"""
NRT specific optimizations
"""
import re
from collections import defaultdict, deque
from llvmlite import binding as ll

_regex_incref = re.compile(r'\s*(?:tail)?\s*call void @NRT_incref\((.*)\)')
_regex_decref = re.compile(r'\s*(?:tail)?\s*call void @NRT_decref\((.*)\)')
_regex_bb = re.compile(r'([\'"]?[-a-zA-Z$._][-a-zA-Z$._0-9]*[\'"]?:)|^define')


def _remove_redundant_nrt_refct(llvmir):
    # Note: As soon as we have better utility in analyzing materialized LLVM
    #       module in llvmlite, we can redo this without so much string
    #       processing.
    def _extract_functions(module):
        cur = []
        for line in str(module).splitlines():
            if line.startswith('define'):
                # start of function
                assert not cur
                cur.append(line)
            elif line.startswith('}'):
                # end of function
                assert cur
                cur.append(line)
                yield True, cur
                cur = []
            elif cur:
                cur.append(line)
            else:
                yield False, [line]

    def _process_function(func_lines):
        out = []
        for is_bb, bb_lines in _extract_basic_blocks(func_lines):
            if is_bb and bb_lines:
                bb_lines = _process_basic_block(bb_lines)
            out += bb_lines
        return out

    def _extract_basic_blocks(func_lines):
        assert func_lines[0].startswith('define')
        assert func_lines[-1].startswith('}')
        yield False, [func_lines[0]]

        cur = []
        for ln in func_lines[1:-1]:
            m = _regex_bb.match(ln)
            if m is not None:
                # line is a basic block separator
                yield True, cur
                cur = []
                yield False, [ln]
            elif ln:
                cur.append(ln)

        yield True, cur
        yield False, [func_lines[-1]]

    def _process_basic_block(bb_lines):
        bb_lines = _move_and_group_decref_after_all_increfs(bb_lines)
        bb_lines = _prune_redundant_refct_ops(bb_lines)
        return bb_lines

    def _examine_refct_op(bb_lines):
        for num, ln in enumerate(bb_lines):
            m = _regex_incref.match(ln)
            if m is not None:
                yield num, m.group(1), None
                continue

            m = _regex_decref.match(ln)
            if m is not None:
                yield num, None, m.group(1)
                continue

            yield ln, None, None

    def _prune_redundant_refct_ops(bb_lines):
        incref_map = defaultdict(deque)
        decref_map = defaultdict(deque)
        to_remove = set()
        for num, incref_var, decref_var in _examine_refct_op(bb_lines):
            assert not (incref_var and decref_var)
            if incref_var:
                if incref_var == 'i8* null':
                    to_remove.add(num)
                else:
                    incref_map[incref_var].append(num)
            elif decref_var:
                if decref_var == 'i8* null':
                    to_remove.add(num)
                else:
                    decref_map[decref_var].append(num)

        for var, decops in decref_map.items():
            incops = incref_map[var]
            ct = min(len(incops), len(decops))
            for _ in range(ct):
                to_remove.add(incops.pop())
                to_remove.add(decops.popleft())

        return [ln for num, ln in enumerate(bb_lines)
                if num not in to_remove]

    def _move_and_group_decref_after_all_increfs(bb_lines):
        # find last incref
        last_incref_pos = 0
        for pos, ln in enumerate(bb_lines):
            if _regex_incref.match(ln) is not None:
                last_incref_pos = pos + 1

        # find last decref
        last_decref_pos = 0
        for pos, ln in enumerate(bb_lines):
            if _regex_decref.match(ln) is not None:
                last_decref_pos = pos + 1

        last_pos = max(last_incref_pos, last_decref_pos)

        # find decrefs before last_pos
        decrefs = []
        head = []
        for ln in bb_lines[:last_pos]:
            if _regex_decref.match(ln) is not None:
                decrefs.append(ln)
            else:
                head.append(ln)

        # insert decrefs at last_pos
        return head + decrefs + bb_lines[last_pos:]

    # Driver
    processed = []

    for is_func, lines in _extract_functions(llvmir):
        if is_func:
            lines = _process_function(lines)

        processed += lines

    return '\n'.join(processed)


def remove_redundant_nrt_refct(ll_module):
    """
    Remove redundant reference count operations from the
    `llvmlite.binding.ModuleRef`. This parses the ll_module as a string and
    line by line to remove the unnecessary nrt refct pairs within each block.
    Decref calls are moved after the last incref call in the block to avoid
    temporarily decref'ing to zero (which can happen due to hidden decref from
    alias).

    Note: non-threadsafe due to usage of global LLVMcontext
    """
    # Early escape if NRT_incref is not used
    try:
        ll_module.get_function('NRT_incref')
    except NameError:
        return ll_module

    newll = _remove_redundant_nrt_refct(str(ll_module))
    return ll.parse_assembly(newll)
