1 files changed, 86 insertions, 0 deletions
diff --git a/bsie/reader/preview/_pg.py b/bsie/reader/preview/_pg.py
new file mode 100644
index 0000000..097c513
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+++ b/bsie/reader/preview/_pg.py
@@ -0,0 +1,86 @@
+"""
+
+Part of the bsie module.
+A copy of the license is provided with the project.
+Author: Matthias Baumgartner, 2022
+"""
+# 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 ##