don't double-post images sent using pluralkit

data_expunged.py

@@ -20,21 +20,38 @@ async def on_message(message):
         and message.attachments
         and not any(a.is_spoiler() for a in message.attachments)):
 
-        attachments = []
-        try:
-            for a in message.attachments:
-                f = await a.to_file()
-                f.filename = 'SPOILER_' + f.filename
-                attachments.append(f)
-        except discord.DiscordException as e:
-            print('error reading attachments: {0}'.format(e), file=sys.stderr)
-            return
+        pluralkit = False
+        if message.webhook_id is not None:
+            try:
+                webhook = await client.fetch_webhook(message.webhook_id)
+            except discord.Forbidden as e:
+                print('error fetching message webhook: {0}'.format(e), file=sys.stderr)
+                await message.channel.send("I can't inspect the webhook on this message because I don't have the permissions I need. This is important so I can interact properly with messages sent by PluralKit. Admins, please make sure I have the Manage Webhooks permission in all channels where people want to use me.")
+                return
+            except discord.DiscordException as e:
+                print('error fetching message webhook: {0}'.format(e), file=sys.stderr)
+                return
+            if webhook.user is not None and webhook.user.name == "PluralKit":
+                pluralkit = True
 
-        try:
-            await message.channel.send("{0} says: {1}".format(message.author.mention, message.content), files=attachments)
-        except discord.DiscordException as e:
-            print('error sending message: {0}'.format(e), file=sys.stderr)
-            return
+        # If this is a message that's being reposted by PluralKit,
+        # assume we already caught and reposted the original, and
+        # just delete this one without reposting a spoilered version
+        if not pluralkit:
+            attachments = []
+            try:
+                for a in message.attachments:
+                    f = await a.to_file()
+                    f.filename = 'SPOILER_' + f.filename
+                    attachments.append(f)
+            except discord.DiscordException as e:
+                print('error reading attachments: {0}'.format(e), file=sys.stderr)
+                return
+            try:
+                await message.channel.send("{0} says: {1}".format(message.author.mention, message.content), files=attachments)
+            except discord.DiscordException as e:
+                print('error sending message: {0}'.format(e), file=sys.stderr)
+                return
 
         try:
             await message.delete()