add automatic help message

nomen/main.py

@@ -1,3 +1,4 @@
+import datetime
 import io
 import logging
 import os
@@ -7,6 +8,7 @@ import textwrap
 import traceback
 from contextlib import redirect_stdout
 
+import disnake
 from disnake import Embed, Guild, Intents, Message, Thread
 from disnake.ext import commands
 from disnake.ext.commands import Bot, Paginator
@@ -189,6 +191,51 @@ async def on_error(event, *args, **kwargs):
     log.error(f"Error in event {event}.\nargs={pargs}\nkwargs={pkwargs}", exc_info=sys.exc_info())
 
 
+help_timeouts = {}
+
+
+@bot.listen()
+async def on_message(message: Message):
+    if message.author == bot.user:
+        return
+
+    ctx = await bot.get_context(message)
+    if ctx.valid:
+        return
+
+    now = disnake.utils.utcnow()
+    if timeout := help_timeouts.get(ctx.channel.id, None):
+        if now < timeout:
+            return
+
+    c = message.content.lower()
+    prefix = await bot.get_guild_prefix(ctx.guild) or "@nomen "
+
+    if "help" in c and "nomen" in c:
+        help_timeouts[ctx.channel.id] = now + datetime.timedelta(minutes=5)
+        await message.reply(f"""\
+Heya!
+
+- To add a keyword, use the command `{prefix}keyword add <words here>`
+  (`{prefix}keyword` can be shortened to `{prefix}kw`)
+- To remove a keyword, use `{prefix}keyword remove <keyword>`
+- To view all of your keywords, use `{prefix}keyword list`
+- To ignore a person/channel/category, use `{prefix}keyword ignore <target>`
+  To unignore, `{prefix}keyword unignore <target>`
+- To block a person across all servers, `{prefix}keyword block <target>`
+  To unblock, `{prefix}keyword unblock <target>`
+- To pause/unpause notifications in a server, use `{prefix}keyword pause`/`{prefix}keyword unpause`
+
+For other commands, see `{prefix}help`. Use `{prefix}help <command>` for detailed help.
+
+If you are familiar with the Dusty bot (almost) all commands for Dusty work with Nomen, just replace `>` with `{prefix}`.
+If you already have keywords in Dusty, you can import them into Nomen easily by:
+1. Use `>notif list` to get your list of keywords from Dusty
+2. Copy the list (**without the header/title**)
+3. Run `{prefix}nomen import <paste list here>`
+        """)
+
+
 @bot.command(hidden=True)
 @commands.is_owner()
 async def echo(ctx, arg):