Set up SSE (Server sent events) for event signup counts (#776)

* Create getActiveEvents method in Event service and its tests

Created the getActiveEvents to fetch present events

* Create getActiveReservationsCount method that uses previous created method that returns total count of reservations

Also did some documentation for methods that this method uses.

Created tests that are required

* Create /events/reservations/stream SSE endpoint

This endpoint creates a stream with keep-alive headers that continuously streams the number of active reservations.

* Update payload to follow SSE requirements, also now returns a JSON payload

* Why is my java files in here lol...removed NumbersApp.java

* Update doc for schema and methods involved

* Add generated routes

server/src/data-layer/models/firebase.ts

@@ -171,13 +171,13 @@ export interface Event {
    */
   location: string
   /**
-   * The start date of the event.
+   * The signup period start date.
    * Note that this date is in UTC time.
-   * Use the same start and end day to show that its a 1 day event.
+   * Use the same start and end date to indicate a 1 day signup period.
    */
   start_date: Timestamp
   /**
-   * The end date of the event.
+   * The signup period end date.
    * Note that this date is in UTC time.
    */
   end_date: Timestamp

server/src/data-layer/services/EventService.test.ts

@@ -6,6 +6,7 @@ import {
 } from "data-layer/adapters/DateUtils"
 import { Event, EventReservation } from "data-layer/models/firebase"
 import FirestoreCollections from "data-layer/adapters/FirestoreCollections"
+import { Timestamp } from "firebase-admin/firestore"
 
 const eventService = new EventService()
 
@@ -26,6 +27,13 @@ const event2: Event = {
   start_date: startDate,
   end_date: endDate
 }
+const now = new Date(Date.now())
+const futureEvent: Event = {
+  title: "Scheduled event",
+  location: "Future event",
+  start_date: Timestamp.fromDate(new Date(now.getUTCFullYear() + 1, 1, 1)),
+  end_date: Timestamp.fromDate(new Date(now.getUTCFullYear() + 1, 1, 1))
+}
 
 const reservation1: EventReservation = {
   first_name: "John",
@@ -73,6 +81,19 @@ describe("EventService integration tests", () => {
     }).toEqual(event1)
   })
 
+  it("Should be able to get current existing events", async () => {
+    // Create past events
+    await eventService.createEvent(event1)
+    await eventService.createEvent(event2)
+    // Create a future event
+    const newEvent = await eventService.createEvent(futureEvent)
+
+    const futureEvents = await eventService.getActiveEvents()
+
+    expect(futureEvents.length).toBe(1)
+    expect(futureEvents).toEqual([{ ...futureEvent, id: newEvent.id }])
+  })
+
   it("Should be able to update an event", async () => {
     const newEvent = await eventService.createEvent(event1)
 
@@ -178,6 +199,19 @@ describe("EventService integration tests", () => {
       expect(fetchedReservation).toEqual(reservation1)
     })
 
+    it("Should get the total count of active event reservations", async () => {
+      // An older event shouldn't be counted.
+      const oldEvent = await eventService.createEvent(event1)
+      await eventService.addReservation(oldEvent.id, reservation1)
+      // Should only count reservations for future events
+      const newEvent = await eventService.createEvent(futureEvent)
+      await eventService.addReservation(newEvent.id, reservation1)
+      await eventService.addReservation(newEvent.id, reservation2)
+
+      const count = await eventService.getActiveReservationsCount()
+      expect(count).toBe(2)
+    })
+
     it("Should get all event reservations", async () => {
       const newEvent = await eventService.createEvent(event1)
       await eventService.addReservation(newEvent.id, reservation1)

server/src/data-layer/services/EventService.ts

@@ -1,5 +1,6 @@
 import FirestoreCollections from "data-layer/adapters/FirestoreCollections"
 import FirestoreSubcollections from "data-layer/adapters/FirestoreSubcollections"
+import { DocumentDataWithUid } from "data-layer/models/common"
 import { Event, EventReservation } from "data-layer/models/firebase"
 
 class EventService {
@@ -25,6 +26,24 @@ class EventService {
     return result.data()
   }
 
