Merge pull request #2078 from python-discord/chris/fix/help-channel-errors

Ensure claimant cache is populated on help channel init

2 files changed, 62 insertions, 7 deletions

diff --git a/bot/exts/help_channels/_channel.py b/bot/exts/help_channels/_channel.py
index e43c1e789..ff9e6a347 100644
--- a/bot/exts/help_channels/_channel.py
+++ b/bot/exts/help_channels/_channel.py
@@ -1,3 +1,4 @@
+import re
 import typing as t
 from datetime import timedelta
 from enum import Enum
@@ -16,6 +17,7 @@ log = get_logger(__name__)
 
 MAX_CHANNELS_PER_CATEGORY = 50
 EXCLUDED_CHANNELS = (constants.Channels.cooldown,)
+CLAIMED_BY_RE = re.compile(r"Channel claimed by <@!?(?P<user_id>\d{17,20})>\.$")
 
 
 class ClosingReason(Enum):
@@ -157,3 +159,35 @@ async def move_to_bottom(channel: discord.TextChannel, category_id: int, **optio
     # Now that the channel is moved, we can edit the other attributes
     if options:
         await channel.edit(**options)
+
+
+async def ensure_cached_claimant(channel: discord.TextChannel) -> None:
+    """
+    Ensure there is a claimant cached for each help channel.
+
+    Check the redis cache first, return early if there is already a claimant cached.
+    If there isn't an entry in redis, search for the "Claimed by X." embed in channel history.
+        Stopping early if we discover a dormant message first.
+
+    If a claimant could not be found, send a warning to #helpers and set the claimant to the bot.
+    """
+    if await _caches.claimants.get(channel.id):
+        return
+
+    async for message in channel.history(limit=1000):
+        if message.author.id != bot.instance.user.id:
+            # We only care about bot messages
+            continue
+        if message.embeds:
+            if _message._match_bot_embed(message, _message.DORMANT_MSG):
+                log.info("Hit the dormant message embed before finding a claimant in %s (%d).", channel, channel.id)
+                break
+            user_id = CLAIMED_BY_RE.match(message.embeds[0].description).group("user_id")
+            await _caches.claimants.set(channel.id, int(user_id))
+            return
+
+    await bot.instance.get_channel(constants.Channels.helpers).send(
+        f"I couldn't find a claimant for {channel.mention} in that last 1000 messages. "
+        "Please use your helper powers to close the channel if/when appropriate."
+    )
+    await _caches.claimants.set(channel.id, bot.instance.user.id)
diff --git a/bot/exts/help_channels/_cog.py b/bot/exts/help_channels/_cog.py
index 541c791e5..f276a7993 100644
--- a/bot/exts/help_channels/_cog.py
+++ b/bot/exts/help_channels/_cog.py
@@ -111,14 +111,31 @@ class HelpChannels(commands.Cog):
         """
         log.info(f"Channel #{message.channel} was claimed by `{message.author.id}`.")
 
+        try:
+            await self.move_to_in_use(message.channel)
+        except discord.DiscordServerError:
+            try:
+                await message.channel.send(
+                    "The bot encountered a Discord API error while trying to move this channel, please try again later."
+                )
+            except Exception as e:
+                log.warning("Error occurred while sending fail claim message:", exc_info=e)
+            log.info(
+                "500 error from Discord when moving #%s (%d) to in-use for %s (%d). Cancelling claim.",
+                message.channel.name,
+                message.channel.id,
+                message.author.name,
+                message.author.id,
+            )
+            self.bot.stats.incr("help.failed_claims.500_on_move")
+            return
+
         embed = discord.Embed(
             description=f"Channel claimed by {message.author.mention}.",
             color=constants.Colours.bright_green,
         )
         await message.channel.send(embed=embed)
 
-        await self.move_to_in_use(message.channel)
-
         # Handle odd edge case of `message.author` not being a `discord.Member` (see bot#1839)
         if not isinstance(message.author, discord.Member):
             log.debug(f"{message.author} ({message.author.id}) isn't a member. Not giving cooldown role or sending DM.")
@@ -309,6 +326,7 @@ class HelpChannels(commands.Cog):
 
         log.trace("Moving or rescheduling in-use channels.")
         for channel in _channel.get_category_channels(self.in_use_category):
+            await _channel.ensure_cached_claimant(channel)
             await self.move_idle_channel(channel, has_task=False)
 
         # Prevent the command from being used until ready.
@@ -434,18 +452,21 @@ class HelpChannels(commands.Cog):
     async def _unclaim_channel(
         self,
         channel: discord.TextChannel,
-        claimant_id: int,
+        claimant_id: t.Optional[int],
         closed_on: _channel.ClosingReason
     ) -> None:
         """Actual implementation of `unclaim_channel`. See that for full documentation."""
         await _caches.claimants.delete(channel.id)
         await _caches.session_participants.delete(channel.id)
 
-        claimant = await members.get_or_fetch_member(self.guild, claimant_id)
-        if claimant is None:
-            log.info(f"{claimant_id} left the guild during their help session; the cooldown role won't be removed")
+        if not claimant_id:
+            log.info("No claimant given when un-claiming %s (%d). Skipping role removal.", channel, channel.id)
         else:
-            await members.handle_role_change(claimant, claimant.remove_roles, self.cooldown_role)
+            claimant = await members.get_or_fetch_member(self.guild, claimant_id)
+            if claimant is None:
+                log.info(f"{claimant_id} left the guild during their help session; the cooldown role won't be removed")
+            else:
+                await members.handle_role_change(claimant, claimant.remove_roles, self.cooldown_role)
 
         await _message.unpin(channel)
         await _stats.report_complete_session(channel.id, closed_on)