Verification: implement unverified role ping task

We're making good use of d.py's tasks framework. RedisCache is used to
persist the reminder message ids, which can conveniently be converted
into timestamps.

It is therefore trivial to determine the time to sleep before the first
ping. After that, the bot simply pings every n hours.

1 files changed, 52 insertions, 0 deletions

diff --git a/bot/cogs/verification.py b/bot/cogs/verification.py
index ca7631db2..42088896d 100644
--- a/bot/cogs/verification.py
+++ b/bot/cogs/verification.py
@@ -7,6 +7,7 @@ from datetime import datetime, timedelta
 import discord
 from discord.ext import tasks
 from discord.ext.commands import Cog, Context, command
+from discord.utils import snowflake_time
 
 from bot import constants
 from bot.bot import Bot
@@ -283,6 +284,57 @@ class Verification(Cog):
         )
 
     # endregion
+    # region: periodically ping @Unverified
+
+    @tasks.loop(hours=REMINDER_FREQUENCY)
+    async def ping_unverified(self) -> None:
+        """
+        Delete latest `REMINDER_MESSAGE` and send it again.
+
+        This utilizes RedisCache to persist the latest reminder message id.
+        """
+        await self.bot.wait_until_guild_available()
+        verification = self.bot.get_guild(constants.Guild.id).get_channel(constants.Channels.verification)
+
+        last_reminder: t.Optional[int] = await self.reminder_cache.get("last_reminder")
+
+        if last_reminder is not None:
+            log.trace(f"Found verification reminder message in cache, deleting: {last_reminder}")
+
+            with suppress(discord.HTTPException):  # If something goes wrong, just ignore it
+                await self.bot.http.delete_message(verification.id, last_reminder)
+
+        log.trace("Sending verification reminder")
+        new_reminder = await verification.send(REMINDER_MESSAGE)
+
+        await self.reminder_cache.set("last_reminder", new_reminder.id)
+
+    @ping_unverified.before_loop
+    async def _before_first_ping(self) -> None:
+        """
+        Sleep until `REMINDER_MESSAGE` should be sent again.
+
+        If latest reminder is not cached, exit instantly. Otherwise, wait wait until the
+        configured `REMINDER_FREQUENCY` has passed.
+        """
+        last_reminder: t.Optional[int] = await self.reminder_cache.get("last_reminder")
+
+        if last_reminder is None:
+            log.trace("Latest verification reminder message not cached, task will not wait")
+            return
+
+        # Convert cached message id into a timestamp
+        time_since = datetime.utcnow() - snowflake_time(last_reminder)
+        log.trace(f"Time since latest verification reminder: {time_since}")
+
+        to_sleep = timedelta(hours=REMINDER_FREQUENCY) - time_since
+        log.trace(f"Time to sleep until next ping: {to_sleep}")
+
+        # Delta can be negative if `REMINDER_FREQUENCY` has already passed
+        secs = max(to_sleep.total_seconds(), 0)
+        await asyncio.sleep(secs)
+
+    # endregion
     # region: listeners
 
     @Cog.listener()