import numbers
from typing import TYPE_CHECKING, Dict, List, Optional, Tuple, Type, Union
import warnings

import numpy as np

from pandas._libs import lib, missing as libmissing
from pandas._typing import ArrayLike, DtypeObj
from pandas.compat import set_function_name
from pandas.compat.numpy import function as nv
from pandas.util._decorators import cache_readonly

from pandas.core.dtypes.base import register_extension_dtype
from pandas.core.dtypes.common import (
    is_bool_dtype,
    is_datetime64_dtype,
    is_float,
    is_float_dtype,
    is_integer,
    is_integer_dtype,
    is_list_like,
    is_object_dtype,
    pandas_dtype,
)
from pandas.core.dtypes.missing import isna

from pandas.core import ops
from pandas.core.array_algos import masked_reductions
from pandas.core.ops import invalid_comparison
from pandas.core.ops.common import unpack_zerodim_and_defer
from pandas.core.tools.numeric import to_numeric

from .masked import BaseMaskedArray, BaseMaskedDtype

if TYPE_CHECKING:
    import pyarrow  # noqa: F401


class _IntegerDtype(BaseMaskedDtype):
    """
    An ExtensionDtype to hold a single size & kind of integer dtype.

    These specific implementations are subclasses of the non-public
    _IntegerDtype. For example we have Int8Dtype to represent signed int 8s.

    The attributes name & type are set when these subclasses are created.
    """

    name: str
    base = None
    type: Type

    def __repr__(self) -> str:
        sign = "U" if self.is_unsigned_integer else ""
        return f"{sign}Int{8 * self.itemsize}Dtype()"

    @cache_readonly
    def is_signed_integer(self) -> bool:
        return self.kind == "i"

    @cache_readonly
    def is_unsigned_integer(self) -> bool:
        return self.kind == "u"

    @property
    def _is_numeric(self) -> bool:
        return True

    @cache_readonly
    def numpy_dtype(self) -> np.dtype:
        """ Return an instance of our numpy dtype """
        return np.dtype(self.type)

    @cache_readonly
    def kind(self) -> str:
        return self.numpy_dtype.kind

    @cache_readonly
    def itemsize(self) -> int:
        """ Return the number of bytes in this dtype """
        return self.numpy_dtype.itemsize

    @classmethod
    def construct_array_type(cls) -> Type["IntegerArray"]:
        """
        Return the array type associated with this dtype.

        Returns
        -------
        type
        """
        return IntegerArray

    def _get_common_dtype(self, dtypes: List[DtypeObj]) -> Optional[DtypeObj]:
        # we only handle nullable EA dtypes and numeric numpy dtypes
        if not all(
            isinstance(t, BaseMaskedDtype)
            or (
                isinstance(t, np.dtype)
                and (np.issubdtype(t, np.number) or np.issubdtype(t, np.bool_))
            )
            for t in dtypes
        ):
            return None
        np_dtype = np.find_common_type(
            [t.numpy_dtype if isinstance(t, BaseMaskedDtype) else t for t in dtypes], []
        )
        if np.issubdtype(np_dtype, np.integer):
            return _dtypes[str(np_dtype)]
        return None

    def __from_arrow__(
        self, array: Union["pyarrow.Array", "pyarrow.ChunkedArray"]
    ) -> "IntegerArray":
        """
        Construct IntegerArray from pyarrow Array/ChunkedArray.
        """
        import pyarrow  # noqa: F811

        from pandas.core.arrays._arrow_utils import pyarrow_array_to_numpy_and_mask

        pyarrow_type = pyarrow.from_numpy_dtype(self.type)
        if not array.type.equals(pyarrow_type):
            array = array.cast(pyarrow_type)

        if isinstance(array, pyarrow.Array):
            chunks = [array]
        else:
            # pyarrow.ChunkedArray
            chunks = array.chunks

        results = []
        for arr in chunks:
            data, mask = pyarrow_array_to_numpy_and_mask(arr, dtype=self.type)
            int_arr = IntegerArray(data.copy(), ~mask, copy=False)
            results.append(int_arr)

        return IntegerArray._concat_same_type(results)


def integer_array(values, dtype=None, copy: bool = False,) -> "IntegerArray":
    """
    Infer and return an integer array of the values.

