[gelbooru] detect returned favorites order (#5220)

gallery_dl/extractor/gelbooru.py

@@ -32,6 +32,9 @@ class GelbooruBase():
         url = self.root + "/index.php?page=dapi&q=index&json=1"
         data = self.request(url, params=params).json()
 
+        if not key:
+            return data
+
         try:
             posts = data[key]
         except KeyError:
@@ -167,13 +170,54 @@ class GelbooruFavoriteExtractor(GelbooruBase,
         params = {
             "s"    : "favorite",
             "id"   : self.favorite_id,
-            "limit": "1",
+            "limit": "2",
         }
 
-        count = self._api_request(params, "@attributes", True)[0]["count"]
+        data = self._api_request(params, None, True)
+
+        count = data["@attributes"]["count"]
         if count <= self.offset:
+            return ()
+
+        favs = data["favorite"]
+        try:
+            order = 1 if favs[0]["id"] < favs[1]["id"] else -1
+        except LookupError:
+            order = 0
+
+        if order > 0:
+            self.log.debug("API yields favorites in ascending order")
+            self.log.debug("Returning them in reverse")
+            return self._pagination_reverse(params, count)
+
+        self.log.debug("API yields favorites in descending order")
+        return self._pagination(params, count)
+
+    def _pagination(self, params, count):
+        if self.offset:
+            pnum, skip = divmod(self.offset, self.per_page)
+        else:
+            pnum = skip = 0
+
+        params["pid"] = pnum
+        params["limit"] = self.per_page
+
+        while True:
+            favs = self._api_request(params, "favorite", True)
+
+            if not favs:
                 return
 
+            if skip:
+                favs = favs[skip:]
+                skip = 0
+
+            for fav in favs:
+                yield from self._api_request({"id": fav["favorite"]})
+
+            params["pid"] += 1
+
+    def _pagination_reverse(self, params, count):
         pnum, last = divmod(count-1, self.per_page)
         if self.offset > last:
             # page number change
@@ -182,7 +226,6 @@ class GelbooruFavoriteExtractor(GelbooruBase,
             pnum -= diff + 1
         skip = self.offset
 
-        # paginate over them in reverse
         params["pid"] = pnum
         params["limit"] = self.per_page