Add the `metrics` cog.

2 files changed, 41 insertions, 0 deletions

diff --git a/bot/__main__.py b/bot/__main__.py
index 84bc7094b..61271a692 100644
--- a/bot/__main__.py
+++ b/bot/__main__.py
@@ -40,6 +40,7 @@ bot.load_extension("bot.cogs.duck_pond")
 bot.load_extension("bot.cogs.free")
 bot.load_extension("bot.cogs.information")
 bot.load_extension("bot.cogs.jams")
+bot.load_extension("bot.cogs.metrics")
 bot.load_extension("bot.cogs.moderation")
 bot.load_extension("bot.cogs.off_topic_names")
 bot.load_extension("bot.cogs.reddit")
diff --git a/bot/cogs/metrics.py b/bot/cogs/metrics.py
new file mode 100644
index 000000000..79c754c21
--- /dev/null
+++ b/bot/cogs/metrics.py
@@ -0,0 +1,40 @@
+from collections import defaultdict
+
+from discord import Status
+from discord.ext.commands import Cog
+from prometheus_client import Gauge
+
+from bot.bot import Bot
+
+
+class Metrics(Cog):
+    """Exports metrics for Prometheus."""
+
+    PREFIX = 'pydis_bot_'
+
+    def __init__(self, bot: Bot) -> None:
+        self.bot = bot
+
+        self.guild_members = Gauge(
+            name=f'{self.PREFIX}server_members',
+            documentation="Total members by status.",
+            labelnames=('guild_id', 'status')
+        )
+
+    @Cog.listener()
+    async def on_ready(self) -> None:
+        members_by_status = defaultdict(lambda: defaultdict(int))
+
+        await self.bot.request_offline_members(*self.bot.guilds)
+        for guild in self.bot.guilds:
+            for member in guild.members:
+                members_by_status[guild.id][member.status] += 1
+
+        for guild_id, members in members_by_status.items():
+            for status, count in members.items():
+                self.guild_members.labels(guild_id=guild_id, status=str(status)).set(count)
+
+
+def setup(bot: Bot) -> None:
+    """Load the Metrics cog."""
+    bot.add_cog(Metrics(bot))