    Parameters
    ----------
    values : 1D list-like
    dtype : dtype, optional
        dtype to coerce
    copy : bool, default False

    Returns
    -------
    IntegerArray

    Raises
    ------
    TypeError if incompatible types
    """
    values, mask = coerce_to_array(values, dtype=dtype, copy=copy)
    return IntegerArray(values, mask)


def safe_cast(values, dtype, copy: bool):
    """
    Safely cast the values to the dtype if they
    are equivalent, meaning floats must be equivalent to the
    ints.

    """
    try:
        return values.astype(dtype, casting="safe", copy=copy)
    except TypeError as err:

        casted = values.astype(dtype, copy=copy)
        if (casted == values).all():
            return casted

        raise TypeError(
            f"cannot safely cast non-equivalent {values.dtype} to {np.dtype(dtype)}"
        ) from err


def coerce_to_array(
    values, dtype, mask=None, copy: bool = False,
) -> Tuple[np.ndarray, np.ndarray]:
    """
    Coerce the input values array to numpy arrays with a mask

    Parameters
    ----------
    values : 1D list-like
    dtype : integer dtype
    mask : bool 1D array, optional
    copy : bool, default False
        if True, copy the input

    Returns
    -------
    tuple of (values, mask)
    """
    # if values is integer numpy array, preserve it's dtype
    if dtype is None and hasattr(values, "dtype"):
        if is_integer_dtype(values.dtype):
            dtype = values.dtype

    if dtype is not None:
        if isinstance(dtype, str) and (
            dtype.startswith("Int") or dtype.startswith("UInt")
        ):
            # Avoid DeprecationWarning from NumPy about np.dtype("Int64")
            # https://github.com/numpy/numpy/pull/7476
            dtype = dtype.lower()

        if not issubclass(type(dtype), _IntegerDtype):
            try:
                dtype = _dtypes[str(np.dtype(dtype))]
            except KeyError as err:
                raise ValueError(f"invalid dtype specified {dtype}") from err

    if isinstance(values, IntegerArray):
        values, mask = values._data, values._mask
        if dtype is not None:
            values = values.astype(dtype.numpy_dtype, copy=False)

        if copy:
            values = values.copy()
            mask = mask.copy()
        return values, mask

    values = np.array(values, copy=copy)
    if is_object_dtype(values):
        inferred_type = lib.infer_dtype(values, skipna=True)
        if inferred_type == "empty":
            values = np.empty(len(values))
            values.fill(np.nan)
        elif inferred_type not in [
            "floating",
            "integer",
            "mixed-integer",
            "integer-na",
            "mixed-integer-float",
        ]:
            raise TypeError(f"{values.dtype} cannot be converted to an IntegerDtype")

    elif is_bool_dtype(values) and is_integer_dtype(dtype):
        values = np.array(values, dtype=int, copy=copy)

    elif not (is_integer_dtype(values) or is_float_dtype(values)):
        raise TypeError(f"{values.dtype} cannot be converted to an IntegerDtype")

    if mask is None:
        mask = isna(values)
    else:
        assert len(mask) == len(values)

    if not values.ndim == 1:
        raise TypeError("values must be a 1D list-like")
    if not mask.ndim == 1:
        raise TypeError("mask must be a 1D list-like")

    # infer dtype if needed
    if dtype is None:
        dtype = np.dtype("int64")
    else:
        dtype = dtype.type

    # if we are float, let's make sure that we can
    # safely cast

    # we copy as need to coerce here
    if mask.any():
        values = values.copy()
        values[mask] = 1
        values = safe_cast(values, dtype, copy=False)
    else:
        values = safe_cast(values, dtype, copy=False)

    return values, mask


class IntegerArray(BaseMaskedArray):
    """
    Array of integer (optional missing) values.

    .. versionadded:: 0.24.0

    .. versionchanged:: 1.0.0

       Now uses :attr:`pandas.NA` as the missing value rather
       than :attr:`numpy.nan`.

    .. warning::

       IntegerArray is currently experimental, and its API or internal
       implementation may change without warning.

    We represent an IntegerArray with 2 numpy arrays:

    - data: contains a numpy integer array of the appropriate dtype
    - mask: a boolean array holding a mask on the data, True is missing

    To construct an IntegerArray from generic array-like input, use
    :func:`pandas.array` with one of the integer dtypes (see examples).

    See :ref:`integer_na` for more.

