.PerceiverConfig`): Model configuration class with all the parameters of the model.
            Initializing with a config file does not load the weights associated with the model, only the
            configuration. Check out the :meth:`~transformers.PreTrainedModel.from_pretrained` method to load the model
            weights.
"""

PERCEIVER_MODEL_START_DOCSTRING = r"""
    This model is a PyTorch `torch.nn.Module <https://pytorch.org/docs/stable/nn.html#torch.nn.Module>`_ sub-class. Use
    it as a regular PyTorch Module and refer to the PyTorch documentation for all matter related to general usage and
    behavior.

    Parameters:
        config (:class:`~transformers.PerceiverConfig`): Model configuration class with all the parameters of the model.
            Initializing with a config file does not load the weights associated with the model, only the
            configuration. Check out the :meth:`~transformers.PreTrainedModel.from_pretrained` method to load the model
            weights.
        decoder (`DecoderType`, `optional`):
            Optional decoder to use to decode the latent representation of the encoder. Examples include
            `transformers.models.perceiver.modeling_perceiver.PerceiverBasicDecoder`,
            `transformers.models.perceiver.modeling_perceiver.PerceiverClassificationDecoder`,
            `transformers.models.perceiver.modeling_perceiver.PerceiverMultimodalDecoder`.
        input_preprocessor (`PreprocessorType`, `optional`):
            Optional input preprocessor to use. Examples include
            `transformers.models.perceiver.modeling_perceiver.PerceiverImagePreprocessor`,
            `transformers.models.perceiver.modeling_perceiver.PerceiverAudioPreprocessor`,
            `transformers.models.perceiver.modeling_perceiver.PerceiverTextPreprocessor`,
            `transformers.models.perceiver.modeling_perceiver.PerceiverMultimodalPreprocessor`.
        output_postprocessor (`PostprocessorType`, `optional`):
            Optional output postprocessor to use. Examples include
            `transformers.models.perceiver.modeling_perceiver.PerceiverImagePostprocessor`,
            `transformers.models.perceiver.modeling_perceiver.PerceiverAudioPostprocessor`,
            `transformers.models.perceiver.modeling_perceiver.PerceiverClassificationPostprocessor`,
            `transformers.models.perceiver.modeling_perceiver.PerceiverProjectionPostprocessor`,
            `transformers.models.perceiver.modeling_perceiver.PerceiverMultimodalPostprocessor`.

        Note that you can define your own decoders, preprocessors and/or postprocessors to fit your use-case.
"""

PERCEIVER_INPUTS_DOCSTRING = r"""
    Args:
        inputs (:obj:`torch.FloatTensor`):
            Inputs to the perceiver. Can be anything: images, text, audio, video, etc.
        attention_mask (:obj:`torch.FloatTensor` of shape :obj:`{0}`, `optional`):
            Mask to avoid performing attention on padding token indices. Mask values selected in ``[0, 1]``:

            - 1 for tokens that are **not masked**,
            - 0 for tokens that are **masked**.

            `What are attention masks? <../glossary.html#attention-mask>`__
        head_mask (:obj:`torch.FloatTensor` of shape :obj:`(num_heads,)` or :obj:`(num_layers, num_heads)`, `optional`):
            Mask to nullify selected heads of the self-attention modules. Mask values selected in ``[0, 1]``:

            - 1 indicates the head is **not masked**,
            - 0 indicates the head is **masked**.

        output_attentions (:obj:`bool`, `optional`):
            Whether or not to return the attentions tensors of all attention layers. See ``attentions`` under returned
            tensors for more detail.
        output_hidden_states (:obj:`bool`, `optional`):
            Whether or not to return the hidden states of all layers. See ``hidden_states`` under returned tensors for
            more detail.
        return_dict (:obj:`bool`, `optional`):
            Whether or not to return a :class:`~transformers.file_utils.ModelOutput` instead of a plain tuple.
"""


@add_start_docstrings(
    """The Perceiver: a scalable, fully attentional architecture.""",
    PERCEIVER_MODEL_START_DOCSTRING,
)
class PerceiverModel(PerceiverPreTrainedModel):
    def __init__(
        self,
        config,
        decoder=None,
        input_preprocessor: PreprocessorType = None,
        output_postprocessor: PostprocessorType = None,
    ):
        super().__init__(config)
        self.config = config

        self.input_preprocessor = input_preprocessor
        self.output_postprocessor = output_postprocessor
        self.embeddings = PerceiverEmbeddings(config)
        self.encoder = PerceiverEncoder(
            config, kv_dim=input_preprocessor.num_channels if input_preprocessor is not None else config.d_model
        )
        self.decoder = decoder

        # Initialize weights and apply final processing
        self.post_init()

    def get_input_embeddings(self):
        return self.embeddings.latents

    def set_input_embeddings(self, value):
        self.embeddings.latents = value

    def _prune_heads(self, heads_to_prune):
        """
        Prunes heads of the model. heads_to_prune: dict of {layer_num: list of heads to prune in this layer} See base
        class PreTrainedModel
        """
        for layer, heads in heads_to_prune.items():
            self.encoder.layer[layer].attention.prune_heads(heads)

    @add_start_docstrings_to_model_forward(PERCEIVER_INPUTS_DOCSTRING.format("(batch_size, sequence_length)"))
    @replace_return_docstrings(output_type=PerceiverModelOutput, config_class=_CONFIG_FOR_DOC)
    def forward(
        self,
        inputs,
        attention_mask=None,
        subsampled_output_points=None,
        head_mask=None,
        output_attentions=None,
        output_hidden_states=None,
        return_dict=None,
    ):
        r"""
        Returns:

        Examples::

            >>> from transformers import PerceiverConfig, PerceiverTokenizer, PerceiverFeatureExtractor, PerceiverModel
            >>> from transformers.models.perceiver.modeling_perceiver import PerceiverTextPreprocessor, PerceiverImagePreprocessor, PerceiverClassificationDecoder
            >>> import torch
            >>> import requests
            >>> from PIL import Image

            >>> # EXAMPLE 1: using the Perceiver to classify texts
            >>> # - we define a TextPreprocessor, which can be used to embed tokens
            >>> # - we define a ClassificationDecoder, which can be used to decode the
            >>> # final hidden states of the latents to classification logits
            >>> # using trainable position embeddings
            >>> config = PerceiverConfig()
            >>> preprocessor = PerceiverTextPreprocessor(config)
            >>> decoder = PerceiverClassificationDecoder(config,
            ...                                          num_channels=config.d_latents,
            ...                                          trainable_position_encoding_kwargs=dict(num_channels=config.d_latents, index_dims=1),
            ...                                          use_query_residual=True)
            >>> model = PerceiverModel(config, input_preprocessor=preprocessor, decoder=decoder)

            >>> # you can then do a forward pass as follows:
            >>> tokenizer = PerceiverTokenizer()
            >>> text = "hello world"
            >>> inputs = tokenizer(text, return_tensors="pt").input_ids

            >>> with torch.no_grad():
            >>>    outputs = model(inputs=inputs)
            >>> logits = outputs.logits

            >>> # to train, one can train the model using standard cross-entropy:
            >>> criterion = torch.nn.CrossEntropyLoss()

            >>> labels = torch.tensor([1])
            >>> loss = criterion(logits, labels)

            >>> # EXAMPLE 2: using the Perceiver to classify images
            >>> # - we define an ImagePreprocessor, which can be used to embed images
            >>> preprocessor=PerceiverImagePreprocessor(
            ...              config,
            ...              prep_type="conv1x1",
            ...              spatial_downsample=1,
            ...              out_channels=256,
            ...              position_encoding_type="trainable",
            ...              concat_or_add_pos="concat",
            ...              project_pos_dim=256,
            ...              trainable_position_encoding_kwargs=dict(num_channels=256, index_dims=config.image_size ** 2,
            ...              ),
            ... )

            >>> model = PerceiverModel(
            ...         config,
            ...         input_preprocessor=preprocessor,
            ...         decoder=PerceiverClassificationDecoder(
            ...              config,
            ...              num_channels=config.d_latents,
            ...              trainable_position_encoding_kwargs=dict(num_channels=config.d_latents, index_dims=1),
            ...              use_query_residual=True,
            ...          ),
            ... )

            >>> # you can then do a forward pass as follows:
            >>> feature_extractor = PerceiverFeatureExtractor()
            >>> url = 'http://images.cocodataset.org/val2017/000000039769.jpg'
            >>> image = Image.open(requests.get(url, stream=True).raw)
            >>> inputs = feature_extractor(image, return_tensors="pt").pixel_values

            >>> with torch.no_grad():
            >>>    outputs = model(inputs=inputs)
            >>> logits = outputs.logits

            >>> # to train, one can train the model using standard cross-entropy:
            >>> criterion = torch.nn.CrossEntropyLoss()

            >>> labels = torch.tensor([1])
            >>> loss = criterion(logits, labels)
        """
        output_attentions = output_attentions if output_attentions is not None else self.config.output_attentions
        output_hidden_states = (
            output_hidden_states if output_hidden_states is not None else self.config.output_hidden_states
        )
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        if self.input_preprocessor is not None:
            inputs, modality_sizes, inputs_without_pos = self.input_preprocessor(inputs)
        else:
            modality_sizes = None
            inputs_without_pos = None
            if inputs.size()[-1] != self.config.d_model:
                raise ValueError(
                    f"Last dimension of the inputs: {inputs.size()[-1]} doesn't correspond to config.d_model: {self.config.d_model}. "
                    "Make sure to set config.d_model appropriately."
                )

        batch_size, seq_length, _ = inputs.size()
        device = inputs.device

        # If no attention mask is provided, make them all ones
        if attention_mask is None:
            attention_mask = torch.ones(((batch_size, seq_length)), device=device)
        # Make the attention mask broadcastable to [batch_size, num_heads, seq_length, seq_length]
        extended_attention_mask = self.invert_attention_mask(attention_mask)

        # Prepare head mask if needed
        # 1.0 in head_mask indicate we keep the head
        # attention_probs has shape bsz x n_heads x N x N
        # input head_mask has shape [num_heads] or [num_blocks x num_heads]
        # and head_mask is converted to shape [num_blocks x batch x num_heads x N x N]
        head_mask = self.get_head_mask(head_mask, self.config.num_blocks * self.config.num_self_attends_per_block)

        embedding_output = self.embeddings(batch_size=batch_size)

        encoder_outputs = self.encoder(
            embedding_output,
            attention_mask=None,
            head_mask=head_mask,
            inputs=inputs,
            inputs_mask=extended_attention_mask,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )
        sequence_output = encoder_outputs[0]

        logits = None
        if self.decoder:
            if subsampled_output_points is not None:
                output_modality_sizes = {
                    "audio": subsampled_output_points["audio"].shape[0],
                    "image": subsampled_output_points["image"].shape[0],
                    "label": 1,
                }
            else:
                output_modality_sizes = None
            decoder_query = self.decoder.decoder_query(
                inputs, modality_sizes, inputs_without_pos, subsampled_points=subsampled_output_points
            )
            decoder_outputs = self.decoder(
                decoder_query,
                z=sequence_output,
                query_mask=extended_attention_mask,
                output_attentions=output_attentions,
            )
            logits = decoder_outputs.logits

            # add cross-attentions of decoder
            if output_attentions and decoder_outputs.cross_attentions is not None:
                if return_dict:
                    encoder_outputs.cross_attentions = (
                        encoder_outputs.cross_attentions + decoder_outputs.cross_attentions
                    )
                else:
                    encoder_outputs = encoder_outputs + decoder_outputs.cross_attentions

            if self.output_postprocessor:
                logits = self.output_postprocessor(logits, modality_sizes=output_modality_sizes)

        if not return_dict:
            if logits is not None:
                return (logits, sequence_output) + encoder_outputs[1:]
            else:
                return (sequence_output,) + encoder_outputs[1:]

        return PerceiverModelOutput(
            logits=logits,
            last_hidden_state=sequence_output,
            hidden_states=encoder_outputs.hidden_states,
            attentions=encoder_outputs.attentions,
            cross_attentions=encoder_outputs.cross_attentions,
        )


