Improve the spam detection (#7)

If a user sends a message to three channels in a 5 minute window containing a link or attachment they will be banned.
These requirements are a bit loose but we can deal with any false positives manually. I don't think there will be many, if any.
The latest spam examples only have image attachments and the images are slightly different so there is no easy way to detect this.

Author: gentlegiantJGC

amulet_discord_bot/bot.py

@@ -4,6 +4,7 @@
 import gzip
 import os
 from difflib import SequenceMatcher
+from datetime import datetime, timedelta, timezone
 
 import discord
 
@@ -184,33 +185,36 @@ async def _process_message(self, message: discord.Message) -> None:
             await self._log(msg)
             return
 
-        if (
-            amulet_server is not None
-            and self.has_link(message_text)
-            and not self.has_github_link(message_text)
+        if amulet_server is not None and (
+            self.has_link(message_text) or message.attachments
         ):
-            # remove spam messages
-            count = 1
-            for channel in amulet_server.text_channels:
-                if (
-                    channel.id != channel_id
-                    and channel.permissions_for(author).read_message_history
-                ):
-                    async for other_message in channel.history(limit=30):
-                        other_author = other_message.author
-                        if (
-                            other_author.id == author_id
-                            and SequenceMatcher(
-                                None, message_text, other_message.content
-                            ).ratio()
-                            > 0.9
+
+            async def is_spam() -> bool:
+                count = 1
+                for channel in amulet_server.text_channels:
+                    if (
+                        channel.id != channel_id
+                        and channel.permissions_for(author).read_message_history
+                    ):
+                        async for other_message in channel.history(
+                            limit=30,
+                            after=datetime.now(timezone.utc) - timedelta(minutes=5),
                         ):
-                            count += 1
-                            break
-                if count >= 3:
-                    break
-            if count >= 3:
-                await self.ban(author, f"spamming\n{message_text}")
+                            if other_message.author.id == author_id and (
+                                self.has_link(other_message.content)
+                                or other_message.attachments
+                            ):
+                                count += 1
+                                break
+                        if count >= 3:
+                            return True
+                return False
+
+            if await is_spam():
+                reason = f"spamming\nSTART MESSAGE\n{message_text}\nEND MESSAGE"
+                for attachment in message.attachments:
+                    reason += f"\n{attachment.url}"
+                await self.ban(author, reason)
             return
 
     async def on_message(self, message: discord.Message) -> None: