Move video url extraction logic to crawler

PFERD/ilias/crawler.py

@@ -3,6 +3,7 @@ Contains an ILIAS crawler alongside helper functions.
 """
 
 import datetime
+import json
 import logging
 import re
 from enum import Enum
@@ -380,22 +381,44 @@ class IliasCrawler:
 
         video_path: Path = Path(parent_path, title)
 
+        video_url = self._abs_url_from_link(link)
+
         # The video had a direct download button we can use instead
         if direct_download:
             LOGGER.debug("Using direct download for video %r", str(video_path))
-            return [IliasDownloadInfo(
-                video_path,
-                self._abs_url_from_link(link),
-                modification_time
-            )]
+            return [IliasDownloadInfo(video_path, video_url, modification_time)]
 
         return [IliasDownloadInfo(
             video_path,
-            self._abs_url_from_link(link),
-            modification_time,
-            unpack_video=True
+            self._crawl_video_url_from_play_link(video_url),
+            modification_time
         )]
 
+    def _crawl_video_url_from_play_link(self, play_url: str) -> Callable[[], Optional[str]]:
+        def inner() -> Optional[str]:
+            # Fetch the actual video page. This is a small wrapper page initializing a javscript
+            # player. Sadly we can not execute that JS. The actual video stream url is nowhere
+            # on the page, but defined in a JS object inside a script tag, passed to the player
+            # library.
+            # We do the impossible and RegEx the stream JSON object out of the page's HTML source
+            video_page_soup = soupify(self._session.get(play_url))
+            regex: re.Pattern = re.compile(
+                r"({\"streams\"[\s\S]+?),\s*{\"paella_config_file", re.IGNORECASE
+            )
+            json_match = regex.search(str(video_page_soup))
+
+            if json_match is None:
+                PRETTY.warning(f"Could not find json stream info for {play_url!r}")
+                return None
+            json_str = json_match.group(1)
+
+            # parse it
+            json_object = json.loads(json_str)
+            # and fetch the video url!
+            video_url = json_object["streams"][0]["sources"]["mp4"][0]["src"]
+            return video_url
+        return inner
+
     def _crawl_exercises(self, element_path: Path, url: str) -> List[IliasDownloadInfo]:
         """
         Crawl files offered for download in exercises.