feat: add prometheus metrics

src/events/client/onReady.ts

@@ -3,6 +3,7 @@ import { scheduleJob } from "node-schedule";
 import { ExtendedClient } from "../../interfaces/ExtendedClient";
 import { maintainSecurity } from "../../modules/maintainSecurity";
 import { postBirthdays } from "../../modules/postBirthdays";
+import { Prometheus } from "../../modules/prometheus";
 import { registerCommands } from "../../utils/registerCommands";
 import { sendDebugMessage } from "../../utils/sendDebugMessage";
 
@@ -14,6 +15,7 @@ import { sendDebugMessage } from "../../utils/sendDebugMessage";
 export const onReady = async (bot: ExtendedClient) => {
   await sendDebugMessage(bot, `Logged in as ${bot.user?.tag}`);
   await registerCommands(bot);
+  bot.analytics = new Prometheus(bot);
 
   // Daily at 9am PST
   scheduleJob("birthdays", "0 9 * * *", async () => await postBirthdays(bot));

src/events/guild/onGuildCreate.ts

@@ -15,4 +15,5 @@ export const onGuildCreate = async function (
   await bot.env.debugHook.send({
     content: `JOINED GUILD: ${guild.name} (${guild.id}) - owned by ${owner?.displayName} (${owner.id})`
   });
+  bot.analytics.updateGuilds(bot);
 };

src/events/guild/onGuildDelete.ts

@@ -36,6 +36,7 @@ export const onGuildDelete = async function (
     await bot.db.security
       .deleteMany({ where: { serverId: guild.id } })
       .catch(() => null);
+    bot.analytics.updateGuilds(bot);
   } catch (err) {
     await errorHandler(bot, "on guild delete", err);
   }

src/events/interaction/onInteraction.ts

@@ -35,6 +35,7 @@ export const onInteraction = async (
       );
       return;
     }
+    bot.analytics.commandUsed();
     if (interaction.isChatInputCommand()) {
       handleChatInputCommand(bot, interaction);
     }

src/interfaces/ExtendedClient.ts

@@ -4,6 +4,8 @@ import { Client, WebhookClient } from "discord.js";
 import { Command } from "./Command";
 import { Context } from "./Context";
 
+import type { Prometheus } from "../modules/prometheus.js";
+
 export interface ExtendedClient extends Client {
   env: {
     token: string;
@@ -12,6 +14,7 @@ export interface ExtendedClient extends Client {
     devMode: boolean;
   };
   db: PrismaClient;
+  analytics: Prometheus;
   commands: Command[];
   contexts: Context[];
   configs: { [serverId: string]: Omit<configs, "id"> };

src/modules/prometheus.ts

@@ -0,0 +1,29 @@
+import client, { Counter, Gauge } from "prom-client";
+import type { ExtendedClient } from "../interfaces/ExtendedClient.js";
+
+export class Prometheus {
+  private client = client;
+  private guilds: Gauge;
+  private commands: Counter;
+
+  constructor(bot: ExtendedClient) {
+    this.guilds = new Gauge({
+      name: "guilds",
+      help: "The number of guilds the bot is in."
+    });
+    this.guilds.set(bot.guilds.cache.size);
+    this.commands = new Counter({
+      name: "commands",
+      help: "The number of commands that have been used since last boot."
+    });
+    this.client.collectDefaultMetrics();
+  }
+
+  public commandUsed() {
+    this.commands.inc();
+  }
+
+  public updateGuilds(bot: ExtendedClient) {
+    this.guilds.set(bot.guilds.cache.size);
+  }
+}

src/server/serve.ts

@@ -6,6 +6,7 @@ import https from "https";
 import { Octokit } from "@octokit/rest";
 import { GuildTextBasedChannel } from "discord.js";
 import express from "express";
+import { register } from "prom-client";
 
 import { IgnoredActors, ThankYou } from "../config/Github";
 import { ExtendedClient } from "../interfaces/ExtendedClient";
@@ -47,6 +48,15 @@ export const serve = async (bot: ExtendedClient) => {
     res.send("bot online!");
   });
 
+  app.get("/metrics", async (_req, res) => {
+    try {
+      res.set("Content-Type", register.contentType);
+      res.end(await register.metrics());
+    } catch (err) {
+      res.status(500).end(err);
+    }
+  });
+
   app.post("/kofi", async (req, res) => {
     const payload = JSON.parse(req.body.data);
     const {