@add_start_docstrings("""Example use of Perceiver for masked language modeling. """, PERCEIVER_START_DOCSTRING)
class PerceiverForMaskedLM(PerceiverPreTrainedModel):
    def __init__(self, config):
        super().__init__(config)

        text_preprocessor = PerceiverTextPreprocessor(config)

        trainable_position_encoding_kwargs_decoder = dict(
            num_channels=text_preprocessor.num_channels, index_dims=config.max_position_embeddings
        )

        self.perceiver = PerceiverModel(
            config,
            input_preprocessor=text_preprocessor,
            decoder=PerceiverBasicDecoder(
                config,
                output_num_channels=config.d_latents,
                output_index_dims=config.max_position_embeddings,  # we need to define the seq_len of the inputs beforehand
                num_channels=text_preprocessor.num_channels,
                qk_channels=8 * 32,
                v_channels=text_preprocessor.num_channels,
                num_heads=8,
                use_query_residual=False,
                final_project=False,
                trainable_position_encoding_kwargs=trainable_position_encoding_kwargs_decoder,
            ),
        )
        self.embedding_decoder = PerceiverEmbeddingDecoder(config)

        # Initialize weights and apply final processing
        self.post_init()

    @add_start_docstrings_to_model_forward(PERCEIVER_INPUTS_DOCSTRING.format("batch_size, sequence_length"))
    @replace_return_docstrings(output_type=PerceiverMaskedLMOutput, config_class=_CONFIG_FOR_DOC)
    def forward(
        self,
        inputs=None,
        attention_mask=None,
        head_mask=None,
        output_attentions=None,
        output_hidden_states=None,
        labels=None,
        return_dict=None,
        input_ids=None,
    ):
        r"""
        labels (:obj:`torch.LongTensor` of shape :obj:`(batch_size, sequence_length)`, `optional`):
            Labels for computing the masked language modeling loss. Indices should be in ``[-100, 0, ...,
            config.vocab_size]`` (see ``input_ids`` docstring) Tokens with indices set to ``-100`` are ignored
            (masked), the loss is only computed for the tokens with labels in ``[0, ..., config.vocab_size]``

        Returns:

        Examples::
            >>> from transformers import PerceiverTokenizer, PerceiverForMaskedLM
            >>> import torch

            >>> tokenizer = PerceiverTokenizer.from_pretrained('deepmind/language-perceiver')
            >>> model = PerceiverForMaskedLM.from_pretrained('deepmind/language-perceiver')

            >>> # training
            >>> text = "This is an incomplete sentence where some words are missing."
            >>> inputs = tokenizer(text, padding="max_length", return_tensors="pt")
            >>> # mask " missing."
            >>> inputs['input_ids'][0, 52:61] = tokenizer.mask_token_id
            >>> labels = tokenizer(text, padding="max_length", return_tensors="pt").input_ids

            >>> outputs = model(**inputs, labels=labels)
            >>> loss = outputs.loss
            >>> logits = outputs.logits

            >>> # inference
            >>> text = "This is an incomplete sentence where some words are missing."
            >>> encoding = tokenizer(text, padding="max_length", return_tensors="pt")

            >>> # mask bytes corresponding to " missing.". Note that the model performs much better if the masked span starts with a space.
            >>> encoding['input_ids'][0, 52:61] = tokenizer.mask_token_id

            >>> # forward pass
            >>> with torch.no_grad():
            >>>    outputs = model(**encoding)
            >>> logits = outputs.logits

            >>> masked_tokens_predictions = logits[0, 52:61].argmax(dim=-1).tolist()
            >>> tokenizer.decode(masked_tokens_predictions)
            ' missing.'
        """
        if inputs is not None and input_ids is not None:
            raise ValueError("You cannot use both `inputs` and `input_ids`")
        elif inputs is None and input_ids is not None:
            inputs = input_ids

        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        outputs = self.perceiver(
            inputs=inputs,
            attention_mask=attention_mask,
            head_mask=head_mask,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )

        logits = self.embedding_decoder(
            outputs.logits if return_dict else outputs[0], embedding_layer=self.perceiver.input_preprocessor.embeddings
        )

        masked_lm_loss = None
        if labels is not None:
            loss_fct = CrossEntropyLoss()  # -100 index = padding token
            masked_lm_loss = loss_fct(logits.view(-1, self.config.vocab_size), labels.view(-1))

        if not return_dict:
            output = (logits,) + outputs[2:]
            return ((masked_lm_loss,) + output) if masked_lm_loss is not None else output

        return PerceiverMaskedLMOutput(
            loss=masked_lm_loss,
            logits=logits,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
            cross_attentions=outputs.cross_attentions,
        )


@add_start_docstrings("""Example use of Perceiver for text classification. """, PERCEIVER_START_DOCSTRING)
class PerceiverForSequenceClassification(PerceiverPreTrainedModel):
    def __init__(self, config):
        super().__init__(config)

        trainable_position_encoding_kwargs_decoder = dict(num_channels=config.d_latents, index_dims=1)

        self.num_labels = config.num_labels
        self.perceiver = PerceiverModel(
            config,
            input_preprocessor=PerceiverTextPreprocessor(config),
            decoder=PerceiverClassificationDecoder(
                config,
                num_channels=config.d_latents,
                trainable_position_encoding_kwargs=trainable_position_encoding_kwargs_decoder,
                use_query_residual=True,
            ),
        )

        # Initialize weights and apply final processing
        self.post_init()

    @add_start_docstrings_to_model_forward(PERCEIVER_INPUTS_DOCSTRING.format("batch_size, sequence_length"))
    @add_code_sample_docstrings(
        processor_class=_TOKENIZER_FOR_DOC,
        checkpoint=_CHECKPOINT_FOR_DOC,
        output_type=PerceiverClassifierOutput,
        config_class=_CONFIG_FOR_DOC,
    )
    def forward(
        self,
        inputs=None,
        attention_mask=None,
        head_mask=None,
        output_attentions=None,
        output_hidden_states=None,
        labels=None,
        return_dict=None,
        input_ids=None,
    ):
        r"""
        labels (:obj:`torch.LongTensor` of shape :obj:`(batch_size,)`, `optional`):
            Labels for computing the classification/regression loss. Indices should be in :obj:`[0, ...,
            config.num_labels - 1]`. If :obj:`config.num_labels == 1` a regression loss is computed (Mean-Square loss),
            If :obj:`config.num_labels > 1` a classification loss is computed (Cross-Entropy).

        Returns:

        Examples::

            >>> from transformers import PerceiverTokenizer, PerceiverForSequenceClassification

            >>> tokenizer = PerceiverTokenizer.from_pretrained('deepmind/language-perceiver')
            >>> model = PerceiverForSequenceClassification.from_pretrained('deepmind/language-perceiver')

            >>> text = "hello world"
            >>> inputs = tokenizer(images=image, return_tensors="pt").input_ids
            >>> outputs = model(inputs=inputs)
            >>> logits = outputs.logits
        """
        if inputs is not None and input_ids is not None:
            raise ValueError("You cannot use both `inputs` and `input_ids`")
        elif inputs is None and input_ids is not None:
            inputs = input_ids

        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        outputs = self.perceiver(
            inputs=inputs,
            attention_mask=attention_mask,
            head_mask=head_mask,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )

        logits = outputs.logits if return_dict else outputs[0]

        loss = None
        if labels is not None:
            if self.config.problem_type is None:
                if self.num_labels == 1:
                    self.config.problem_type = "regression"
                elif self.num_labels > 1 and (labels.dtype == torch.long or labels.dtype == torch.int):
                    self.config.problem_type = "single_label_classification"
                else:
                    self.config.problem_type = "multi_label_classification"

            if self.config.problem_type == "regression":
                loss_fct = MSELoss()
                if self.num_labels == 1:
                    loss = loss_fct(logits.squeeze(), labels.squeeze())
                else:
                    loss = loss_fct(logits, labels)
            elif self.config.problem_type == "single_label_classification":
                loss_fct = CrossEntropyLoss()
                loss = loss_fct(logits.view(-1, self.num_labels), labels.view(-1))
            elif self.config.problem_type == "multi_label_classification":
                loss_fct = BCEWithLogitsLoss()
                loss = loss_fct(logits, labels)

        if not return_dict:
            output = (logits,) + outputs[2:]
            return ((loss,) + output) if loss is not None else output

        return PerceiverClassifierOutput(
            loss=loss,
            logits=logits,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
            cross_attentions=outputs.cross_attentions,
        )


@add_start_docstrings(
    """
Example use of Perceiver for image classification, for tasks such as ImageNet.

This model uses learned position embeddings. In other words, this model is not given any privileged information about
the structure of images. As shown in the paper, this model can achieve a top-1 accuracy of 72.7 on ImageNet.

:class:`~transformers.PerceiverForImageClassificationLearned` uses
:class:`~transformers.models.perceiver.modeling_perceiver.PerceiverImagePreprocessor` (with :obj:`prep_type="conv1x1"`)
to preprocess the input images, and
:class:`~transformers.models.perceiver.modeling_perceiver.PerceiverClassificationDecoder` to decode the latent
representation of :class:`~transformers.PerceiverModel` into classification logits.
""",
    PERCEIVER_START_DOCSTRING,
)
class PerceiverForImageClassificationLearned(PerceiverPreTrainedModel):
    def __init__(self, config):
        super().__init__(config)

        trainable_position_encoding_kwargs_preprocessor = dict(num_channels=256, index_dims=config.image_size ** 2)
        trainable_position_encoding_kwargs_decoder = dict(num_channels=config.d_latents, index_dims=1)

        self.num_labels = config.num_labels
        self.perceiver = PerceiverModel(
            config,
            input_preprocessor=PerceiverImagePreprocessor(
                config,
                prep_type="conv1x1",
                spatial_downsample=1,
                out_channels=256,
                position_encoding_type="trainable",
                concat_or_add_pos="concat",
                project_pos_dim=256,
                trainable_position_encoding_kwargs=trainable_position_encoding_kwargs_preprocessor,
            ),
            decoder=PerceiverClassificationDecoder(
                config,
                num_channels=config.d_latents,
                trainable_position_encoding_kwargs=trainable_position_encoding_kwargs_decoder,
                use_query_residual=True,
            ),
        )

        # Initialize weights and apply final processing
        self.post_init()

    @add_start_docstrings_to_model_forward(PERCEIVER_INPUTS_DOCSTRING.format("batch_size, sequence_length"))
    @replace_return_docstrings(output_type=PerceiverClassifierOutput, config_class=_CONFIG_FOR_DOC)
    def forward(
        self,
        inputs=None,
        attention_mask=None,
        head_mask=None,
        output_attentions=None,
        output_hidden_states=None,
        labels=None,
        return_dict=None,
        pixel_values=None,
    ):
        r"""
        labels (:obj:`torch.LongTensor` of shape :obj:`(batch_size,)`, `optional`):
            Labels for computing the image classification/regression loss. Indices should be in :obj:`[0, ...,
            config.num_labels - 1]`. If :obj:`config.num_labels == 1` a regression loss is computed (Mean-Square loss),
            If :obj:`config.num_labels > 1` a classification loss is computed (Cross-Entropy).

        Returns:

        Examples::

            >>> from transformers import PerceiverFeatureExtractor, PerceiverForImageClassificationLearned
            >>> from PIL import Image
            >>> import requests

            >>> url = 'http://images.cocodataset.org/val2017/000000039769.jpg'
            >>> image = Image.open(requests.get(url, stream=True).raw)

            >>> feature_extractor = PerceiverFeatureExtractor.from_pretrained('deepmind/vision-perceiver-learned')
            >>> model = PerceiverForImageClassificationLearned.from_pretrained('deepmind/vision-perceiver-learned')

            >>> inputs = feature_extractor(images=image, return_tensors="pt").pixel_values
            >>> outputs = model(inputs=inputs)
            >>> logits = outputs.logits
            >>> # model predicts one of the 1000 ImageNet classes
            >>> predicted_class_idx = logits.argmax(-1).item()
            >>> print("Predicted class:", model.config.id2label[predicted_class_idx])
        """
        if inputs is not None and pixel_values is not None:
            raise ValueError("You cannot use both `inputs` and `pixel_values`")
        elif inputs is None and pixel_values is not None:
            inputs = pixel_values

        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        outputs = self.perceiver(
            inputs=inputs,
            attention_mask=attention_mask,
            head_mask=head_mask,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )
        logits = outputs.logits if return_dict else outputs[0]

        loss = None
        if labels is not None:
            if self.config.problem_type is None:
                if self.num_labels == 1:
                    self.config.problem_type = "regression"
                elif self.num_labels > 1 and (labels.dtype == torch.long or labels.dtype == torch.int):
                    self.config.problem_type = "single_label_classification"
                else:
                    self.config.problem_type = "multi_label_classification"

            if self.config.problem_type == "regression":
                loss_fct = MSELoss()
                if self.num_labels == 1:
                    loss = loss_fct(logits.squeeze(), labels.squeeze())
                else:
                    loss = loss_fct(logits, labels)
            elif self.config.problem_type == "single_label_classification":
                loss_fct = CrossEntropyLoss()
                loss = loss_fct(logits.view(-1, self.num_labels), labels.view(-1))
            elif self.config.problem_type == "multi_label_classification":
                loss_fct = BCEWithLogitsLoss()
                loss = loss_fct(logits, labels)

        if not return_dict:
            output = (logits,) + outputs[2:]
            return ((loss,) + output) if loss is not None else output

        return PerceiverClassifierOutput(
            loss=loss,
            logits=logits,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
            cross_attentions=outputs.cross_attentions,
        )


@add_start_docstrings(
    """
Example use of Perceiver for image classification, for tasks such as ImageNet.

