group thumbnailers in categories so they can be enabled selectively

An app using vignette could want to only keep a category of handled
files. See #4

vignette/__init__.py

@@ -187,6 +187,10 @@
 	'KEY_MIME',
 	'KEY_DOC_PAGES',
 	'KEY_MOVIE_LENGTH',
+	'select_thumbnailer_types',
+	'FILETYPE_IMAGE',
+	'FILETYPE_VIDEO',
+	'FILETYPE_DOCUMENT',
 )
 
 if sys.version_info.major == 2:
@@ -469,6 +473,11 @@ def update_metadata(self, dest, moreinfo=None):
 		raise NotImplementedError()
 
 
+FILETYPE_IMAGE = 'image'
+FILETYPE_VIDEO = 'video'
+FILETYPE_DOCUMENT = 'document'
+
+
 class ThumbnailBackend(object):
 	def is_available(self):
 		return False
@@ -478,6 +487,8 @@ def create_thumbnail(self, src, dest, size):
 
 
 class PilBackend(MetadataBackend, ThumbnailBackend):
+	handled_types = frozenset([FILETYPE_IMAGE])
+
 	@classmethod
 	def is_available(cls):
 		try:
@@ -554,6 +565,8 @@ def update_metadata(self, dest, moreinfo=None):
 
 
 class MagickBackend(MetadataBackend, ThumbnailBackend):
+	handled_types = frozenset([FILETYPE_IMAGE])
+
 	@classmethod
 	def is_available(cls):
 		try:
@@ -636,6 +649,7 @@ def is_available(self):
 
 
 class PopplerCliBackend(CliMixin, ThumbnailBackend):
+	handled_types = frozenset([FILETYPE_DOCUMENT])
 	cmd = 'pdftocairo'
 
 	def create_thumbnail(self, src, dest, size):
@@ -649,6 +663,7 @@ def create_thumbnail(self, src, dest, size):
 
 
 class OooCliBackend(CliMixin, ThumbnailBackend):
+	handled_types = frozenset([FILETYPE_DOCUMENT])
 	cmd = 'ooo-thumbnailer'
 
 	def create_thumbnail(self, src, dest, size):
@@ -663,6 +678,8 @@ def create_thumbnail(self, src, dest, size):
 
 
 class QtBackend(MetadataBackend, ThumbnailBackend):
+	handled_types = frozenset([FILETYPE_IMAGE])
+
 	@classmethod
 	def is_available(cls):
 		try:
@@ -737,12 +754,27 @@ def get_info(self, path):
 
 
 class GnomeThumbnailer(CliMixin, ThumbnailBackend):
+	mime_to_handle = {
+		re.compile('^image/'): FILETYPE_IMAGE,
+		re.compile('^video/'): FILETYPE_VIDEO,
+		re.compile('^application/pdf'): FILETYPE_DOCUMENT,
+		re.compile('^application/vnd.oasis.opendocument.'): FILETYPE_DOCUMENT,
+		re.compile('^application/vnd.openxmlformats-officedocument.'): FILETYPE_DOCUMENT,
+	}
+
 	def __init__(self, cmd_test, cmd_exec, mimes):
 		self.cmd = cmd_test
 		self.accepted_mimes = re.compile('^(?:%s)$' % '|'.join(map(re.escape, mimes)))
 		cmd_exec = re.sub('%([iosu])', r'%(\1)s', cmd_exec)
 		self.cmd_exec = shlex.split(cmd_exec)
 
+		self.handled_types = set()
+		for mime in mimes:
+			for reobj, const in self.mime_to_handle.items():
+				if reobj.match(mime):
+					self.handled_types.add(const)
+					break
+
 	def __repr__(self):
 		return '<%s cmd=%r>' % (type(self).__name__, self.cmd)
 
@@ -782,15 +814,17 @@ def build_gnome_thumbnailers():
 
 METADATA_BACKENDS = [QtBackend(), PilBackend(), MagickBackend()]
 
-THUMBNAILER_BACKENDS = [
+ALL_THUMBNAILER_BACKENDS = [
 	OooCliBackend(),
 	PopplerCliBackend(),
 	QtBackend(),
 	PilBackend(),
 	MagickBackend()
 ]
 
-THUMBNAILER_BACKENDS.extend(build_gnome_thumbnailers())
+ALL_THUMBNAILER_BACKENDS.extend(build_gnome_thumbnailers())
+
+THUMBNAILER_BACKENDS = list(ALL_THUMBNAILER_BACKENDS)
 
 
 def get_metadata_backend():
@@ -949,6 +983,21 @@ def thumbnail_info(thumbnail):
 	return get_metadata_backend().get_info(thumbnail)
 
 
+def select_thumbnailer_types(types):
+	"""Select a subset of thumbnailer backends, by type of handled file.
+
+	:param types: iterable containing constants `FILETYPE_*`
+	"""
+	global THUMBNAILER_BACKENDS
+
+	if isinstance(types, (bytes, str)):
+		types = (types,)
+	THUMBNAILER_BACKENDS = [
+		b for b in ALL_THUMBNAILER_BACKENDS
+		if b.handled_types & set(types)
+	]
+
+
 def main():
 	output = get_thumbnail(sys.argv[1])
 	if output is None: