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

server/queues/processors/revisions.js

@@ -0,0 +1,37 @@
+// @flow
+import invariant from "invariant";
+import revisionCreator from "../../commands/revisionCreator";
+import { Revision, Document, User } from "../../models";
+import type { DocumentEvent, RevisionEvent } from "../../types";
+
+export default class RevisionsProcessor {
+  async on(event: DocumentEvent | RevisionEvent) {
+    switch (event.name) {
+      case "documents.publish":
+      case "documents.update.debounced": {
+        const document = await Document.findByPk(event.documentId);
+        invariant(document, "Document should exist");
+
+        const previous = await Revision.findLatest(document.id);
+
+        // we don't create revisions if identical to previous revision, this can
+        // happen if a manual revision was created from another service or user.
+        if (
+          previous &&
+          document.text === previous.text &&
+          document.title === previous.title
+        ) {
+          return;
+        }
+
+        const user = await User.findByPk(event.actorId);
+        invariant(user, "User should exist");
+
+        await revisionCreator({ user, document });
+
+        break;
+      }
+      default:
+    }
+  }
+}