chore: Refactoring event processors and service architecture (#2495)

server/queues/processors/debouncer.js

@@ -0,0 +1,45 @@
+// @flow
+import { Document } from "../../models";
+import { globalEventQueue } from "../../queues";
+import type { Event } from "../../types";
+
+export default class DebounceProcessor {
+  async on(event: Event) {
+    switch (event.name) {
+      case "documents.update": {
+        globalEventQueue.add(
+          {
+            ...event,
+            name: "documents.update.delayed",
+          },
+          {
+            delay: 5 * 60 * 1000,
+            removeOnComplete: true,
+          }
+        );
+        break;
+      }
+      case "documents.update.delayed": {
+        const document = await Document.findByPk(event.documentId);
+
+        // If the document has been deleted then prevent further processing
+        if (!document) return;
+
+        // If the document has been updated since we initially queued the delayed
+        // event then abort, there must be another updated event in the queue –
+        // this functions as a simple distributed debounce.
+        if (document.updatedAt > new Date(event.createdAt)) return;
+
+        globalEventQueue.add(
+          {
+            ...event,
+            name: "documents.update.debounced",
+          },
+          { removeOnComplete: true }
+        );
+        break;
+      }
+      default:
+    }
+  }
+}