    Parameters
    ----------
    values : numpy.ndarray
        A 1-d integer-dtype array.
    mask : numpy.ndarray
        A 1-d boolean-dtype array indicating missing values.
    copy : bool, default False
        Whether to copy the `values` and `mask`.

    Attributes
    ----------
    None

    Methods
    -------
    None

    Returns
    -------
    IntegerArray

    Examples
    --------
    Create an IntegerArray with :func:`pandas.array`.

    >>> int_array = pd.array([1, None, 3], dtype=pd.Int32Dtype())
    >>> int_array
    <IntegerArray>
    [1, <NA>, 3]
    Length: 3, dtype: Int32

    String aliases for the dtypes are also available. They are capitalized.

    >>> pd.array([1, None, 3], dtype='Int32')
    <IntegerArray>
    [1, <NA>, 3]
    Length: 3, dtype: Int32

    >>> pd.array([1, None, 3], dtype='UInt16')
    <IntegerArray>
    [1, <NA>, 3]
    Length: 3, dtype: UInt16
    """

    # The value used to fill '_data' to avoid upcasting
    _internal_fill_value = 1

    @cache_readonly
    def dtype(self) -> _IntegerDtype:
        return _dtypes[str(self._data.dtype)]

    def __init__(self, values: np.ndarray, mask: np.ndarray, copy: bool = False):
        if not (isinstance(values, np.ndarray) and values.dtype.kind in ["i", "u"]):
            raise TypeError(
                "values should be integer numpy array. Use "
                "the 'pd.array' function instead"
            )
        super().__init__(values, mask, copy=copy)

    @classmethod
    def _from_sequence(cls, scalars, dtype=None, copy: bool = False) -> "IntegerArray":
        return integer_array(scalars, dtype=dtype, copy=copy)

    @classmethod
    def _from_sequence_of_strings(
        cls, strings, dtype=None, copy: bool = False
    ) -> "IntegerArray":
        scalars = to_numeric(strings, errors="raise")
        return cls._from_sequence(scalars, dtype, copy)

    _HANDLED_TYPES = (np.ndarray, numbers.Number)

    def __array_ufunc__(self, ufunc, method: str, *inputs, **kwargs):
        # For IntegerArray inputs, we apply the ufunc to ._data
        # and mask the result.
        if method == "reduce":
            # Not clear how to handle missing values in reductions. Raise.
            raise NotImplementedError("The 'reduce' method is not supported.")
        out = kwargs.get("out", ())

        for x in inputs + out:
            if not isinstance(x, self._HANDLED_TYPES + (IntegerArray,)):
                return NotImplemented

        # for binary ops, use our custom dunder methods
        result = ops.maybe_dispatch_ufunc_to_dunder_op(
            self, ufunc, method, *inputs, **kwargs
        )
        if result is not NotImplemented:
            return result

        mask = np.zeros(len(self), dtype=bool)
        inputs2 = []
        for x in inputs:
            if isinstance(x, IntegerArray):
                mask |= x._mask
                inputs2.append(x._data)
            else:
                inputs2.append(x)

        def reconstruct(x):
            # we don't worry about scalar `x` here, since we
            # raise for reduce up above.

            if is_integer_dtype(x.dtype):
                m = mask.copy()
                return IntegerArray(x, m)
            else:
                x[mask] = np.nan
            return x

        result = getattr(ufunc, method)(*inputs2, **kwargs)
        if isinstance(result, tuple):
            tuple(reconstruct(x) for x in result)
        else:
            return reconstruct(result)

    def _coerce_to_array(self, value) -> Tuple[np.ndarray, np.ndarray]:
        return coerce_to_array(value, dtype=self.dtype)

    def astype(self, dtype, copy: bool = True) -> ArrayLike:
        """
        Cast to a NumPy array or ExtensionArray with 'dtype'.

        Parameters
        ----------
        dtype : str or dtype
            Typecode or data-type to which the array is cast.
        copy : bool, default True
            Whether to copy the data, even if not necessary. If False,
            a copy is made only if the old dtype does not match the
            new dtype.

        Returns
        -------
        ndarray or ExtensionArray
            NumPy ndarray, BooleanArray or IntegerArray with 'dtype' for its dtype.