+  /**
+   * Fetches all events that have a end_date in the future.
+   * Note that "active" means any event that haven't ended yet.
+   *
+   * @returns a list of events that have a end_date that is later to the current date.
+   */
+  public async getActiveEvents(): Promise<DocumentDataWithUid<Event>[]> {
+    const now = new Date(Date.now())
+
+    const result = await FirestoreCollections.events
+      .where("end_date", ">", now) // Only get events that have not ended
+      .get()
+
+    return result.docs.map((doc) => {
+      return { ...(doc.data() as Event), id: doc.id }
+    })
+  }
+
   /**
    * Updates an existing event document by ID with new Event data.
    *
@@ -72,7 +91,10 @@ class EventService {
    * @param reservationId the ID of the reservation document
    * @returns the reservation document
    */
-  public async getReservationById(eventId: string, reservationId: string) {
+  public async getReservationById(
+    eventId: string,
+    reservationId: string
+  ): Promise<EventReservation> {
     const result = await FirestoreSubcollections.reservations(eventId)
       .doc(reservationId)
       .get()
@@ -85,11 +107,29 @@ class EventService {
    * @param eventId the ID of the event document
    * @returns an array of all the event reservation documents
    */
-  public async getAllReservations(eventId: string) {
+  public async getAllReservations(
+    eventId: string
+  ): Promise<EventReservation[]> {
     const result = await FirestoreSubcollections.reservations(eventId).get()
     return result.docs.map((doc) => doc.data())
   }
 
+  /**
+   * Used for the SSE feature to display the total number of active event reservations.
+   * @returns the total number of active event reservations
+   */
+  public async getActiveReservationsCount(): Promise<number> {
+    const currentEvents = await this.getActiveEvents()
+    let total = 0
+    await Promise.all(
+      currentEvents.map(async (event) => {
+        const eventReservations = await this.getAllReservations(event.id)
+        total += eventReservations.length
+      })
+    )
+    return total
+  }
+
   /**
    * Updates an existing reservation document by ID with new EventReservation data.
    *

server/src/service-layer/controllers/EventController.ts

@@ -1,7 +1,16 @@
 import EventService from "data-layer/services/EventService"
 import { EventSignupBody } from "service-layer/request-models/EventRequests"
 import { EventSignupResponse } from "service-layer/response-models/EventResponse"
-import { Body, Controller, Post, Route, SuccessResponse } from "tsoa"
+import {
+  Get,
+  Body,
+  Controller,
+  Post,
+  Route,
+  Request,
+  SuccessResponse
+} from "tsoa"
+import express from "express"
 
 @Route("events")
 export class EventController extends Controller {
@@ -58,4 +67,42 @@ export class EventController extends Controller {
       return { error: "Failed to sign up for event." }
     }
   }
+
+  /**
+   * Streams the signup count for active events signups.
+   * Note that when testing this on swagger, the connection will remain open.
+   */
+  @Get("/reservations/stream")
+  public async streamSignupCounts(
+    @Request() req: express.Request
+  ): Promise<void> {
+    // Set the required headers for SSE
+    req.res.setHeader("Cache-Control", "no-cache")
+    req.res.setHeader("Content-Type", "text/event-stream")
+    req.res.setHeader("Access-Control-Allow-Origin", "*")
+    req.res.setHeader("Connection", "keep-alive")
+    req.res.flushHeaders()
+    const eventService = new EventService()
+
+    const signupCount = await eventService.getActiveReservationsCount() // Fetch the current signup count
+    req.res.write(
+      `data: ${JSON.stringify({ reservation_count: signupCount })}\n\n`
+    )
+
+    // Create something that updates every 5 seconds
+    const interValID = setInterval(async () => {
+      const signupCount = await eventService.getActiveReservationsCount() // Fetch the current signup count
+      // NOTE: We use double new line because SSE requires this to indicate we're ready for the next event
+      // We also need the data: to indicate data payload
+      req.res.write(
+        `data: ${JSON.stringify({ reservation_count: signupCount })}\n\n`
+      ) // res.write() instead of res.send()
+    }, 5000)
+
+    // If the connection drops, stop sending events
+    req.res?.on("close", () => {
+      clearInterval(interValID) // Clear the loop
+      req.res?.end()
+    })
+  }
 }