Add arg parsing and subcommands

* pull - will download thumbnails and update the database
* serve - (in the future) will run an HTTP frontend server to display
  the pulled data

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

chanbans/__main__.py

@@ -1,6 +1,46 @@
 import asyncio
+import argparse
 
 from .pull import pull
 
 
-asyncio.run(pull())
+def parse_args():
+    parser = argparse.ArgumentParser(description="Run 4chan bans archiver")
+    subparsers = parser.add_subparsers(title="Commands", dest="command")
+
+    subcommands = set()
+
+    def add_subcommand(subcommand: str, *args, **kwargs):
+        nonlocal subparsers, subcommands
+        assert (
+            subcommand not in subcommands
+        ), f"subcommand {subcommand} was already registered"
+        subcommands |= {subcommand}
+        return subparsers.add_parser(subcommand, *args, **kwargs)
+
+    _pull_parser = add_subcommand(
+        "pull",
+        help="Pull bans from 4chan, save thumbnails, update the database, and exit",
+    )
+    _serve_parser = add_subcommand("serve", help="Start HTTP server")
+    _help_parser = add_subcommand("help", help="Show this help message")
+
+    args = parser.parse_args()
+
+    if args.command not in subcommands or args.command == "help":
+        parser.print_help()
+
+    return args
+
+
+async def main():
+    args = parse_args()
+    match args.command:
+        case "pull":
+            await pull()
+        case "serve":
+            print("TODO: HTTP server")
+        case command:
+            assert False, f"unknown command {command} that was not caught in add_subcommand"
+
+asyncio.run(main())

chanbans/pull.py

@@ -12,7 +12,11 @@ from .files import file_cache
 
 BANS_URL = "https://4chan.org/bans"
 PREVIEW_RE = re.compile(r"var postPreviews = (.+)")
+# TODO(args) --thumbs-dir arg
 THUMBS_DIR = Path("thumbs")
+# TODO(args) --cache-dir arg
+# this is kind of hard to do because it's set in a decorator. I think the best option would be to
+# make a global "config" object
 CACHE_DIR = Path("bans")