Add a "filtered" event

Add a filtered event to apply postprocessing (python/metadata) to posts
that have been excluded from download by the filtering rules
(image and chapter filters).

The goal is to do analysis on filtered content in order to feed a blacklist.

docs/configuration.rst

@@ -6327,6 +6327,9 @@ Description
     ``prepare-after``
         Before a file download,
         but after building and checking file paths
+    ``filtered``
+        When a file has been excluded from download
+        by image-filter or chapter-filter
     ``file``
         When completing a file download,
         but before it gets moved to its target location

gallery_dl/job.py

@@ -44,6 +44,7 @@ def __init__(self, extr, parent=None):
         self.extractor = extr
         self.pathfmt = None
         self.status = 0
+        self.hooks = ()
         self.kwdict = {}
         self.kwdict_eval = False
 
@@ -188,13 +189,20 @@ def run(self):
 
     def dispatch(self, msg):
         """Call the appropriate message handler"""
+        hooks = self.hooks
+        pathfmt = self.pathfmt
+
         if msg[0] == Message.Url:
             _, url, kwdict = msg
             if self.metadata_url:
                 kwdict[self.metadata_url] = url
             if self.pred_url(url, kwdict):
                 self.update_kwdict(kwdict)
                 self.handle_url(url, kwdict)
+            else:
+                if "filtered" in hooks:
+                    for callback in hooks["filtered"]:
+                        callback(pathfmt)
 
         elif msg[0] == Message.Directory:
             self.update_kwdict(msg[1])
@@ -206,6 +214,10 @@ def dispatch(self, msg):
                 kwdict[self.metadata_url] = url
             if self.pred_queue(url, kwdict):
                 self.handle_queue(url, kwdict)
+            else:
+                if "filtered" in hooks:
+                    for callback in hooks["filtered"]:
+                        callback(pathfmt)
 
     def handle_url(self, url, kwdict):
         """Handle Message.Url"""

gallery_dl/option.py

@@ -171,8 +171,9 @@ def __call__(self, parser, namespace, value, option_string=None):
         else:
             event = event.strip().lower()
             if event not in {"init", "file", "after", "skip", "error",
-                             "prepare", "prepare-after", "post", "post-after",
-                             "finalize", "finalize-success", "finalize-error"}:
+                             "prepare", "prepare-after", "filtered", "post",
+                             "post-after", "finalize", "finalize-success",
+                             "finalize-error"}:
                 format_string = value
                 event = ("prepare",)