Centralize periodic checks for mutes, tempbans, vcalerts, reminders, and scheduled posts

This should result in a significant performance improvement.
The new method is also more precise than the old one, allowing
the aforementioned checks to be performed with second-precision.

backend/src/data/loops/expiringMutesLoop.ts

@@ -0,0 +1,72 @@
+import { lazyMemoize, memoize, MINUTES } from "../../utils";
+import { Mutes } from "../Mutes";
+import Timeout = NodeJS.Timeout;
+import moment from "moment-timezone";
+import { Mute } from "../entities/Mute";
+import { emitGuildEvent, hasGuildEventListener } from "../GuildEvents";
+
+const LOOP_INTERVAL = 15 * MINUTES;
+const MAX_TRIES_PER_SERVER = 3;
+const getMutesRepository = lazyMemoize(() => new Mutes());
+const timeouts = new Map<string, Timeout>();
+
+function muteToKey(mute: Mute) {
+  return `${mute.guild_id}/${mute.user_id}`;
+}
+
+function broadcastExpiredMute(mute: Mute, tries = 0) {
+  console.log(`[EXPIRING MUTES LOOP] Broadcasting expired mute: ${mute.guild_id}/${mute.user_id}`);
+  if (!hasGuildEventListener(mute.guild_id, "expiredMute")) {
+    // If there are no listeners registered for the server yet, try again in a bit
+    if (tries < MAX_TRIES_PER_SERVER) {
+      timeouts.set(
+        muteToKey(mute),
+        setTimeout(() => broadcastExpiredMute(mute, tries + 1), 1 * MINUTES),
+      );
+    }
+    return;
+  }
+  emitGuildEvent(mute.guild_id, "expiredMute", [mute]);
+}
+
+export async function runExpiringMutesLoop() {
+  console.log("[EXPIRING MUTES LOOP] Clearing old timeouts");
+  for (const timeout of timeouts.values()) {
+    clearTimeout(timeout);
+  }
+
+  console.log("[EXPIRING MUTES LOOP] Setting timeouts for expiring mutes");
+  const expiringMutes = await getMutesRepository().getSoonExpiringMutes(LOOP_INTERVAL);
+  for (const mute of expiringMutes) {
+    const remaining = Math.max(0, moment.utc(mute.expires_at!).diff(moment.utc()));
+    timeouts.set(
+      muteToKey(mute),
+      setTimeout(() => broadcastExpiredMute(mute), remaining),
+    );
+  }
+
+  console.log("[EXPIRING MUTES LOOP] Scheduling next loop");
+  setTimeout(() => runExpiringMutesLoop(), LOOP_INTERVAL);
+}
+
+export function registerExpiringMute(mute: Mute) {
+  clearExpiringMute(mute);
+
+  console.log("[EXPIRING MUTES LOOP] Registering new expiring mute");
+  const remaining = Math.max(0, moment.utc(mute.expires_at!).diff(moment.utc()));
+  if (remaining > LOOP_INTERVAL) {
+    return;
+  }
+
+  timeouts.set(
+    muteToKey(mute),
+    setTimeout(() => broadcastExpiredMute(mute), remaining),
+  );
+}
+
+export function clearExpiringMute(mute: Mute) {
+  console.log("[EXPIRING MUTES LOOP] Clearing expiring mute");
+  if (timeouts.has(muteToKey(mute))) {
+    clearTimeout(timeouts.get(muteToKey(mute))!);
+  }
+}