feat: Automatic invite reminder email (#3354)

* feat: Add user flags concept, for tracking bits on a user

* feat: Example flag usage for user invite resend abuse

* wip

* test

* fix: Set correct flag

server/queues/tasks/InviteReminderTask.test.ts

@@ -0,0 +1,37 @@
+import { subDays } from "date-fns";
+import InviteReminderEmail from "@server/emails/templates/InviteReminderEmail";
+import { buildInvite } from "@server/test/factories";
+import { flushdb } from "@server/test/support";
+import InviteReminderTask from "./InviteReminderTask";
+
+beforeEach(() => flushdb());
+
+describe("InviteReminderTask", () => {
+  it("should not destroy documents not deleted", async () => {
+    const spy = jest.spyOn(InviteReminderEmail, "schedule");
+
+    // too old
+    await buildInvite({
+      createdAt: subDays(new Date(), 3.5),
+    });
+
+    // too new
+    await buildInvite({
+      createdAt: new Date(),
+    });
+
+    // should send reminder
+    await buildInvite({
+      createdAt: subDays(new Date(), 2.5),
+    });
+
+    const task = new InviteReminderTask();
+    await task.perform();
+
+    // running twice to make sure the email is only sent once
+    await task.perform();
+
+    expect(spy).toHaveBeenCalledTimes(1);
+    spy.mockRestore();
+  });
+});