feat: Document subscriptions (#3834)

Co-authored-by: Tom Moor <tom.moor@gmail.com>

server/commands/subscriptionCreator.ts

@@ -0,0 +1,74 @@
+import { Transaction } from "sequelize";
+import { Subscription, Event, User } from "@server/models";
+
+type Props = {
+  /** The user creating the subscription */
+  user: User;
+  /** The document to subscribe to */
+  documentId?: string;
+  /** Event to subscribe to */
+  event: string;
+  /** The IP address of the incoming request */
+  ip: string;
+  /** Whether the subscription should be restored if it exists in a deleted state  */
+  resubscribe?: boolean;
+  transaction: Transaction;
+};
+
+/**
+ * This command creates a subscription of a user to a document.
+ *
+ * @returns The subscription that was created
+ */
+export default async function subscriptionCreator({
+  user,
+  documentId,
+  event,
+  ip,
+  resubscribe = true,
+  transaction,
+}: Props): Promise<Subscription> {
+  const [subscription, created] = await Subscription.findOrCreate({
+    where: {
+      userId: user.id,
+      documentId,
+      event,
+    },
+    transaction,
+    // Previous subscriptions are soft-deleted, we want to know about them here
+    paranoid: false,
+  });
+
+  // If the subscription was deleted, then just restore the existing row.
+  if (subscription.deletedAt && resubscribe) {
+    subscription.restore({ transaction });
+
+    await Event.create(
+      {
+        name: "subscriptions.create",
+        modelId: subscription.id,
+        actorId: user.id,
+        userId: user.id,
+        documentId,
+        ip,
+      },
+      { transaction }
+    );
+  }
+
+  if (created) {
+    await Event.create(
+      {
+        name: "subscriptions.create",
+        modelId: subscription.id,
+        actorId: user.id,
+        userId: user.id,
+        documentId,
+        ip,
+      },
+      { transaction }
+    );
+  }
+
+  return subscription;
+}