        Raises
        ------
        TypeError
            if incompatible type with an IntegerDtype, equivalent of same_kind
            casting
        """
        from pandas.core.arrays.masked import BaseMaskedDtype
        from pandas.core.arrays.string_ import StringDtype

        dtype = pandas_dtype(dtype)

        # if the dtype is exactly the same, we can fastpath
        if self.dtype == dtype:
            # return the same object for copy=False
            return self.copy() if copy else self
        # if we are astyping to another nullable masked dtype, we can fastpath
        if isinstance(dtype, BaseMaskedDtype):
            data = self._data.astype(dtype.numpy_dtype, copy=copy)
            # mask is copied depending on whether the data was copied, and
            # not directly depending on the `copy` keyword
            mask = self._mask if data is self._data else self._mask.copy()
            return dtype.construct_array_type()(data, mask, copy=False)
        elif isinstance(dtype, StringDtype):
            return dtype.construct_array_type()._from_sequence(self, copy=False)

        # coerce
        if is_float_dtype(dtype):
            # In astype, we consider dtype=float to also mean na_value=np.nan
            na_value = np.nan
        elif is_datetime64_dtype(dtype):
            na_value = np.datetime64("NaT")
        else:
            na_value = lib.no_default

        return self.to_numpy(dtype=dtype, na_value=na_value, copy=False)

    def _values_for_argsort(self) -> np.ndarray:
        """
        Return values for sorting.

        Returns
        -------
        ndarray
            The transformed values should maintain the ordering between values
            within the array.

        See Also
        --------
        ExtensionArray.argsort
        """
        data = self._data.copy()
        if self._mask.any():
            data[self._mask] = data.min() - 1
        return data

    @classmethod
    def _create_comparison_method(cls, op):
        op_name = op.__name__

        @unpack_zerodim_and_defer(op.__name__)
        def cmp_method(self, other):
            from pandas.arrays import BooleanArray

            mask = None

            if isinstance(other, (BooleanArray, IntegerArray)):
                other, mask = other._data, other._mask

            elif is_list_like(other):
                other = np.asarray(other)
                if other.ndim > 1:
                    raise NotImplementedError(
                        "can only perform ops with 1-d structures"
                    )
                if len(self) != len(other):
                    raise ValueError("Lengths must match to compare")

            if other is libmissing.NA:
                # numpy does not handle pd.NA well as "other" scalar (it returns
                # a scalar False instead of an array)
                # This may be fixed by NA.__array_ufunc__. Revisit this check
                # once that's implemented.
                result = np.zeros(self._data.shape, dtype="bool")
                mask = np.ones(self._data.shape, dtype="bool")
            else:
                with warnings.catch_warnings():
                    # numpy may show a FutureWarning:
                    #     elementwise comparison failed; returning scalar instead,
                    #     but in the future will perform elementwise comparison
                    # before returning NotImplemented. We fall back to the correct
                    # behavior today, so that should be fine to ignore.
                    warnings.filterwarnings("ignore", "elementwise", FutureWarning)
                    with np.errstate(all="ignore"):
                        method = getattr(self._data, f"__{op_name}__")
                        result = method(other)

                    if result is NotImplemented:
                        result = invalid_comparison(self._data, other, op)

            # nans propagate
            if mask is None:
                mask = self._mask.copy()
            else:
                mask = self._mask | mask

            return BooleanArray(result, mask)

        name = f"__{op.__name__}__"
        return set_function_name(cmp_method, name, cls)

    def sum(self, skipna=True, min_count=0, **kwargs):
        nv.validate_sum((), kwargs)
        result = masked_reductions.sum(
            values=self._data, mask=self._mask, skipna=skipna, min_count=min_count
        )
        return result

    def _maybe_mask_result(self, result, mask, other, op_name: str):
        """
        Parameters
        ----------
        result : array-like
        mask : array-like bool
        other : scalar or array-like
        op_name : str
        """
        # if we have a float operand we are by-definition
        # a float result
        # or our op is a divide
        if (is_float_dtype(other) or is_float(other)) or (
            op_name in ["rtruediv", "truediv"]
        ):
            result[mask] = np.nan
            return result

        return type(self)(result, mask, copy=False)

    @classmethod
    def _create_arithmetic_method(cls, op):
        op_name = op.__name__

