import sys
from ast import (
    AsyncFunctionDef,
    FunctionDef,
)
from collections import deque
from os.path import isabs
from types import FrameType
from typing import Any, Callable, Optional, cast

from defer.errors import FreeVarsError
from defer.sugar.transformer import RewriteDefer


def _is_dunder(name: str) -> bool:
    return name.startswith("__") and name.endswith("__")


def _is_excluded_path(filename: str) -> bool:
    if not filename:
        return True
    return (
        filename.startswith(sys.base_exec_prefix)
        or filename.startswith(sys.base_prefix)
        or filename.startswith(sys.exec_prefix)
        or filename.startswith(sys.prefix)
        or ".venv" in filename
        or filename.startswith("<frozen ")
        or filename.startswith("<string>")
        or filename.startswith("<pytest ")
        or "thirdparty" in filename
        or "__future__" in filename
    )


class _ParseDefer:
    IDENTITY = lambda *_: None  # noqa: E731

    def __init__(self, tracefn: Optional[Callable]) -> None:
        self.tracefn = tracefn or self.IDENTITY
        self.pending: deque[Executing] = deque()

    def __call__(self, frame: FrameType, event: str, arg: Any):
        try:
            self._do_call(frame, event, arg)
        except Exception:
            pass
        return self

    def _do_call(self, frame: FrameType, event: str, arg: Any):
        self.tracefn(frame, event, arg)

        try:
            filename = frame.f_code.co_filename
        except Exception:
            return

        if _is_excluded_path(filename):
            return

        if not isabs(filename):
            return

        if event != "line":
            return

        try:
            from executing.executing import Executing, Source
        except ImportError:
            return

        try:
            exc = Source.executing(frame)
        except Exception:
            return

        if not (stmt := next(iter(exc.statements), None)):
            return
        if isinstance(stmt, (AsyncFunctionDef, FunctionDef)):
            if _is_dunder(stmt.name):
                return
            self.pending.append(exc)
            return
        if not self.pending or frame.f_back is not self.pending[-1].frame.f_back:
            return

        stmts = self.pending.pop().statements
        node = cast(FunctionDef | AsyncFunctionDef, next(iter(stmts)))
        fn_name = node.name

        if fn_name not in frame.f_locals:
            return
        fn = frame.f_locals[fn_name]

        if fn.__module__ in sys.stdlib_module_names:
            return
        if fn.__code__.co_freevars:
            raise FreeVarsError(fn)
        if not (ast := RewriteDefer.transform(node)):
            return

        locals = frame.f_locals.copy()
        del locals[fn_name]
        exec(compile(ast, frame.f_code.co_filename, "exec"), frame.f_globals, locals)
        frame.f_locals[fn_name].__code__ = locals[fn_name].__code__