Adds a comic format registry

There is the limitation that you still need to manually import all modules that register a new comic format, but this does give us a lot of flexibility

__main__.py

@@ -5,19 +5,22 @@ import argparse
 import datetime
 import threading
 import time
+from urllib.parse import urlparse
 from pathlib import Path
-from comic_download.xkcd import XKCDComic, XKCDComicStrip
+from comic_download import Comic, find_comic_class
+import comic_download.xkcd
 
 def setup_args():
     parser = argparse.ArgumentParser(
                     prog='xkcd',
                     description='Downloads the entire XKCD collection')
 
+    parser.add_argument('url', action='extend', nargs='+', type=urlparse, help="The URLs to load")
     parser.add_argument('-o', '--output', type=Path, default=Path(), help="The directory to dump the files to.")
     parser.add_argument('-w', '--wait', type=int, default=0, help="How many seconds to wait between each request")
     parser.add_argument('-t', '--threads', type=int, default=10, help="How many download threads will run at once")
-    parser.add_argument('-s', '--start', type=int, default=0, help="The comic index to start at. A zero will be interpreted as using up to the first comic.")
-    parser.add_argument('-e', '--end', type=int, default=0, help="The comic index to end at. A zero will be interpreted as using up to the last comic.")
+    parser.add_argument('-s', '--start', type=int, default=0, help="The comic index to start at. A zero will be interpreted as using up to the first comic. This option is only valid if there is a single URL.")
+    parser.add_argument('-e', '--end', type=int, default=0, help="The comic index to end at. A zero will be interpreted as using up to the last comic. This option is only valid if there is a single URL.")
     parser.add_argument('-l', '--latest', action='store_true', help="If set, only the latest comic will be downloaded")
     parser.add_argument('-p', '--plain', action='store_true', help="If set, only the raw image will be downloaded, and titles, caption, etc. will not be added.")
     
@@ -40,7 +43,7 @@ def setup_logging():
     ch.doRollover()
     logger.addHandler(ch)
 
-def load_strip(base_path, index, plain, thread_limit):
+def load_strip(base_path, comic, identifier, plain, thread_limit):
     """
     Threading function for downloading XKCD strips.
     
@@ -48,7 +51,7 @@ def load_strip(base_path, index, plain, thread_limit):
     
     """
     with thread_limit:
-        strip = XKCDComicStrip(index)
+        strip = comic.create_strip(identifier)
         strip.await_load()
         if not strip.get_package_path(base_path).exists():
             strip.await_download()
@@ -65,23 +68,27 @@ if __name__ == "__main__":
         base_path.mkdir(parents=True)
 
     logging.info("Beginning parsing")
-    comic = XKCDComic()
-    comic.await_load()
-    logging.info("There are %d comics", comic.latest_identifier)
-    if args.latest:
-        r = range(comic.latest_identifier, comic.latest_identifier + 1)
-    else:
-        start = args.start or 1
-        end = args.end or comic.latest_identifier
-        r = range(end, start - 1, -1)
-
+        
     threads = []
     thread_limit = threading.BoundedSemaphore(value=args.threads)
     
-    for index in r:
-        t = threading.Thread(name=str(index), target=load_strip, args=(base_path, index, args.plain, thread_limit))
-        threads.append(t)
-        t.start()
+    for url in args.url:
+        comic_type = find_comic_class(url.netloc + url.path)
+        comic = comic_type.create_from_url(url)
+        comic.await_load()
+        logging.info("There are %d comics", comic.latest_identifier)
+        if args.latest:
+            r = [comic.get_latest_strip()]
+        else:
+            r = comic.get_all_strips()
+            start = args.start or 0
+            end = args.end or (len(r) - 1)
+            r = r[start:end + 1]
+    
+        for index in reversed(r):
+            t = threading.Thread(name=str(comic) + str(index), target=load_strip, args=(base_path, comic, index, args.plain, thread_limit))
+            threads.append(t)
+            t.start()
 
     for t in threads:
         t.join()