        @unpack_zerodim_and_defer(op.__name__)
        def integer_arithmetic_method(self, other):

            omask = None

            if getattr(other, "ndim", 0) > 1:
                raise NotImplementedError("can only perform ops with 1-d structures")

            if isinstance(other, IntegerArray):
                other, omask = other._data, other._mask

            elif is_list_like(other):
                other = np.asarray(other)
                if other.ndim > 1:
                    raise NotImplementedError(
                        "can only perform ops with 1-d structures"
                    )
                if len(self) != len(other):
                    raise ValueError("Lengths must match")
                if not (is_float_dtype(other) or is_integer_dtype(other)):
                    raise TypeError("can only perform ops with numeric values")

            else:
                if not (is_float(other) or is_integer(other) or other is libmissing.NA):
                    raise TypeError("can only perform ops with numeric values")

            if omask is None:
                mask = self._mask.copy()
                if other is libmissing.NA:
                    mask |= True
            else:
                mask = self._mask | omask

            if op_name == "pow":
                # 1 ** x is 1.
                mask = np.where((self._data == 1) & ~self._mask, False, mask)
                # x ** 0 is 1.
                if omask is not None:
                    mask = np.where((other == 0) & ~omask, False, mask)
                elif other is not libmissing.NA:
                    mask = np.where(other == 0, False, mask)

            elif op_name == "rpow":
                # 1 ** x is 1.
                if omask is not None:
                    mask = np.where((other == 1) & ~omask, False, mask)
                elif other is not libmissing.NA:
                    mask = np.where(other == 1, False, mask)
                # x ** 0 is 1.
                mask = np.where((self._data == 0) & ~self._mask, False, mask)

            if other is libmissing.NA:
                result = np.ones_like(self._data)
            else:
                with np.errstate(all="ignore"):
                    result = op(self._data, other)

            # divmod returns a tuple
            if op_name == "divmod":
                div, mod = result
                return (
                    self._maybe_mask_result(div, mask, other, "floordiv"),
                    self._maybe_mask_result(mod, mask, other, "mod"),
                )

            return self._maybe_mask_result(result, mask, other, op_name)

        name = f"__{op.__name__}__"
        return set_function_name(integer_arithmetic_method, name, cls)


IntegerArray._add_arithmetic_ops()
IntegerArray._add_comparison_ops()


_dtype_docstring = """
An ExtensionDtype for {dtype} integer data.

.. versionchanged:: 1.0.0

   Now uses :attr:`pandas.NA` as its missing value,
   rather than :attr:`numpy.nan`.

Attributes
----------
None

Methods
-------
None
"""

# create the Dtype


@register_extension_dtype
class Int8Dtype(_IntegerDtype):
    type = np.int8
    name = "Int8"
    __doc__ = _dtype_docstring.format(dtype="int8")


@register_extension_dtype
class Int16Dtype(_IntegerDtype):
    type = np.int16
    name = "Int16"
    __doc__ = _dtype_docstring.format(dtype="int16")


@register_extension_dtype
class Int32Dtype(_IntegerDtype):
    type = np.int32
    name = "Int32"
    __doc__ = _dtype_docstring.format(dtype="int32")


@register_extension_dtype
class Int64Dtype(_IntegerDtype):
    type = np.int64
    name = "Int64"
    __doc__ = _dtype_docstring.format(dtype="int64")


@register_extension_dtype
class UInt8Dtype(_IntegerDtype):
    type = np.uint8
    name = "UInt8"
    __doc__ = _dtype_docstring.format(dtype="uint8")


@register_extension_dtype
class UInt16Dtype(_IntegerDtype):
    type = np.uint16
    name = "UInt16"
    __doc__ = _dtype_docstring.format(dtype="uint16")


@register_extension_dtype
class UInt32Dtype(_IntegerDtype):
    type = np.uint32
    name = "UInt32"
    __doc__ = _dtype_docstring.format(dtype="uint32")


@register_extension_dtype
class UInt64Dtype(_IntegerDtype):
    type = np.uint64
    name = "UInt64"
    __doc__ = _dtype_docstring.format(dtype="uint64")


_dtypes: Dict[str, _IntegerDtype] = {
    "int8": Int8Dtype(),
    "int16": Int16Dtype(),
    "int32": Int32Dtype(),
    "int64": Int64Dtype(),
    "uint8": UInt8Dtype(),
    "uint16": UInt16Dtype(),
    "uint32": UInt32Dtype(),
    "uint64": UInt64Dtype(),
}