This model uses fixed 2D Fourier position embeddings. As shown in the paper, this model can achieve a top-1 accuracy of
79.0 on ImageNet, and 84.5 when pre-trained on a large-scale dataset (i.e. JFT).

:class:`~transformers.PerceiverForImageClassificationLearned` uses
:class:`~transformers.models.perceiver.modeling_perceiver.PerceiverImagePreprocessor` (with :obj:`prep_type="pixels"`)
to preprocess the input images, and
:class:`~transformers.models.perceiver.modeling_perceiver.PerceiverClassificationDecoder` to decode the latent
representation of :class:`~transformers.PerceiverModel` into classification logits.
""",
    PERCEIVER_START_DOCSTRING,
)
class PerceiverForImageClassificationFourier(PerceiverPreTrainedModel):
    def __init__(self, config):
        super().__init__(config)

        fourier_position_encoding_kwargs_preprocessor = dict(
            concat_pos=True, max_resolution=(224, 224), num_bands=64, sine_only=False
        )
        trainable_position_encoding_kwargs_decoder = dict(num_channels=config.d_latents, index_dims=1)

        self.num_labels = config.num_labels
        self.perceiver = PerceiverModel(
            config,
            input_preprocessor=PerceiverImagePreprocessor(
                config,
                prep_type="pixels",
                spatial_downsample=1,
                fourier_position_encoding_kwargs=fourier_position_encoding_kwargs_preprocessor,
            ),
            decoder=PerceiverClassificationDecoder(
                config,
                num_channels=config.d_latents,
                trainable_position_encoding_kwargs=trainable_position_encoding_kwargs_decoder,
                use_query_residual=True,
            ),
        )

        # Initialize weights and apply final processing
        self.post_init()

    @add_start_docstrings_to_model_forward(PERCEIVER_INPUTS_DOCSTRING.format("batch_size, sequence_length"))
    @replace_return_docstrings(output_type=PerceiverClassifierOutput, config_class=_CONFIG_FOR_DOC)
    def forward(
        self,
        inputs=None,
        attention_mask=None,
        head_mask=None,
        output_attentions=None,
        output_hidden_states=None,
        labels=None,
        return_dict=None,
        pixel_values=None,
    ):
        r"""
        labels (:obj:`torch.LongTensor` of shape :obj:`(batch_size,)`, `optional`):
            Labels for computing the image classification/regression loss. Indices should be in :obj:`[0, ...,
            config.num_labels - 1]`. If :obj:`config.num_labels == 1` a regression loss is computed (Mean-Square loss),
            If :obj:`config.num_labels > 1` a classification loss is computed (Cross-Entropy).

        Returns:

        Examples::

            >>> from transformers import PerceiverFeatureExtractor, PerceiverForImageClassificationFourier
            >>> from PIL import Image
            >>> import requests

            >>> url = 'http://images.cocodataset.org/val2017/000000039769.jpg'
            >>> image = Image.open(requests.get(url, stream=True).raw)

            >>> feature_extractor = PerceiverFeatureExtractor.from_pretrained('deepmind/vision-perceiver-fourier')
            >>> model = PerceiverForImageClassificationFourier.from_pretrained('deepmind/vision-perceiver-fourier')

            >>> inputs = feature_extractor(images=image, return_tensors="pt").pixel_values
            >>> outputs = model(inputs=inputs)
            >>> logits = outputs.logits
            >>> # model predicts one of the 1000 ImageNet classes
            >>> predicted_class_idx = logits.argmax(-1).item()
            >>> print("Predicted class:", model.config.id2label[predicted_class_idx])
        """
        if inputs is not None and pixel_values is not None:
            raise ValueError("You cannot use both `inputs` and `pixel_values`")
        elif inputs is None and pixel_values is not None:
            inputs = pixel_values
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        outputs = self.perceiver(
            inputs=inputs,
            attention_mask=attention_mask,
            head_mask=head_mask,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )
        logits = outputs.logits if return_dict else outputs[0]

        loss = None
        if labels is not None:
            if self.config.problem_type is None:
                if self.num_labels == 1:
                    self.config.problem_type = "regression"
                elif self.num_labels > 1 and (labels.dtype == torch.long or labels.dtype == torch.int):
                    self.config.problem_type = "single_label_classification"
                else:
                    self.config.problem_type = "multi_label_classification"

            if self.config.problem_type == "regression":
                loss_fct = MSELoss()
                if self.num_labels == 1:
                    loss = loss_fct(logits.squeeze(), labels.squeeze())
                else:
                    loss = loss_fct(logits, labels)
            elif self.config.problem_type == "single_label_classification":
                loss_fct = CrossEntropyLoss()
                loss = loss_fct(logits.view(-1, self.num_labels), labels.view(-1))
            elif self.config.problem_type == "multi_label_classification":
                loss_fct = BCEWithLogitsLoss()
                loss = loss_fct(logits, labels)

        if not return_dict:
            output = (logits,) + outputs[2:]
            return ((loss,) + output) if loss is not None else output

        return PerceiverClassifierOutput(
            loss=loss,
            logits=logits,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
            cross_attentions=outputs.cross_attentions,
        )


@add_start_docstrings(
    """
Example use of Perceiver for image classification, for tasks such as ImageNet.

This model uses a 2D conv+maxpool preprocessing network. As shown in the paper, this model can achieve a top-1 accuracy
of 82.1 on ImageNet.

:class:`~transformers.PerceiverForImageClassificationLearned` uses
:class:`~transformers.models.perceiver.modeling_perceiver.PerceiverImagePreprocessor` (with :obj:`prep_type="conv"`) to
preprocess the input images, and
:class:`~transformers.models.perceiver.modeling_perceiver.PerceiverClassificationDecoder` to decode the latent
representation of :class:`~transformers.PerceiverModel` into classification logits.
""",
    PERCEIVER_START_DOCSTRING,
)
class PerceiverForImageClassificationConvProcessing(PerceiverPreTrainedModel):
    def __init__(self, config):
        super().__init__(config)

        fourier_position_encoding_kwargs_preprocessor = dict(
            concat_pos=True, max_resolution=(56, 56), num_bands=64, sine_only=False
        )
        trainable_position_encoding_kwargs_decoder = dict(num_channels=config.d_latents, index_dims=1)

        self.num_labels = config.num_labels
        self.perceiver = PerceiverModel(
            config,
            input_preprocessor=PerceiverImagePreprocessor(
                config,
                prep_type="conv",
                spatial_downsample=1,
                position_encoding_type="fourier",
                fourier_position_encoding_kwargs=fourier_position_encoding_kwargs_preprocessor,
            ),
            decoder=PerceiverClassificationDecoder(
                config,
                num_channels=config.d_latents,
                trainable_position_encoding_kwargs=trainable_position_encoding_kwargs_decoder,
                use_query_residual=True,
            ),
        )

        # Initialize weights and apply final processing
        self.post_init()

    @add_start_docstrings_to_model_forward(PERCEIVER_INPUTS_DOCSTRING.format("batch_size, sequence_length"))
    @replace_return_docstrings(output_type=PerceiverClassifierOutput, config_class=_CONFIG_FOR_DOC)
    def forward(
        self,
        inputs=None,
        attention_mask=None,
        head_mask=None,
        output_attentions=None,
        output_hidden_states=None,
        labels=None,
        return_dict=None,
        pixel_values=None,
    ):
        r"""
        labels (:obj:`torch.LongTensor` of shape :obj:`(batch_size,)`, `optional`):
            Labels for computing the image classification/regression loss. Indices should be in :obj:`[0, ...,
            config.num_labels - 1]`. If :obj:`config.num_labels == 1` a regression loss is computed (Mean-Square loss),
            If :obj:`config.num_labels > 1` a classification loss is computed (Cross-Entropy).

        Returns:

        Examples::

            >>> from transformers import PerceiverFeatureExtractor, PerceiverForImageClassificationConvProcessing
            >>> from PIL import Image
            >>> import requests

            >>> url = 'http://images.cocodataset.org/val2017/000000039769.jpg'
            >>> image = Image.open(requests.get(url, stream=True).raw)

            >>> feature_extractor = PerceiverFeatureExtractor.from_pretrained('deepmind/vision-perceiver-conv')
            >>> model = PerceiverForImageClassificationConvProcessing.from_pretrained('deepmind/vision-perceiver-conv')

            >>> inputs = feature_extractor(images=image, return_tensors="pt").pixel_values
            >>> outputs = model(inputs=inputs)
            >>> logits = outputs.logits
            >>> # model predicts one of the 1000 ImageNet classes
            >>> predicted_class_idx = logits.argmax(-1).item()
            >>> print("Predicted class:", model.config.id2label[predicted_class_idx])
        """
        if inputs is not None and pixel_values is not None:
            raise ValueError("You cannot use both `inputs` and `pixel_values`")
        elif inputs is None and pixel_values is not None:
            inputs = pixel_values
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        outputs = self.perceiver(
            inputs=inputs,
            attention_mask=attention_mask,
            head_mask=head_mask,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )
        logits = outputs.logits if return_dict else outputs[0]

        loss = None
        if labels is not None:
            if self.config.problem_type is None:
                if self.num_labels == 1:
                    self.config.problem_type = "regression"
                elif self.num_labels > 1 and (labels.dtype == torch.long or labels.dtype == torch.int):
                    self.config.problem_type = "single_label_classification"
                else:
                    self.config.problem_type = "multi_label_classification"

            if self.config.problem_type == "regression":
                loss_fct = MSELoss()
                if self.num_labels == 1:
                    loss = loss_fct(logits.squeeze(), labels.squeeze())
                else:
                    loss = loss_fct(logits, labels)
            elif self.config.problem_type == "single_label_classification":
                loss_fct = CrossEntropyLoss()
                loss = loss_fct(logits.view(-1, self.num_labels), labels.view(-1))
            elif self.config.problem_type == "multi_label_classification":
                loss_fct = BCEWithLogitsLoss()
                loss = loss_fct(logits, labels)

        if not return_dict:
            output = (logits,) + outputs[2:]
            return ((loss,) + output) if loss is not None else output

        return PerceiverClassifierOutput(
            loss=loss,
            logits=logits,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
            cross_attentions=outputs.cross_attentions,
        )


@add_start_docstrings(
    """
Example use of Perceiver for optical flow, for tasks such as Sintel and KITTI.
:class:`~transformers.PerceiverForOpticalFlow` uses
:class:`~transformers.models.perceiver.modeling_perceiver.PerceiverImagePreprocessor` (with `prep_type="patches"`) to
preprocess the input images, and :class:`~transformers.models.perceiver.modeling_perceiver.PerceiverOpticalFlowDecoder`
to decode the latent representation of :class:`~transformers.PerceiverModel`.

As input, one concatenates 2 subsequent frames along the channel dimension and extract a 3 x 3 patch around each pixel
(leading to 3 x 3 x 3 x 2 = 54 values for each pixel). Fixed Fourier position encodings are used to encode the position
of each pixel in the patch. Next, one applies the Perceiver encoder. To decode, one queries the latent representation
using the same encoding used for the input.
""",
    PERCEIVER_START_DOCSTRING,
)
class PerceiverForOpticalFlow(PerceiverPreTrainedModel):
    def __init__(self, config):
        super().__init__(config)

        fourier_position_encoding_kwargs_preprocessor = dict(
            num_bands=64,
            max_resolution=config.train_size,
            sine_only=False,
            concat_pos=True,
        )
        fourier_position_encoding_kwargs_decoder = dict(
            concat_pos=True, max_resolution=config.train_size, num_bands=64, sine_only=False
        )

        image_preprocessor = PerceiverImagePreprocessor(
            config,
            prep_type="patches",
            spatial_downsample=1,
            conv_after_patching=True,
            conv_after_patching_in_channels=54,
            temporal_downsample=2,
            position_encoding_type="fourier",
            # position_encoding_kwargs
            fourier_position_encoding_kwargs=fourier_position_encoding_kwargs_preprocessor,
        )

        self.perceiver = PerceiverModel(
            config,
            input_preprocessor=image_preprocessor,
            decoder=PerceiverOpticalFlowDecoder(
                config,
                num_channels=image_preprocessor.num_channels,
                output_image_shape=config.train_size,
                rescale_factor=100.0,
                # decoder kwargs
                use_query_residual=False,
                output_num_channels=2,
                # We query the decoder using the first frame features
                # rather than a standard decoder position encoding.
                position_encoding_type="fourier",
                fourier_position_encoding_kwargs=fourier_position_encoding_kwargs_decoder,
            ),
        )

        # Initialize weights and apply final processing
        self.post_init()

    @add_start_docstrings_to_model_forward(PERCEIVER_INPUTS_DOCSTRING.format("batch_size, sequence_length"))
    @replace_return_docstrings(output_type=PerceiverClassifierOutput, config_class=_CONFIG_FOR_DOC)
    def forward(
        self,
        inputs=None,
        attention_mask=None,
        head_mask=None,
        output_attentions=None,
        output_hidden_states=None,
        labels=None,
        return_dict=None,
    ):
        r"""
        labels (:obj:`torch.LongTensor` of shape :obj:`(batch_size,)`, `optional`):
            Labels for computing the optical flow loss. Indices should be in :obj:`[0, ..., config.num_labels - 1]`.

