# standard imports
from functools import partial
import contextlib
import io
import os
import shutil
import tempfile
import typing

# external imports
from preview_generator.manager import PreviewManager
import PIL.Image

# bsie imports
from bsie.utils import errors

# inner-module imports
from .. import base

# exports
__all__: typing.Sequence[str] = (
    'PreviewGeneratorReader',
    )


## code ##

class PreviewGeneratorReader(base.Reader):
    """Uses preview_generator to create previews for various data formats.
    See `https://github.com/algoo/preview-generator`_ for details.
    """

    # PreviewManager instance.
    _mngr: PreviewManager

    # Set of mime types supported by PreviewManager.
    _supported_mimetypes: typing.Set[str]

    # PreviewManager cache.
    _cache: str

    # Determines whether the cache directory should be deleted after use.
    _cleanup: bool

    def __init__(self, cache: typing.Optional[str] = None):
        # initialize cache directory
        # TODO: initialize in memory, e.g., via PyFilesystem
        if cache is None:
            self._cache = tempfile.mkdtemp(prefix='bsie-preview-cache-')
            self._cleanup = True
        else:
            self._cache = cache
            self._cleanup = False
        # create preview generator
        with contextlib.redirect_stderr(io.StringIO()):
            self._mngr = PreviewManager(self._cache, create_folder=True)
        self._supported_mimetypes = set(self._mngr.get_supported_mimetypes())

    def __del__(self):
        if self._cleanup:
            shutil.rmtree(self._cache, ignore_errors=True)

    def __call__(self, path: str) -> typing.Callable[[int], PIL.Image.Image]:
        if not os.path.exists(path):
            raise errors.ReaderError(path)
        if self._mngr.get_mimetype(path) not in self._supported_mimetypes:
            raise errors.UnsupportedFileFormatError(path)
        return partial(self._preview_callback, path)

    def _preview_callback(self, path: str, max_side: int) -> PIL.Image.Image:
        """Produce a jpeg preview of *path* with at most *max_side* side length."""
        try:
            # generate the preview
            preview_path = self._mngr.get_jpeg_preview(path, width=max_side, height=max_side)
            # open the preview and return
            return PIL.Image.open(preview_path)
        except Exception as err: # FIXME: less generic exception!
            raise errors.ReaderError(path) from err

## EOF ##