implement (sub)category-transfer between extractors (#41)

ImageFap- and all Manga-Extractors will transfer their (sub)category
values to other extractors instantiated by them, which will in turn
allow those to use options set for their parents.

Example:
ImagefapGalleryExtractors will use options set under
extractor.imagefap.user, if (and only if) they have been instantiated by
a ImagefapUserExtractor; and options from extractor.imagefap.gallery
otherwise.

gallery_dl/extractor/common.py

@@ -25,6 +25,7 @@ class Extractor():
 
     category = ""
     subcategory = ""
+    categorytransfer = False
     directory_fmt = ["{category}"]
     filename_fmt = "{filename}"
     cookiedomain = ""
@@ -147,6 +148,7 @@ class AsynchronousExtractor(Extractor):
 class MangaExtractor(Extractor):
 
     subcategory = "manga"
+    categorytransfer = True
     scheme = "http"
     root = ""
     reverse = True

gallery_dl/extractor/imagefap.py

@@ -136,8 +136,7 @@ class ImagefapUserExtractor(Extractor):
     """Extractor for all galleries from a user at imagefap.com"""
     category = "imagefap"
     subcategory = "user"
-    directory_fmt = ["{category}", "{gallery_id} {title}"]
+    categorytransfer = True
-    filename_fmt = "{category}_{gallery_id}_{name}.{extension}"
     pattern = [(r"(?:https?://)?(?:www\.)?imagefap\.com/"
                 r"profile(?:\.php\?user=|/)([^/]+)"),
                (r"(?:https?://)?(?:www\.)?imagefap\.com/"

gallery_dl/job.py

@@ -121,6 +121,12 @@ class Job():
         kwdict["category"] = self.extractor.category
         kwdict["subcategory"] = self.extractor.subcategory
 
+    def _prepare(self, job):
+        if self.extractor.categorytransfer:
+            job.extractor.category = self.extractor.category
+            job.extractor.subcategory = self.extractor.subcategory
+        return job
+
     def _write_unsupported(self, url):
         if self.ufile:
             print(url, file=self.ufile, flush=True)
@@ -150,7 +156,7 @@ class DownloadJob(Job):
 
     def handle_queue(self, url, keywords):
         try:
-            DownloadJob(url).run()
+            self._prepare(DownloadJob(url)).run()
         except exception.NoExtractorError:
             self._write_unsupported(url)
 
@@ -183,9 +189,18 @@ class KeywordJob(Job):
         self.print_keywords(keywords)
 
     def handle_queue(self, url, keywords):
-        print("Keywords for chapter filters:")
+        if not keywords:
-        print("-----------------------------")
+            self.extractor.log.info(
-        self.print_keywords(keywords)
+                "This extractor transfers work to other extractors "
+                "and does not provide any keywords on its own. Try "
+                "'gallery-dl -K \"%s\"' instead.", url)
+        else:
+            print("Keywords for --chapter-filter:")
+            print("------------------------------")
+            self.print_keywords(keywords)
+            if self.extractor.categorytransfer:
+                print()
+                self._prepare(KeywordJob(url)).run()
         raise exception.StopExtraction()
 
     @staticmethod
@@ -227,7 +242,7 @@ class UrlJob(Job):
 
     def handle_queue(self, url, _):
         try:
-            UrlJob(url, self.depth + 1).run()
+            self._prepare(UrlJob(url, self.depth + 1)).run()
         except exception.NoExtractorError:
             self._write_unsupported(url)