        Returns:

        Examples::

            >>> from transformers import PerceiverForOpticalFlow
            >>> import torch

            >>> model = PerceiverForOpticalFlow.from_pretrained('deepmind/optical-flow-perceiver')

            >>> # in the Perceiver IO paper, the authors extract a 3 x 3 patch around each pixel,
            >>> # leading to 3 x 3 x 3 = 27 values for each pixel (as each pixel also has 3 color channels)
            >>> # patches have shape (batch_size, num_frames, num_channels, height, width)
            >>> # the authors train on resolutions of 368 x 496
            >>> patches = torch.randn(1, 2, 27, 368, 496)
            >>> outputs = model(inputs=patches)
            >>> logits = outputs.logits
        """
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        outputs = self.perceiver(
            inputs=inputs,
            attention_mask=attention_mask,
            head_mask=head_mask,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )
        logits = outputs.logits if return_dict else outputs[0]

        loss = None
        if labels is not None:
            raise NotImplementedError("Optical flow training is not yet supported")

        if not return_dict:
            output = (logits,) + outputs[2:]
            return ((loss,) + output) if loss is not None else output

        return PerceiverClassifierOutput(
            loss=loss,
            logits=logits,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
            cross_attentions=outputs.cross_attentions,
        )


@add_start_docstrings(
    """
Example use of Perceiver for multimodal (video) autoencoding, for tasks such as Kinetics-700.

:class:`~transformers.PerceiverForMultimodalAutoencoding` uses
:class:`~transformers.models.perceiver.modeling_perceiver.PerceiverMultimodalPreprocessor` to preprocess the 3
modalities: images, audio and class labels. This preprocessor uses modality-specific preprocessors to preprocess every
modality separately, after which they are concatenated. Trainable position embeddings are used to pad each modality to
the same number of channels to make concatenation along the time dimension possible. Next, one applies the Perceiver
encoder.

:class:`~transformers.models.perceiver.modeling_perceiver.PerceiverMultimodalDecoder` is used to decode the latent
representation of :class:`~transformers.PerceiverModel`. This decoder uses each modality-specific decoder to construct
queries. The decoder queries are created based on the inputs after preprocessing. However, autoencoding an entire video
in a single forward pass is computationally infeasible, hence one only uses parts of the decoder queries to do
cross-attention with the latent representation. This is determined by the subsampled indices for each modality, which
can be provided as additional input to the forward pass of :class:`~transformers.PerceiverForMultimodalAutoencoding`.

:class:`~transformers.models.perceiver.modeling_perceiver.PerceiverMultimodalDecoder` also pads the decoder queries of
the different modalities to the same number of channels, in order to concatenate them along the time dimension. Next,
cross-attention is performed with the latent representation of :class:`~transformers.PerceiverModel`.

Finally, :class:`~transformers.models.perceiver.modeling_perceiver.PerceiverMultiModalPostprocessor` is used to turn
this tensor into an actual video. It first splits up the output into the different modalities, and then applies the
respective postprocessor for each modality.

Note that, by masking the classification label during evaluation (i.e. simply providing a tensor of zeros for the
"label" modality), this auto-encoding model becomes a Kinetics 700 video classifier.
""",
    PERCEIVER_START_DOCSTRING,
)
class PerceiverForMultimodalAutoencoding(PerceiverPreTrainedModel):
    def __init__(self, config):
        super().__init__(config)

        n_audio_samples = config.num_frames * config.audio_samples_per_frame

        input_preprocessor = PerceiverMultimodalPreprocessor(
            min_padding_size=4,
            modalities={
                "audio": PerceiverAudioPreprocessor(
                    config,
                    position_encoding_type="fourier",
                    fourier_position_encoding_kwargs=dict(
                        num_bands=192,
                        max_resolution=(n_audio_samples,),
                        sine_only=False,
                        concat_pos=True,
                    ),
                    prep_type="patches",
                    samples_per_patch=config.samples_per_patch,
                ),
                "image": PerceiverImagePreprocessor(
                    config,
                    position_encoding_type="fourier",
                    fourier_position_encoding_kwargs=dict(
                        num_bands=32,
                        max_resolution=(config.num_frames, config.image_size, config.image_size),
                        sine_only=False,
                        concat_pos=True,
                    ),
                    prep_type="patches",
                    spatial_downsample=4,
                    temporal_downsample=1,
                ),
                "label": PerceiverOneHotPreprocessor(config),
            },
            mask_probs={"image": 0.0, "audio": 0.0, "label": 1.0},
        )

        image_decoder = PerceiverBasicVideoAutoencodingDecoder(
            config,
            # Autoencoding, don't pass inputs to the queries.
            concat_preprocessed_input=False,
            output_shape=config.output_shape,
            output_num_channels=512,
            use_query_residual=False,
            position_encoding_only=True,
            position_encoding_type="fourier",
            fourier_position_encoding_kwargs=dict(
                num_bands=32,
                max_resolution=(config.num_frames, config.image_size, config.image_size),
                sine_only=False,
                concat_pos=True,
            ),
        )

        decoder = PerceiverMultimodalDecoder(
            config,
            # Autoencoding, don't pass inputs to the queries.
            concat_preprocessed_input=False,
            # Modality specific decoders are used ONLY to generate queries.
            # All modalties are decoded together using a unified decoder.
            modalities={
                "audio": PerceiverBasicDecoder(
                    config,
                    # Autoencoding, don't pass inputs to the queries.
                    concat_preprocessed_input=False,
                    output_index_dims=(n_audio_samples // config.samples_per_patch,),
                    output_num_channels=512,
                    use_query_residual=False,
                    position_encoding_only=True,
                    position_encoding_type="fourier",
                    fourier_position_encoding_kwargs=dict(
                        num_bands=192,
                        max_resolution=(n_audio_samples,),
                        sine_only=False,
                        concat_pos=True,
                    ),
                ),
                "image": image_decoder,
                "label": PerceiverClassificationDecoder(
                    config,
                    # Autoencoding, don't pass inputs to the queries.
                    concat_preprocessed_input=False,
                    use_query_residual=False,
                    position_encoding_only=True,
                    position_encoding_type="trainable",
                    trainable_position_encoding_kwargs=dict(
                        num_channels=1024,
                        index_dims=1,
                    ),
                ),
            },
            num_outputs=None,
            output_num_channels=512,
            use_query_residual=False,
        )

        output_postprocessor = PerceiverMultimodalPostprocessor(
            modalities={
                "audio": PerceiverAudioPostprocessor(config, in_channels=512),
                "image": PerceiverProjectionPostprocessor(in_channels=512, out_channels=3),
                "label": PerceiverClassificationPostprocessor(config, in_channels=512),
            }
        )

        self.perceiver = PerceiverModel(
            config,
            input_preprocessor=input_preprocessor,
            decoder=decoder,
            output_postprocessor=output_postprocessor,
        )

        # Initialize weights and apply final processing
        self.post_init()

    @add_start_docstrings_to_model_forward(PERCEIVER_INPUTS_DOCSTRING.format("batch_size, sequence_length"))
    @replace_return_docstrings(output_type=PerceiverClassifierOutput, config_class=_CONFIG_FOR_DOC)
    def forward(
        self,
        inputs=None,
        attention_mask=None,
        subsampled_output_points=None,
        head_mask=None,
        output_attentions=None,
        output_hidden_states=None,
        labels=None,
        return_dict=None,
    ):
        r"""
        labels (:obj:`torch.LongTensor` of shape :obj:`(batch_size,)`, `optional`):
            Labels for computing the image classification/regression loss. Indices should be in :obj:`[0, ...,
            config.num_labels - 1]`. If :obj:`config.num_labels == 1` a regression loss is computed (Mean-Square loss),
            If :obj:`config.num_labels > 1` a classification loss is computed (Cross-Entropy).

        Returns:

        Examples::

            >>> from transformers import PerceiverForMultimodalAutoencoding
            >>> import torch

            >>> images = torch.randn((1, 16, 3, 224, 224))
            >>> audio = torch.randn((1, 30720, 1))
            >>> inputs = dict(image=images, audio=audio, label=torch.zeros((images.shape[0], 700)))

            >>> model = PerceiverForMultimodalAutoencoding.from_pretrained('deepmind/multimodal-perceiver')

            >>> outputs = model(inputs=inputs)
            >>> logits = outputs.logits
        """
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        outputs = self.perceiver(
            inputs=inputs,
            attention_mask=attention_mask,
            subsampled_output_points=subsampled_output_points,
            head_mask=head_mask,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )
        logits = outputs.logits if return_dict else outputs[0]

        loss = None
        if labels is not None:
            raise NotImplementedError("Multimodal autoencoding training is not yet supported")

        if not return_dict:
            output = (logits,) + outputs[2:]
            return ((loss,) + output) if loss is not None else output

        return PerceiverClassifierOutput(
            loss=loss,
            logits=logits,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
            cross_attentions=outputs.cross_attentions,
        )


# Below: position encodings


def build_position_encoding(
    position_encoding_type,
    out_channels=None,
    project_pos_dim=-1,
    trainable_position_encoding_kwargs=None,
    fourier_position_encoding_kwargs=None,
):
    """
    Builds the position encoding.

    Args:

    - out_channels: refers to the number of channels of the position encodings.
    - project_pos_dim: if specified, will project the position encodings to this dimension.

    """

    if position_encoding_type == "trainable":
        if not trainable_position_encoding_kwargs:
            raise ValueError("Make sure to pass trainable_position_encoding_kwargs")
        output_pos_enc = PerceiverTrainablePositionEncoding(**trainable_position_encoding_kwargs)
    elif position_encoding_type == "fourier":
        # We don't use the index_dims argument, as this is only known during the forward pass
        if not fourier_position_encoding_kwargs:
            raise ValueError("Make sure to pass fourier_position_encoding_kwargs")
        output_pos_enc = PerceiverFourierPositionEncoding(**fourier_position_encoding_kwargs)
    else:
        raise ValueError(f"Unknown position encoding type: {position_encoding_type}.")

    # Optionally, project the position encoding to a target dimension:
    positions_projection = nn.Linear(out_channels, project_pos_dim) if project_pos_dim > 0 else nn.Identity()

    return output_pos_enc, positions_projection


# Below: Perceiver decoders


class PerceiverAbstractDecoder(nn.Module, metaclass=abc.ABCMeta):
    """Perceiver abstract decoder."""

    @abc.abstractmethod
    def decoder_query(self, inputs, modality_sizes=None, inputs_without_pos=None, subsampled_points=None):
        raise NotImplementedError

    @property
    @abc.abstractmethod
    def num_query_channels(self):
        raise NotImplementedError

    @abc.abstractmethod
    def forward(self, query, z, query_mask=None):
        raise NotImplementedError


class PerceiverProjectionDecoder(PerceiverAbstractDecoder):
    """
    Baseline projection decoder (no cross-attention).

    Args:
        config ([`PerceiverConfig`]):
            Model configuration.
    """

    def __init__(self, config):
        super().__init__()
        self.classifier = nn.Linear(config.d_latents, config.num_labels)

    def decoder_query(self, inputs, modality_sizes=None, inputs_without_pos=None, subsampled_points=None):
        return None

    def forward(self, query, z, query_mask=None):
        # (batch_size, num_latents, d_latents) -> (batch_size, d_latents)
        z = torch.mean(z, dim=1)
        # (batch_size, d_latents) -> (batch_size, config.num_labels)
        logits = self.classifier(z)
        return logits


class PerceiverBasicDecoder(PerceiverAbstractDecoder):
    """
    Cross-attention-based decoder. This class can be used to decode the final hidden states of the latents using a
    cross-attention operation, in which the latents produce keys and values.

