import os
import pathlib
import tempfile
import functools
import contextlib
import types
import importlib
import inspect
import itertools

from typing import Union, Optional, cast
from .abc import ResourceReader, Traversable

Package = Union[types.ModuleType, str]
Anchor = Package


def files(anchor: Optional[Anchor] = None) -> Traversable:
    """
    Get a Traversable resource for an anchor.
    """
    return from_package(resolve(anchor))


def get_resource_reader(package: types.ModuleType) -> Optional[ResourceReader]:
    """
    Return the package's loader if it's a ResourceReader.
    """
    # We can't use
    # a issubclass() check here because apparently abc.'s __subclasscheck__()
    # hook wants to create a weak reference to the object, but
    # zipimport.zipimporter does not support weak references, resulting in a
    # TypeError.  That seems terrible.
    spec = package.__spec__
    reader = getattr(spec.loader, 'get_resource_reader', None)  # type: ignore[union-attr]
    if reader is None:
        return None
    return reader(spec.name)  # type: ignore[union-attr]


@functools.singledispatch
def resolve(cand: Optional[Anchor]) -> types.ModuleType:
    return cast(types.ModuleType, cand)


@resolve.register
def _(cand: str) -> types.ModuleType:
    return importlib.import_module(cand)


@resolve.register
def _(cand: None) -> types.ModuleType:
    return resolve(_infer_caller().f_globals['__name__'])


def _infer_caller():
    """
    Walk the stack and find the frame of the first caller not in this module.
    """

    def is_this_file(frame_info):
        return frame_info.filename == stack[0].filename

    def is_wrapper(frame_info):
        return frame_info.function == 'wrapper'

    stack = inspect.stack()
    not_this_file = itertools.filterfalse(is_this_file, stack)
    # also exclude 'wrapper' due to singledispatch in the call stack
    callers = itertools.filterfalse(is_wrapper, not_this_file)
    return next(callers).frame


def from_package(package: types.ModuleType):
    """
    Return a Traversable object for the given package.

    """
    # deferred for performance (python/cpython#109829)
    from ._adapters import wrap_spec

    spec = wrap_spec(package)
    reader = spec.loader.get_resource_reader(spec.name)
    return reader.files()


@contextlib.contextmanager
def _tempfile(
    reader,
    suffix='',
    # gh-93353: Keep a reference to call os.remove() in late Python
    # finalization.
    *,
    _os_remove=os.remove,
):
    # Not using tempfile.NamedTemporaryFile as it leads to deeper 'try'
    # blocks due to the need to close the temporary file to work on Windows
    # properly.
    fd, raw_path = tempfile.mkstemp(suffix=suffix)
    try:
        try:
            os.write(fd, reader())
        finally:
            os.close(fd)
        del reader
        yield pathlib.Path(raw_path)
    finally:
        try:
            _os_remove(raw_path)
        except FileNotFoundError:
            pass


def _temp_file(path):
    return _tempfile(path.read_bytes, suffix=path.name)


def _is_present_dir(path: Traversable) -> bool:
    """
    Some Traversables implement ``is_dir()`` to raise an
    exception (i.e. ``FileNotFoundError``) when the
    directory doesn't exist. This function wraps that call
    to always return a boolean and only return True
    if there's a dir and it exists.
    """
    with contextlib.suppress(FileNotFoundError):
        return path.is_dir()
    return False


@functools.singledispatch
def as_file(path):
    """
    Given a Traversable object, return that object as a
    path on the local file system in a context manager.
    """
    return _temp_dir(path) if _is_present_dir(path) else _temp_file(path)


@as_file.register(pathlib.Path)
@contextlib.contextmanager
def _(path):
    """
    Degenerate behavior for pathlib.Path objects.
    """
    yield path


@contextlib.contextmanager
def _temp_path(dir: tempfile.TemporaryDirectory):
    """
    Wrap tempfile.TemporaryDirectory to return a pathlib object.
    """
    with dir as result:
        yield pathlib.Path(result)


@contextlib.contextmanager
def _temp_dir(path):
    """
    Given a traversable dir, recursively replicate the whole tree
    to the file system in a context manager.
    """
    assert path.is_dir()
    with _temp_path(tempfile.TemporaryDirectory()) as temp_dir:
        yield _write_contents(temp_dir, path)


def _write_contents(target, source):
    child = target.joinpath(source.name)
    if source.is_dir():
        child.mkdir()
        for item in source.iterdir():
            _write_contents(child, item)
    else:
        child.write_bytes(source.read_bytes())
    return child
