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# 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 ##
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