    The shape of the output of this class depends on how one defines the output queries (also called decoder queries).

    Args:
        config ([`PerceiverConfig`]):
            Model configuration.
        output_num_channels (:obj:`int`, `optional`):
            The number of channels in the output. Will only be used in case `final_project` is set to `True`.
        position_encoding_type (:obj:`str`, `optional`, defaults to "trainable"):
            The type of position encoding to use. Can be either "trainable", "fourier", or "none".
        output_index_dims (:obj:`int`, `optional`):
            The number of dimensions of the output queries. Ignored if 'position_encoding_type' == 'none'.
        num_channels (:obj:`int`, `optional`):
            The number of channels of the decoder queries. Ignored if 'position_encoding_type' == 'none'.
        qk_channels (:obj:`int`, `optional`):
            The number of channels of the queries and keys in the cross-attention layer.
        v_channels (:obj:`int`, `optional`, defaults to 128):
            The number of channels of the values in the cross-attention layer.
        num_heads (:obj:`int`, `optional`, defaults to 1):
            The number of attention heads in the cross-attention layer.
        widening_factor (:obj:`int`, `optional`, defaults to 1):
            The widening factor of the cross-attention layer.
        use_query_residual (:obj:`bool`, `optional`, defaults to :obj:`False`):
            Whether to use a residual connection between the query and the output of the cross-attention layer.
        concat_preprocessed_input (:obj:`bool`, `optional`, defaults to :obj:`False`):
            Whether to concatenate the preprocessed input to the query.
        final_project (:obj:`bool`, `optional`, defaults to :obj:`True`):
            Whether to project the output of the cross-attention layer to a target dimension.
        position_encoding_only (:obj:`bool`, `optional`, defaults to :obj:`False`):
            Whether to only use this class to define output queries.
    """

    def __init__(
        self,
        config,
        output_num_channels,
        position_encoding_type="trainable",
        # The following 2 arguments are ignored if position_encoding_type == 'none':
        output_index_dims=None,
        num_channels=128,
        subsampled_index_dims=None,
        qk_channels=None,
        v_channels=None,
        num_heads=1,
        widening_factor=1,
        use_query_residual=False,
        concat_preprocessed_input=False,
        final_project=True,
        position_encoding_only=False,
        **position_encoding_kwargs,
    ):
        super().__init__()

        self.output_num_channels = output_num_channels
        # If `none`, the decoder will not construct any position encodings.
        # You should construct your own when quering the decoder.
        self.output_position_encodings = None
        self.position_encoding_type = position_encoding_type
        self.position_encoding_kwargs = position_encoding_kwargs
        if position_encoding_type != "none":
            self.output_position_encodings, self.positions_projection = build_position_encoding(
                position_encoding_type=position_encoding_type, **position_encoding_kwargs
            )

        self.output_index_dims = output_index_dims
        self.num_channels = num_channels
        if subsampled_index_dims is None:
            subsampled_index_dims = output_index_dims
        self.subsampled_index_dims = subsampled_index_dims
        self.concat_preprocessed_input = concat_preprocessed_input
        self.final_project = final_project
        self.position_encoding_only = position_encoding_only

        # for multimodal autoencoding, we don't need the decoder cross-attention and final layer
        # so then we will set position_encoding_only to True
        if not self.position_encoding_only:
            self.decoding_cross_attention = PerceiverLayer(
                config,
                is_cross_attention=True,
                qk_channels=qk_channels,
                v_channels=v_channels,
                num_heads=num_heads,
                q_dim=num_channels,
                kv_dim=config.d_latents,
                widening_factor=widening_factor,
                use_query_residual=use_query_residual,
            )
            self.final_layer = nn.Linear(num_channels, output_num_channels) if final_project else nn.Identity()

    @property
    def num_query_channels(self) -> int:
        if self.position_encoding_type == "none":  # Queries come from elsewhere
            raise ValueError(
                "You cannot calculate number of decoder query channels when position_encoding_type is set to none"
            )
        if self.position_encoding_only:
            if "project_pos_dim" in self.position_encoding_kwargs:
                return self.position_encoding_kwargs["project_pos_dim"]
            return self.output_position_encodings.output_size()
        if self.final_project:
            return self.output_num_channels
        return self.num_channels

    def decoder_query(self, inputs, modality_sizes=None, inputs_without_pos=None, subsampled_points=None):
        if self.position_encoding_type == "none":  # Queries come from elsewhere
            raise ValueError("You cannot construct decoder queries when position_encoding_type is set to none")
        if subsampled_points is not None:
            # subsampled_points are the indices if the inputs would be flattened
            # however, the inputs aren't flattened, that's why we use unravel_index
            # to get the indices for the unflattened array
            # unravel_index returns a tuple (x_idx, y_idx, ...)
            # stack to get the [n, d] tensor of coordinates
            indices = list(torch.from_numpy(x) for x in np.unravel_index(subsampled_points, self.output_index_dims))
            pos = torch.stack(indices, dim=1)
            batch_size = inputs.shape[0]
            # Map these coordinates to [-1, 1]
            pos = -1 + 2 * pos / torch.tensor(self.output_index_dims)[None, :]
            pos = torch.broadcast_to(pos[None], [batch_size, pos.shape[0], pos.shape[1]])
            # Construct the position encoding.
            if self.position_encoding_type == "trainable":
                pos_emb = self.output_position_encodings(batch_size)
            elif self.position_encoding_type == "fourier":
                pos_emb = self.output_position_encodings(
                    self.output_index_dims, batch_size=batch_size, device=inputs.device, pos=pos
                )

            # Optionally project them to a target dimension.
            pos_emb = self.positions_projection(pos_emb)
            pos_emb = torch.reshape(pos_emb, [pos_emb.shape[0], -1, pos_emb.shape[-1]])
        else:
            batch_size = inputs.shape[0]
            index_dims = inputs.shape[2:]

            # Construct the position encoding.
            if self.position_encoding_type == "trainable":
                pos_emb = self.output_position_encodings(batch_size)
            elif self.position_encoding_type == "fourier":
                pos_emb = self.output_position_encodings(index_dims, batch_size, device=inputs.device)

            # Optionally project them to a target dimension.
            pos_emb = self.positions_projection(pos_emb)

        if self.concat_preprocessed_input:
            if inputs_without_pos is None:
                raise ValueError("Value is required for inputs_without_pos if concat_preprocessed_input is True")
            pos_emb = torch.cat([inputs_without_pos, pos_emb], div=-1)

        return pos_emb

    def forward(self, query, z, query_mask=None, output_attentions=False):
        # Cross-attention decoding.
        # key, value: B x N x K; query: B x M x K
        # Attention maps -> B x N x M
        # Output -> B x M x K
        cross_attentions = () if output_attentions else None

        layer_outputs = self.decoding_cross_attention(
            query,
            attention_mask=query_mask,
            head_mask=None,
            inputs=z,
            inputs_mask=None,
            output_attentions=output_attentions,
        )
        output = layer_outputs[0]

        if output_attentions:
            cross_attentions = cross_attentions + (layer_outputs[1],)

        logits = self.final_layer(output)

        return PerceiverDecoderOutput(logits=logits, cross_attentions=cross_attentions)


class PerceiverClassificationDecoder(PerceiverAbstractDecoder):
    """
    Cross-attention based classification decoder. Light-weight wrapper of [`PerceiverBasicDecoder`] for logit output.
    Will turn the output of the Perceiver encoder which is of shape (batch_size, num_latents, d_latents) to a tensor of
    shape (batch_size, num_labels). The queries are of shape (batch_size, 1, num_labels).

    Args:
        config ([`PerceiverConfig`]):
            Model configuration.
    """

    def __init__(self, config, **decoder_kwargs):
        super().__init__()

        self.num_labels = config.num_labels
        self.decoder = PerceiverBasicDecoder(
            config,
            output_num_channels=self.num_labels,
            output_index_dims=1,  # Predict a single logit array.
            **decoder_kwargs,
        )

    @property
    def num_query_channels(self) -> int:
        return self.decoder.num_query_channels

    def decoder_query(self, inputs, modality_sizes=None, inputs_without_pos=None, subsampled_points=None):
        return self.decoder.decoder_query(
            inputs, modality_sizes, inputs_without_pos, subsampled_points=subsampled_points
        )

    def forward(self, query, z, query_mask=None, output_attentions=False):
        decoder_outputs = self.decoder(query, z, output_attentions=output_attentions)

        # B x 1 x num_classes -> B x num_classes
        logits = decoder_outputs.logits[:, 0, :]

        return PerceiverDecoderOutput(logits=logits, cross_attentions=decoder_outputs.cross_attentions)


class PerceiverOpticalFlowDecoder(PerceiverAbstractDecoder):
    """Cross-attention based optical flow decoder."""

    def __init__(self, config, output_image_shape, output_num_channels=2, rescale_factor=100.0, **decoder_kwargs):
        super().__init__()

        self.output_image_shape = output_image_shape
        self.output_num_channels = output_num_channels
        self.rescale_factor = rescale_factor
        self.decoder = PerceiverBasicDecoder(config, output_num_channels=output_num_channels, **decoder_kwargs)

    @property
    def num_query_channels(self) -> int:
        return self.decoder.num_query_channels

    def decoder_query(self, inputs, modality_sizes=None, inputs_without_pos=None, subsampled_points=None):
        if subsampled_points is not None:
            raise ValueError("FlowDecoder doesn't support subsampling yet.")
        return inputs

    def forward(self, query, z, query_mask=None, output_attentions=False):
        decoder_outputs = self.decoder(query, z, output_attentions=output_attentions)
        preds = decoder_outputs.logits
        # Output flow and rescale.
        preds /= self.rescale_factor
        preds = preds.reshape([preds.shape[0]] + list(self.output_image_shape) + [preds.shape[-1]])
        return PerceiverDecoderOutput(logits=preds, cross_attentions=decoder_outputs.cross_attentions)


class PerceiverBasicVideoAutoencodingDecoder(PerceiverAbstractDecoder):
    """
    Cross-attention based video-autoencoding decoder. Light-weight wrapper of [`PerceiverBasicDecoder`] with video
    reshaping logic.

    Args:
        config ([`PerceiverConfig`]):
            Model configuration.
        output_shape (:obj:`List[int]`):
            Shape of the output as (batch_size, num_frames, height, width), excluding the channel dimension.
        position_encoding_type (:obj:`str`):
            The type of position encoding to use. Can be either "trainable", "fourier", or "none".
    """

    def __init__(self, config, output_shape, position_encoding_type, **decoder_kwargs):
        super().__init__()
        if len(output_shape) != 4:  # B, T, H, W
            raise ValueError(f"Expected rank 4 output_shape, got {output_shape}.")
        # Build the decoder components:
        self.output_shape = output_shape
        self.output_num_channels = decoder_kwargs["output_num_channels"]

        self.decoder = PerceiverBasicDecoder(
            config,
            output_index_dims=self.output_shape[1:4],  # T*H*W
            position_encoding_type=position_encoding_type,
            **decoder_kwargs,
        )

    @property
    def num_query_channels(self) -> int:
        return self.decoder.num_query_channels

    def decoder_query(self, inputs, modality_sizes=None, inputs_without_pos=None, subsampled_points=None):
        return self.decoder.decoder_query(
            inputs,
            modality_sizes=modality_sizes,
            inputs_without_pos=inputs_without_pos,
            subsampled_points=subsampled_points,
        )

    def forward(self, query, z, query_mask=None):
        decoder_outputs = self.decoder(query, z)
        logits = decoder_outputs.logits

        logits = torch.reshape(logits, self.output_shape + [logits.shape[-1]])
        return PerceiverDecoderOutput(logits=logits, cross_attentions=decoder_outputs.cross_attentions)


def restructure(modality_sizes: ModalitySizeType, inputs: torch.Tensor) -> Mapping[str, torch.Tensor]:
    """
    Partitions a [B, N, C] tensor into tensors for each modality.

