feat: add prometheus metrics

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);
+  }
+}