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/expiringVCAlertsLoop.ts

@@ -0,0 +1,68 @@
+import { lazyMemoize, MINUTES } from "../../utils";
+import moment from "moment-timezone";
+import { emitGuildEvent, hasGuildEventListener } from "../GuildEvents";
+import Timeout = NodeJS.Timeout;
+import { VCAlerts } from "../VCAlerts";
+import { VCAlert } from "../entities/VCAlert";
+
+const LOOP_INTERVAL = 15 * MINUTES;
+const MAX_TRIES_PER_SERVER = 3;
+const getVCAlertsRepository = lazyMemoize(() => new VCAlerts());
+const timeouts = new Map<number, Timeout>();
+
+function broadcastExpiredVCAlert(alert: VCAlert, tries = 0) {
+  console.log(`[EXPIRING VCALERTS LOOP] Broadcasting expired vcalert: ${alert.guild_id}/${alert.user_id}`);
+  if (!hasGuildEventListener(alert.guild_id, "expiredVCAlert")) {
+    // If there are no listeners registered for the server yet, try again in a bit
+    if (tries < MAX_TRIES_PER_SERVER) {
+      timeouts.set(
+        alert.id,
+        setTimeout(() => broadcastExpiredVCAlert(alert, tries + 1), 1 * MINUTES),
+      );
+    }
+    return;
+  }
+  emitGuildEvent(alert.guild_id, "expiredVCAlert", [alert]);
+}
+
+export async function runExpiringVCAlertsLoop() {
+  console.log("[EXPIRING VCALERTS LOOP] Clearing old timeouts");
+  for (const timeout of timeouts.values()) {
+    clearTimeout(timeout);
+  }
+
+  console.log("[EXPIRING VCALERTS LOOP] Setting timeouts for expiring vcalerts");
+  const expiringVCAlerts = await getVCAlertsRepository().getSoonExpiringAlerts(LOOP_INTERVAL);
+  for (const alert of expiringVCAlerts) {
+    const remaining = Math.max(0, moment.utc(alert.expires_at!).diff(moment.utc()));
+    timeouts.set(
+      alert.id,
+      setTimeout(() => broadcastExpiredVCAlert(alert), remaining),
+    );
+  }
+
+  console.log("[EXPIRING VCALERTS LOOP] Scheduling next loop");
+  setTimeout(() => runExpiringVCAlertsLoop(), LOOP_INTERVAL);
+}
+
+export function registerExpiringVCAlert(alert: VCAlert) {
+  clearExpiringVCAlert(alert);
+
+  console.log("[EXPIRING VCALERTS LOOP] Registering new expiring vcalert");
+  const remaining = Math.max(0, moment.utc(alert.expires_at!).diff(moment.utc()));
+  if (remaining > LOOP_INTERVAL) {
+    return;
+  }
+
+  timeouts.set(
+    alert.id,
+    setTimeout(() => broadcastExpiredVCAlert(alert), remaining),
+  );
+}
+
+export function clearExpiringVCAlert(alert: VCAlert) {
+  console.log("[EXPIRING VCALERTS LOOP] Clearing expiring vcalert");
+  if (timeouts.has(alert.id)) {
+    clearTimeout(timeouts.get(alert.id)!);
+  }
+}