    Args:
        modality_sizes
            dict specifying the size of the modality
        inputs:
            input tensor

    Returns:
        dict mapping name of modality to its associated tensor.
    """
    outputs = {}
    index = 0
    # Apply a predictable ordering to the modalities
    for modality in sorted(modality_sizes.keys()):
        size = modality_sizes[modality]
        inp = inputs[:, index : index + size]
        index += size
        outputs[modality] = inp
    return outputs


class PerceiverMultimodalDecoder(PerceiverAbstractDecoder):
    """
    Multimodal decoding by composing uni-modal decoders. The `modalities` argument of the constructor is a dictionary
    mapping modality name to the decoder of that modality. That decoder will be used to construct queries for that
    modality. Modality-specific queries are padded with trainable modality-specific parameters, after which they are
    concatenated along the time dimension.

    Next, there is a shared cross attention operation across all modalities.

    Args:
        config ([`PerceiverConfig`]):
            Model configuration.
        modalities (:obj:`Dict[str, PerceiverAbstractDecoder]`):
            Dictionary mapping modality name to the decoder of that modality.
        num_outputs (:obj:`int`):
            The number of outputs of the decoder.
        output_num_channels (:obj:`int`):
            The number of channels in the output.
        min_padding_size (:obj:`int`, `optional`, defaults to 2):
            The minimum padding size for all modalities. The final output will have num_channels equal to the maximum
            channels across all modalities plus min_padding_size.
        subsampled_index_dims (:obj:`Dict[str, PerceiverAbstractDecoder]`, `optional`):
            Dictionary mapping modality name to the subsampled index dimensions to use for the decoder query of that
            modality.
    """

    def __init__(
        self,
        config,
        modalities,
        num_outputs,
        output_num_channels,
        min_padding_size=2,
        subsampled_index_dims=None,
        **decoder_kwargs
    ):
        super().__init__()
        self.modalities = nn.ModuleDict(modalities)
        self.subsampled_index_dims = subsampled_index_dims
        self.min_padding_size = min_padding_size
        self.output_num_channels = output_num_channels
        self.num_outputs = num_outputs
        self.decoder = PerceiverBasicDecoder(
            config,
            output_index_dims=(num_outputs,),
            output_num_channels=output_num_channels,
            position_encoding_type="none",
            num_channels=self.num_query_channels,
            **decoder_kwargs,
        )
        self.padding = nn.ParameterDict(
            {
                modality: nn.Parameter(torch.randn(1, self.num_query_channels - decoder.num_query_channels))
                for modality, decoder in modalities.items()
            }
        )

    @property
    def num_query_channels(self) -> int:
        max_channel_size = max(decoder.num_query_channels for _, decoder in self.modalities.items())
        common_channel_size = max_channel_size + self.min_padding_size
        return common_channel_size

    def decoder_query(self, inputs, modality_sizes, inputs_without_pos=None, subsampled_points=None):
        # Partition the flat inputs among the different modalities
        inputs = restructure(modality_sizes, inputs)

        # Obtain modality-specific decoders' queries
        subsampled_points = subsampled_points or dict()

        decoder_queries = dict()
        for modality, decoder in self.modalities.items():
            # Get input_without_pos for this modality if it exists.
            input_without_pos = None
            if inputs_without_pos is not None:
                input_without_pos = inputs_without_pos.get(modality, None)
            query = decoder.decoder_query(
                inputs=inputs[modality],
                modality_sizes=None,
                inputs_without_pos=input_without_pos,
                subsampled_points=subsampled_points.get(modality, None),
            )
            decoder_queries[modality] = query

        # Pad all queries with trainable position encodings to make them have the same channels

        def embed(modality, x):
            x = torch.reshape(x, [x.shape[0], np.prod(x.shape[1:-1]), x.shape[-1]])
            pos = self.padding[modality]
            pos = torch.broadcast_to(pos, [x.shape[0], x.shape[1], self.num_query_channels - x.shape[2]])
            return torch.cat([x, pos], dim=2)

        # Apply a predictable ordering to the modalities
        return torch.cat(
            [embed(modality, decoder_queries[modality]) for modality in sorted(self.modalities.keys())], dim=1
        )

    def forward(self, query, z, query_mask=None, output_attentions=False):
        # B x 1 x num_classes -> B x num_classes
        decoder_outputs = self.decoder(query, z, output_attentions=output_attentions)

        return decoder_outputs


# Below: IO pre- and post-processor classes for Perceiver.
def space_to_depth(frames: torch.Tensor, temporal_block_size: int = 1, spatial_block_size: int = 1) -> torch.Tensor:
    """
    Space to depth transform. Rearranges blocks of spatial data, into depth.

    This function assumes the channels to be first, but will place the channels last after transformation.

    Based on https://discuss.pytorch.org/t/is-there-any-layer-like-tensorflows-space-to-depth-function/3487/15.
    """
    if len(frames.shape) == 4:
        batch_size, num_channels, height, width = frames.shape
        # split up dimensions (height by spatial_block_size, width by spatial_block_size)
        frames = frames.view(
            batch_size,
            num_channels,
            height // spatial_block_size,
            spatial_block_size,
            width // spatial_block_size,
            spatial_block_size,
        )
        # move blocks to last dimension: (batch_size, H//bs, W//bs, bs, bs, C)
        frames = frames.permute(0, 2, 4, 3, 5, 1).contiguous()
        # concatenate blocks along channel dimension: (batch_size, H//bs, W//bs, bs*bs*C)
        frames = frames.view(
            batch_size,
            height // spatial_block_size,
            width // spatial_block_size,
            (spatial_block_size ** 2) * num_channels,
        )
        return frames
    elif len(frames.shape) == 5:
        batch_size, time, num_channels, height, width = frames.shape
        # split up dimensions (time by temporal_block_size, height by spatial_block_size, width by spatial_block_size)
        frames = frames.view(
            batch_size,
            time // temporal_block_size,
            temporal_block_size,
            num_channels,
            height // spatial_block_size,
            spatial_block_size,
            width // spatial_block_size,
            spatial_block_size,
        )
        # move blocks to last dimension: (batch_size, T//ts, H//bs, W//bs, ts, bs, bs, C)
        frames = frames.permute(0, 1, 4, 6, 2, 5, 7, 3).contiguous()
        # concatenate blocks along channel dimension: (batch_size, T//ts, H//bs, W//bs, ts*bs*bs*C)
        frames = frames.view(
            batch_size,
            time // temporal_block_size,
            height // spatial_block_size,
            width // spatial_block_size,
            temporal_block_size * (spatial_block_size ** 2) * num_channels,
        )
        return frames
    else:
        raise ValueError(
            "Frames should be of rank 4 (batch, channels, height, width)"
            " or rank 5 (batch, time, channels, height, width)"
        )


class Conv2dSamePadding(nn.Conv2d):
    """
    Conv2d layer with padding="same" support. Source:
    https://gist.github.com/sumanmichael/4de9dee93f972d47c80c4ade8e149ea6
    """

    def __init__(self, *args, **kwargs):
        super(Conv2dSamePadding, self).__init__(*args, **kwargs)
        self.zero_pad_2d = nn.ZeroPad2d(
            reduce(__add__, [(k // 2 + (k - 2 * (k // 2)) - 1, k // 2) for k in self.kernel_size[::-1]])
        )

    def forward(self, input):
        return self._conv_forward(self.zero_pad_2d(input), self.weight, self.bias)


class Conv2DDownsample(nn.Module):
    """Downsamples 4x by applying a 2D convolution and doing max pooling."""

    def __init__(
        self,
        num_layers: int = 1,
        in_channels: int = 3,
        out_channels: int = 64,
        use_batchnorm: bool = True,
    ):
        """
        Constructs a Conv2DDownsample model.

        Args:
          in_channels (:obj:`int`, `optional`, defaults to 3):
            The number of input channels.
          out_channels (:obj:`int`, `optional`, defaults to 64):
            The number of conv output channels.
          use_batchnorm (:obj:`bool`, `optional`, defaults to :obj:`True`):
            Whether to use batchnorm.
        """
        super().__init__()

        self.conv = Conv2dSamePadding(
            in_channels=in_channels, out_channels=out_channels, kernel_size=7, stride=2, bias=False
        )
        self.batchnorm = nn.BatchNorm2d(num_features=out_channels) if use_batchnorm else nn.Identity()
        self.relu = nn.ReLU()
        self.max_pool = nn.MaxPool2d(kernel_size=3, stride=2)

    def forward(self, inputs: torch.Tensor) -> torch.Tensor:
        out = self.conv(inputs)
        out = self.batchnorm(out)
        out = self.relu(out)
        out = self.max_pool(out)
        return out


def generate_fourier_features(pos, num_bands, max_resolution=(224, 224), concat_pos=True, sine_only=False):
    """
    Generate a Fourier frequency position encoding with linear spacing.

    Args:
      pos (:obj:`torch.LongTensor` of shape :obj:`(batch_size, sequence_length, dim)`):
        The Tensor containing the position of n points in d dimensional space.
      num_bands (:obj:`int`):
        The number of frequency bands (K) to use.
      max_resolution (:obj:`Tuple[int]`, `optional`, defaults to (224, 224)):
        The maximum resolution (i.e. the number of pixels per dim). A tuple representing resolution for each dimension.
      concat_pos (:obj:`bool`, `optional`, defaults to :obj:`True`):
        Whether to concatenate the input position encoding to the Fourier features.
      sine_only (:obj:`bool`, `optional`, defaults to :obj:`False`):
        Whether to use a single phase (sin) or two (sin/cos) for each frequency band.

    Returns:
      :obj:`torch.FloatTensor` of shape :obj:`(batch_size, sequence_length, n_channels)`: The Fourier position
      embeddings. If :obj:`concat_pos` is `True` and :obj:`sine_only` is `False`, output dimensions are ordered as:
      [dim_1, dim_2, ..., dim_d, sin(pi*f_1*dim_1), ..., sin(pi*f_K*dim_1), ..., sin(pi*f_1*dim_d), ...,
      sin(pi*f_K*dim_d), cos(pi*f_1*dim_1), ..., cos(pi*f_K*dim_1), ..., cos(pi*f_1*dim_d), ..., cos(pi*f_K*dim_d)],
      where dim_i is pos[:, i] and f_k is the kth frequency band.
    """

    batch_size = pos.shape[0]

    min_freq = 1.0
    # Nyquist frequency at the target resolution:
    freq_bands = torch.stack(
        [torch.linspace(start=min_freq, end=res / 2, steps=num_bands) for res in max_resolution], dim=0
    )

    # Get frequency bands for each spatial dimension.
    # Output is size [n, d * num_bands]
    per_pos_features = pos[0, :, :][:, :, None] * freq_bands[None, :, :]
    per_pos_features = torch.reshape(per_pos_features, [-1, np.prod(per_pos_features.shape[1:])])

    if sine_only:
        # Output is size [n, d * num_bands]
        per_pos_features = torch.sin(np.pi * (per_pos_features))
    else:
        # Output is size [n, 2 * d * num_bands]
        per_pos_features = torch.cat(
            [torch.sin(np.pi * per_pos_features), torch.cos(np.pi * per_pos_features)], dim=-1
        )
    # Concatenate the raw input positions.
    if concat_pos:
        # Adds d bands to the encoding.
        per_pos_features = torch.cat([pos, per_pos_features.expand(batch_size, -1, -1)], dim=-1)
    return per_pos_features


def build_linear_positions(index_dims, output_range=(-1.0, 1.0)):
    """
    Generate an array of position indices for an N-D input array.

    Args:
      index_dims (:obj:`List[int]`):
        The shape of the index dimensions of the input array.
      output_range (:obj:`Tuple[float]`, `optional`, defaults to :obj:`(-1.0, 1.0)`):
        The min and max values taken by each input index dimension.

    Returns:
      :obj:`torch.FloatTensor` of shape :obj:`(index_dims[0], index_dims[1], .., index_dims[-1], N)`.
    """

    def _linspace(n_xels_per_dim):
        return torch.linspace(start=output_range[0], end=output_range[1], steps=n_xels_per_dim, dtype=torch.float32)

    dim_ranges = [_linspace(n_xels_per_dim) for n_xels_per_dim in index_dims]
    array_index_grid = torch.meshgrid(*dim_ranges)

    return torch.stack(array_index_grid, dim=-1)


class PerceiverAbstractPositionEncoding(nn.Module, metaclass=abc.ABCMeta):
    """Perceiver abstract position encoding."""

    @property
    @abc.abstractmethod
    def num_dimensions(self) -> int:
        raise NotImplementedError

    @abc.abstractmethod
    def output_size(self, *args, **kwargs) -> int:
        raise NotImplementedError

    @abc.abstractmethod
    def forward(self, batch_size, pos):
        raise NotImplementedError


class PerceiverTrainablePositionEncoding(PerceiverAbstractPositionEncoding):
    """Trainable position encoding."""

    def __init__(self, index_dims, num_channels=128):
        super().__init__()
        self._num_channels = num_channels
        self._index_dims = index_dims
        index_dim = np.prod(index_dims)
        self.position_embeddings = nn.Parameter(torch.randn(index_dim, num_channels))

    @property
    def num_dimensions(self) -> int:
        if isinstance(self._index_dims, int):
            return 1
        return len(self._index_dims)

    def output_size(self, *args, **kwargs) -> int:
        return self._num_channels

    def forward(self, batch_size):
        position_embeddings = self.position_embeddings

        if batch_size is not None:
            position_embeddings = position_embeddings.expand(batch_size, -1, -1)
        return position_embeddings


def _check_or_build_spatial_positions(pos, index_dims, batch_size):
    """
    Checks or builds spatial position features (x, y, ...).

    Args:
      pos (:obj:`torch.FloatTensor`):
        None, or an array of position features. If None, position features are built. Otherwise, their size is checked.
      index_dims (:obj:`List[int]`):
        An iterable giving the spatial/index size of the data to be featurized.
      batch_size (:obj:`int`):
        The batch size of the data to be featurized.

    Returns:
        :obj:`torch.FloatTensor` of shape :obj:`(batch_size, prod(index_dims))` an array of position features.
    """
    if pos is None:
        pos = build_linear_positions(index_dims)
        pos = torch.broadcast_to(pos[None], (batch_size,) + pos.shape)
        pos = torch.reshape(pos, [batch_size, np.prod(index_dims), -1])
    else:
        # Just a warning label: you probably don't want your spatial features to
        # have a different spatial layout than your pos coordinate system.
        # But feel free to override if you think it'll work!
        if pos.shape[-1] != len(index_dims):
            raise ValueError("Spatial features have the wrong number of dimensions.")
    return pos


class PerceiverFourierPositionEncoding(PerceiverAbstractPositionEncoding):
    """Fourier (Sinusoidal) position encoding."""

    def __init__(self, num_bands, max_resolution, concat_pos=True, sine_only=False):
        super().__init__()
        self.num_bands = num_bands
        self.max_resolution = max_resolution
        self.concat_pos = concat_pos
        self.sine_only = sine_only

    @property
    def num_dimensions(self) -> int:
        return len(self.max_resolution)

    def output_size(self):
        """Returns size of positional encodings last dimension."""
        num_dims = len(self.max_resolution)
        encoding_size = self.num_bands * num_dims
        if not self.sine_only:
            encoding_size *= 2
        if self.concat_pos:
            encoding_size += self.num_dimensions

        return encoding_size

    def forward(self, index_dims, batch_size, device, pos=None):
        pos = _check_or_build_spatial_positions(pos, index_dims, batch_size)
        fourier_pos_enc = generate_fourier_features(
            pos,
            num_bands=self.num_bands,
            max_resolution=self.max_resolution,
            concat_pos=self.concat_pos,
            sine_only=self.sine_only,
        ).to(device)
        return fourier_pos_enc


class AbstractPreprocessor(nn.Module):
    @property
    def num_channels(self) -> int:
        """Returns size of preprocessor output."""
        raise NotImplementedError()


class PerceiverTextPreprocessor(AbstractPreprocessor):
    """
    Text preprocessing for Perceiver Encoder. Can be used to embed `inputs` and add positional encodings.

    The dimensionality of the embeddings is determined by the `d_model` attribute of the configuration.

    Args:
        config ([`PerceiverConfig`]):
            Model configuration.
    """

    def __init__(self, config):
        super().__init__()
        self.config = config
        self.embeddings = nn.Embedding(num_embeddings=config.vocab_size, embedding_dim=config.d_model)
        self.position_embeddings = nn.Embedding(config.max_position_embeddings, config.d_model)

    @property
    def num_channels(self) -> int:
        return self.config.d_model

    def forward(self, inputs):
        embeddings = self.embeddings(inputs)

        seq_length = inputs.shape[1]
        position_ids = torch.arange(0, seq_length, device=inputs.device)
        embeddings = embeddings + self.position_embeddings(position_ids)

        return embeddings, None, None


class PerceiverEmbeddingDecoder(nn.Module):
    """
    Module to decode embeddings (for masked language modeling).

    Args:
        config ([`PerceiverConfig`]):
            Model configuration.
    """

    def __init__(self, config):
        super().__init__()
        self.config = config
        self.vocab_size = config.vocab_size
        self.bias = nn.Parameter(torch.zeros(self.vocab_size))

    def forward(self, hidden_states, embedding_layer):
        batch_size, seq_len, d_model = hidden_states.shape
        output = torch.matmul(hidden_states.reshape([-1, d_model]), embedding_layer.weight.T)  # Flatten batch dim
        output = output + self.bias

        return output.reshape([batch_size, seq_len, self.vocab_size])


class PerceiverMultimodalPostprocessor(nn.Module):
    """
    Multimodal postprocessing for Perceiver. Can be used to combine modality-specific postprocessors into a single
    postprocessor.

    Args:
          modalities (:obj:`Dict[str, PostprocessorType]`):
            Dictionary mapping modality name to postprocessor class for that modality.
          input_is_dict (:obj:`bool`, `optional`, defaults to :obj:`False`):
            If True, input is assumed to be dictionary structured, and outputs keep the same dictionary shape. If
            False, input is a tensor which is sliced up during postprocessing by `modality_sizes`.
    """

    def __init__(self, modalities: Mapping[str, PostprocessorType], input_is_dict: bool = False):
        super().__init__()
        self.modalities = nn.ModuleDict(modalities)
        self.input_is_dict = input_is_dict

    def forward(
        self, inputs: torch.Tensor, pos: Optional[torch.Tensor] = None, modality_sizes=None
    ) -> Mapping[str, torch.Tensor]:
        if not self.input_is_dict:
            # Slice up modalities by their sizes.
            if modality_sizes is None:
                raise ValueError("Modality sizes should be specified if input is not a dictionary.")
            inputs = restructure(modality_sizes=modality_sizes, inputs=inputs)

        outputs = {
            modality: postprocessor(inputs[modality], pos=pos, modality_sizes=None)
            for modality, postprocessor in self.modalities.items()
        }
        return outputs


class PerceiverClassificationPostprocessor(nn.Module):
    """
    Classification postprocessing for Perceiver. Can be used to convert the decoder output to classification logits.

    Args:
        config ([`PerceiverConfig`]):
            Model configuration.
        in_channels (:obj:`int`):
            Number of channels in the input.
    """

    def __init__(self, config, in_channels):
        super().__init__()
        self.classifier = nn.Linear(in_channels, config.num_labels)

    def forward(self, inputs, pos: Optional[torch.Tensor] = None, modality_sizes=None) -> torch.Tensor:
        logits = self.classifier(inputs)
        return logits[:, 0, :]


class PerceiverAudioPostprocessor(nn.Module):
    """
    Audio postprocessing for Perceiver. Can be used to convert the decoder output to audio features.

    Args:
        config ([`PerceiverConfig`]):
            Model configuration.
        in_channels (:obj:`int`):
            Number of channels in the input.
        postproc_type (:obj:`str`, `optional`, defaults to :obj:`"patches"`):
            Postprocessor type to use. Currently, only "patches" is supported.
    """

    def __init__(self, config, in_channels, postproc_type: str = "patches"):
        super().__init__()

        if postproc_type not in ("patches",):  # to be supported: 'conv', 'patches', 'pixels'
            raise ValueError("Invalid postproc_type!")

        # Architecture parameters:
        self.classifier = nn.Linear(in_channels, config.samples_per_patch)

    def forward(self, inputs: torch.Tensor, pos: Optional[torch.Tensor] = None, modality_sizes=None) -> torch.Tensor:

        logits = self.classifier(inputs)
        return torch.reshape(logits, [inputs.shape[0], -1])


class PerceiverProjectionPostprocessor(nn.Module):
    """
    Projection postprocessing for Perceiver. Can be used to project the channels of the decoder output to a lower
    dimension.

    Args:
        in_channels (:obj:`int`):
            Number of channels in the input.
        out_channels (:obj:`int`):
            Number of channels in the output.
    """

    def __init__(self, in_channels, out_channels):
        super().__init__()
        self.classifier = nn.Linear(in_channels, out_channels)

    def forward(self, inputs: torch.Tensor, pos: Optional[torch.Tensor] = None, modality_sizes=None) -> torch.Tensor:
        logits = self.classifier(inputs)
        return logits


class PerceiverImagePreprocessor(AbstractPreprocessor):
    """
    Image preprocessing for Perceiver Encoder.

    Note: the `out_channels` argument refers to the output channels of a convolutional layer, if `prep_type` is set to
    "conv1x1" or "conv". If one adds absolute position embeddings, one must make sure the `num_channels` of the
    position encoding kwargs are set equal to the `out_channels`.

    Args:
        config ([`PerceiverConfig`]):
            Model configuration.
        prep_type (:obj:`str`, `optional`, defaults to :obj:`"conv"`):
            Preprocessing type. Can be "conv1x1", "conv", "patches", "pixels".
        spatial_downsample (:obj:`int`, `optional`, defaults to 4):
            Spatial downsampling factor.
        temporal_downsample (:obj:`int`, `optional`, defaults to 1):
            Temporal downsampling factor (only relevant in case a time dimension is present).
        position_encoding_type (:obj:`str`, `optional`, defaults to :obj:`"fourier"`):
            Position encoding type. Can be "fourier" or "trainable".
        in_channels (:obj:`int`, `optional`, defaults to 3):
            Number of channels in the input.
        out_channels (:obj:`int`, `optional`, defaults to 64):
            Number of channels in the output.
        conv_after_patching (:obj:`bool`, `optional`, defaults to :obj:`False`):
            Whether to apply a convolutional layer after patching.
        conv_after_patching_in_channels (:obj:`int`, `optional`, defaults to 54):
            Number of channels in the input of the convolutional layer after patching.
        conv2d_use_batchnorm (:obj:`bool`, `optional`, defaults to :obj:`True`):
            Whether to use batch normalization in the convolutional layer.
        concat_or_add_pos (:obj:`str`, `optional`, defaults to :obj:`"concat"`):
            How to concatenate the position encoding to the input. Can be "concat" or "add".
        project_pos_dim (:obj:`int`, `optional`, defaults to -1):
            Dimension of the position encoding to project to. If -1, no projection is applied.
        **position_encoding_kwargs (:obj:`Dict`, `optional`):
            Keyword arguments for the position encoding.
    """

    def __init__(
        self,
        config,
        prep_type="conv",
        spatial_downsample: int = 4,
        temporal_downsample: int = 1,
        position_encoding_type: str = "fourier",
        in_channels: int = 3,
        out_channels: int = 64,
        conv_after_patching: bool = False,
        conv_after_patching_in_channels: int = 54,  # only relevant when conv_after_patching = True
        conv2d_use_batchnorm: bool = True,
        concat_or_add_pos: str = "concat",
        project_pos_dim: int = -1,
        **position_encoding_kwargs,
    ):
        super().__init__()
        self.config = config

        if prep_type not in ("conv", "patches", "pixels", "conv1x1"):
            raise ValueError(f"Prep_type {prep_type} is invalid")

        if concat_or_add_pos not in ["concat", "add"]:
            raise ValueError(f"Invalid value {concat_or_add_pos} for concat_or_add_pos.")

        self.in_channels = in_channels
        self.prep_type = prep_type
        self.spatial_downsample = spatial_downsample
        self.temporal_downsample = temporal_downsample
        self.position_encoding_type = position_encoding_type
        self.concat_or_add_pos = concat_or_add_pos
        self.conv_after_patching = conv_after_patching
        self.out_channels = out_channels

        if self.prep_type == "conv":
            # Downsampling with conv is currently restricted
            convnet_num_layers = math.log(spatial_downsample, 4)
            convnet_num_layers_is_int = convnet_num_layers == np.round(convnet_num_layers)
            if not convnet_num_layers_is_int or temporal_downsample != 1:
                raise ValueError(
                    "Only powers of 4 expected for spatial and 1 expected for temporal downsampling with conv."
                )
            self.convnet = Conv2DDownsample(
                in_channels=in_channels,
                num_layers=int(convnet_num_layers),
                out_channels=out_channels,
                use_batchnorm=conv2d_use_batchnorm,
            )

        elif self.prep_type == "conv1x1":
            if temporal_downsample != 1:
                raise ValueError("Conv1x1 does not downsample in time.")
            self.convnet_1x1 = nn.Conv2d(
                in_channels=in_channels,
                out_channels=out_channels,
                kernel_size=(1, 1),
                # spatial_downsample is unconstrained for 1x1 convolutions.
                stride=(spatial_downsample, spatial_downsample),
            )

        # Position embeddings
        self.project_pos_dim = project_pos_dim
        self.position_embeddings, self.positions_projection = build_position_encoding(
            position_encoding_type=position_encoding_type,
            out_channels=out_channels,
            project_pos_dim=project_pos_dim,
            **position_encoding_kwargs,
        )

        # Optional convolutional layer after patches.
        self.conv_after_patches = (
            nn.Linear(conv_after_patching_in_channels, self.out_channels) if conv_after_patching else nn.Identity()
        )

    @property
    def num_channels(self) -> int:
        # Let's assume that the number of resolutions (in the context of image preprocessing)
        # of the input data is 2 or 3 depending on whether we are processing image or video respectively.
        # In this case, for convenience, we will declare is_temporal variable,
        # which will show whether the data has a temporal dimension or not.
        is_temporal = self.position_embeddings.num_dimensions > 2

        # position embedding
        if self.project_pos_dim > 0:
            pos_dim = self.project_pos_dim
        else:
            pos_dim = self.position_embeddings.output_size()
        if self.concat_or_add_pos == "add":
            return pos_dim

        # inputs
        if self.conv_after_patching or self.prep_type in ("conv1x1", "conv"):
            inp_dim = self.out_channels
        elif self.prep_type == "pixels":
            inp_dim = self.in_channels
            if not is_temporal:
                inp_dim = math.ceil(inp_dim / self.spatial_downsample)
        elif self.prep_type == "patches":
            if self.conv_after_patching:
                inp_dim = self.out_channels
            else:
                inp_dim = self.in_channels * self.spatial_downsample ** 2
                if is_temporal:
                    inp_dim *= self.temporal_downsample

        return inp_dim + pos_dim

    def _build_network_inputs(self, inputs: torch.Tensor, pos: torch.Tensor, network_input_is_1d: bool = True):
        """
        Construct the final input, including position encoding.

        This method expects the inputs to always have channels as last dimension.

        """
        batch_size = inputs.shape[0]
        index_dims = inputs.shape[1:-1]
        indices = np.prod(index_dims)

        # Flatten input features to a 1D index dimension if necessary.
        if len(inputs.shape) > 3 and network_input_is_1d:
            inputs = torch.reshape(inputs, [batch_size, indices, -1])

        # Construct the position encoding.
        if self.position_encoding_type == "trainable":
            pos_enc = self.position_embeddings(batch_size)
        elif self.position_encoding_type == "fourier":
            pos_enc = self.position_embeddings(index_dims, batch_size, device=inputs.device)

        # Optionally project them to a target dimension.
        pos_enc = self.positions_projection(pos_enc)

        if not network_input_is_1d:
            # Reshape pos to match the input feature shape
            # if the network takes non-1D inputs
            sh = inputs.shape
            pos_enc = torch.reshape(pos_enc, list(sh)[:-1] + [-1])
        if self.concat_or_add_pos == "concat":
            inputs_with_pos = torch.cat([inputs, pos_enc], dim=-1)
        elif self.concat_or_add_pos == "add":
            inputs_with_pos = inputs + pos_enc
        return inputs_with_pos, inputs

    def forward(self, inputs: torch.Tensor, pos: Optional[torch.Tensor] = None, network_input_is_1d: bool = True):
        if self.prep_type == "conv":
            # Convnet image featurization.
            # Downsamples spatially by a factor of 4
            inputs = self.convnet(inputs)

        elif self.prep_type == "conv1x1":
            # map inputs to self.out_channels
            inputs = self.convnet_1x1(inputs)

        elif self.prep_type == "pixels":
            # if requested, downsamples in the crudest way
            if inputs.ndim == 4:
                inputs = inputs[:: self.spatial_downsample, :: self.spatial_downsample]
            elif inputs.ndim == 5:
                inputs = inputs[
                    :, :: self.temporal_downsample, :, :: self.spatial_downsample, :: self.spatial_downsample
                ]
            else:
                raise ValueError("Unsupported data format for pixels.")

        elif self.prep_type == "patches":
            # Space2depth featurization.
            # Video: B x T x C x H x W
            inputs = space_to_depth(
                inputs, temporal_block_size=self.temporal_downsample, spatial_block_size=self.spatial_downsample
            )

            if inputs.ndim == 5 and inputs.shape[1] == 1:
                # for flow
                inputs = inputs.squeeze(dim=1)

            # Optionally apply conv layer.
            inputs = self.conv_after_patches(inputs)

        if self.prep_type != "patches":
            # move channels to last dimension, as the _build_network_inputs method below expects this
            if inputs.ndim == 4:
                inputs = torch.moveaxis(inputs, 1, -1)
            elif inputs.ndim == 5:
                inputs = torch.moveaxis(inputs, 2, -1)
            else:
                raise ValueError("Unsupported data format for conv1x1.")

        inputs, inputs_without_pos = self._build_network_inputs(inputs, pos, network_input_is_1d)
        modality_sizes = None  # Size for each modality, only needed for multimodal

        return inputs, modality_sizes, inputs_without_pos


class PerceiverOneHotPreprocessor(AbstractPreprocessor):
    """
    One-hot preprocessor for Perceiver Encoder. Can be used to add a dummy index dimension to the input.

    Args:
        config ([`PerceiverConfig`]):
            Model configuration.
    """

    def __init__(self, config):
        super().__init__()
        self.config: PerceiverConfig = config

    @property
    def num_channels(self) -> int:
        return self.config.num_labels

    def forward(self, inputs: torch.Tensor, pos: Optional[torch.Tensor] = None, network_input_is_1d: bool = True):
        # Add a dummy index dimension.
        inputs = inputs[:, None, :]

        # No position encodings, so the 1st (input) and 3rd (inputs_without_pos)
        # outputs are identical.
        return inputs, None, inputs


class PerceiverAudioPreprocessor(AbstractPreprocessor):
    """
    Audio preprocessing for Perceiver Encoder.

    Args:
        config ([`PerceiverConfig`]):
            Model configuration.
        prep_type (:obj:`str`, `optional`, defaults to :obj:`"patches"`):
            Preprocessor type to use. Only "patches" is supported.
        samples_per_patch (:obj:`int`, `optional`, defaults to 96):
            Number of samples per patch.
        position_encoding_type (:obj:`str`, `optional`, defaults to :obj:`"fourier"`):
            Type of position encoding to use. Can be "trainable" or "fourier".
        concat_or_add_pos (:obj:`str`, `optional`, defaults to :obj:`"concat"`):
            How to concatenate the position encoding to the input. Can be "concat" or "add".
        out_channels (:obj:`int`, `optional`, defaults to 64):
            Number of channels in the output.
        project_pos_dim (:obj:`int`, `optional`, defaults to -1):
            Dimension of the position encoding to project to. If -1, no projection is applied.
        **position_encoding_kwargs (:obj:`Dict`, `optional`):
            Keyword arguments for the position encoding.
    """

    def __init__(
        self,
        config,
        prep_type: str = "patches",
        samples_per_patch: int = 96,
        position_encoding_type: str = "fourier",
        concat_or_add_pos: str = "concat",
        out_channels=64,
        project_pos_dim=-1,
        **position_encoding_kwargs,
    ):
        super().__init__()
        self.config = config

        if prep_type not in ("patches",):
            raise ValueError(f"Prep_type {prep_type} is invalid, can only be 'patches'.")

        if concat_or_add_pos not in ["concat", "add"]:
            raise ValueError(f"Concat_or_pos {concat_or_add_pos} is invalid, can only be 'concat' or 'add'.")

        self.samples_per_patch = samples_per_patch
        self.position_encoding_type = position_encoding_type
        self.concat_or_add_pos = concat_or_add_pos
        self.project_pos_dim = project_pos_dim

        # Position embeddings
        self.position_embeddings, self.positions_projection = build_position_encoding(
            position_encoding_type=position_encoding_type,
            out_channels=out_channels,
            project_pos_dim=project_pos_dim,
            **position_encoding_kwargs,
        )

    @property
    def num_channels(self) -> int:
        # position embedding
        if self.project_pos_dim > 0:
            pos_dim = self.project_pos_dim
        else:
            pos_dim = self.position_embeddings.output_size()
        if self.concat_or_add_pos == "add":
            return pos_dim
        return self.samples_per_patch + pos_dim

    def _build_network_inputs(self, inputs, pos):
        """Construct the final input, including position encoding."""
        batch_size = inputs.shape[0]
        index_dims = inputs.shape[1:-1]

        # Construct the position encoding.
        if self.position_encoding_type == "trainable":
            pos_enc = self.position_embeddings(batch_size)
        elif self.position_encoding_type == "fourier":
            pos_enc = self.position_embeddings(index_dims, batch_size, device=inputs.device)

        # Optionally project them to a target dimension.
        pos_enc = self.positions_projection(pos_enc)

        if self.concat_or_add_pos == "concat":
            inputs_with_pos = torch.cat([inputs, pos_enc], dim=-1)
        elif self.concat_or_add_pos == "add":
            inputs_with_pos = inputs + pos_enc

        return inputs_with_pos, inputs

    def forward(self, inputs, pos, network_input_is_1d: bool = True):
        inputs = torch.reshape(inputs, [inputs.shape[0], -1, self.samples_per_patch])

        inputs, inputs_without_pos = self._build_network_inputs(inputs, pos)
        modality_sizes = None  # Size for each modality, only needed for multimodal

        return inputs, modality_sizes, inputs_without_pos


class PerceiverMultimodalPreprocessor(AbstractPreprocessor):
    """
    Multimodal preprocessing for Perceiver Encoder.

    Inputs for each modality are preprocessed, then padded with trainable position embeddings to have the same number
    of channels.

    Args:
        modalities (:obj:`Dict[str, PreprocessorType]`):
            Dict mapping modality name to preprocessor.
        mask_probs (:obj:`Dict[str, float]`):
            Dict mapping modality name to masking probability of that modality.
        min_padding_size (:obj:`int`, `optional`, defaults to 2):
            The minimum padding size for all modalities. The final output will have num_channels equal to the maximum
            channels across all modalities plus min_padding_size.
    """

    def __init__(
        self,
        modalities: Mapping[str, PreprocessorType],
        mask_probs: Optional[Mapping[str, float]] = None,
        min_padding_size: int = 2,
    ):
        super().__init__()
        self.modalities = modalities
        self.min_padding_size = min_padding_size
        self.mask_probs = mask_probs if mask_probs is not None else dict()
        self.padding = nn.ParameterDict(
            {
                modality: nn.Parameter(torch.randn(1, self.num_channels - preprocessor.num_channels))
                for modality, preprocessor in modalities.items()
            }
        )
        self.mask = nn.ParameterDict(
            {modality: nn.Parameter(torch.randn(1, self.num_channels)) for modality, _ in self.mask_probs.items()}
        )

    @property
    def num_channels(self) -> int:
        max_channel_size = max(processor.num_channels for _, processor in self.modalities.items())
        common_channel_size = max_channel_size + self.min_padding_size
        return common_channel_size

    def forward(
        self, inputs: Mapping[str, torch.Tensor], pos: Optional[torch.Tensor] = None, network_input_is_1d: bool = True
    ) -> PreprocessorOutputType:
        padded = {}
        modality_sizes = {}
        inputs_without_pos = {}
        for modality, preprocessor in self.modalities.items():
            # preprocess each modality using the respective preprocessor.
            output, _, inputs_without_pos[modality] = preprocessor(
                inputs[modality], pos=pos, network_input_is_1d=network_input_is_1d
            )

            # pad to the same common_channel_size.
            batch_size, num_samples, num_channels = output.shape
            pos_enc = self.padding[modality].expand(batch_size, -1, -1)

            padding = torch.broadcast_to(
                pos_enc,
                [batch_size, num_samples, self.num_channels - num_channels],
            )
            output_padded = torch.cat([output, padding], dim=2)

            # mask if required
            if modality in self.mask_probs:
                mask_token = self.mask[modality].expand(batch_size, -1, -1)
                mask_prob = self.mask_probs[modality]
                mask = torch.bernoulli(torch.full([batch_size, num_samples], mask_prob))
                mask = torch.unsqueeze(mask, dim=2).to(mask_token.device)
                output_padded = (1 - mask) * output_padded + mask * mask_token

            padded[modality] = output_padded
            modality_sizes[modality] = output_padded.shape[1]

        # Apply a predictable ordering to the modalities
        padded_ls = [padded[k] for k in sorted(padded.keys())]

        # Finally, concatenate along the time dimension
        final_inputs = torch.cat(padded_ls, dim=1)

        return final_inputs, modality_sizes, inputs_without_pos
