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somereticalYankai Zhu
someretical
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Yankai Zhu
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[I2-17] Added backend events API (#53)
* Added backend events API * polished code --------- Co-authored-by: Yankai Zhu <[email protected]>
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‎.gitignore‎

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@@ -35,3 +35,5 @@ yarn-error.log*
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# typescript
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*.tsbuildinfo
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next-env.d.ts
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*.env

‎backend/package-lock.json‎

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‎backend/package.json‎

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"@types/cors": "^2.8.17",
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"@types/express": "^4.17.21",
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"@types/node": "^20.12.13",
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"async-mutex": "^0.5.0",
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"cors": "^2.8.5",
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"dotenv": "^16.4.5",
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"express": "^4.19.2",

‎backend/src/controllers/events.ts‎

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import { RequestHandler } from "express";
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import { eventInfo } from "../data/eventData";
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export const EventsHandler: RequestHandler = (req, res) => {
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res.status(200).json(eventInfo);
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}

‎backend/src/controllers/eventsWebhook.ts‎

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import crypto from "crypto";
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import { RequestHandler } from "express";
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import { eventInfo, eventInfoMutex, fetchEvent } from "../data/eventData";
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import { filterInPlace, replaceInPlace } from "../util";
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interface FacebookWebhookPayload {
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object: string;
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entry: Array<{
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id: string;
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changes: Array<{
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field: string;
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value: {
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event_id: string;
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item: string;
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verb: string;
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};
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}>;
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}>;
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}
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const verifySignature = (
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rawBody: Buffer,
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signatureHeader?: string
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): boolean => {
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if (!signatureHeader) return false;
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const [algo, signature] = signatureHeader.split("=");
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if (algo !== "sha256") return false;
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const expected = crypto
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.createHmac("sha256", process.env.FB_APP_SECRET as string)
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.update(rawBody)
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.digest("hex");
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return crypto.timingSafeEqual(Buffer.from(signature), Buffer.from(expected));
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};
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export const EventsWebhookVerifier: RequestHandler = (req, res) => {
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const mode = req.query["hub.mode"];
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const token = req.query["hub.verify_token"];
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const challenge = req.query["hub.challenge"];
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if (mode === "subscribe" && token === process.env.FB_WEBHOOK_VERIFY_TOKEN) {
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return res.status(200).send(challenge);
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}
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res.sendStatus(403);
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};
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/*
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Sample webhook payload
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https://developers.facebook.com/docs/graph-api/webhooks/getting-started/webhooks-for-pages -- for the outer wrapper
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https://developers.facebook.com/docs/graph-api/webhooks/reference/page/#feed -- for the inner objects
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{
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"object": "page",
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"entry": [
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{
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"id": "PAGE_ID",
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"time": 1623242342342,
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"changes": [
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{
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"field": "events",
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"value": {
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"event_id": "123456789",
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"verb": "create", // also "edit" or "delete"
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"published": 1
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}
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}
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]
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}
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]
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}
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*/
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export const EventsWebhookUpdate: RequestHandler = async (req, res) => {
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const signature = req.headers["x-hub-signature-256"];
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if (
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!req.rawBody ||
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typeof signature !== "string" ||
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!verifySignature(req.rawBody, signature)
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) {
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return res.sendStatus(401);
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}
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const notif: FacebookWebhookPayload = req.body;
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if (
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!notif ||
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!notif.entry ||
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notif.object !== "page" ||
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notif.entry.length === 0
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) {
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return res.sendStatus(400);
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}
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for (const entry of notif.entry) {
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if (entry.id !== process.env.FB_EVENT_PAGE_ID) continue;
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for (const change of entry.changes) {
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if (change.field !== "feed" || change.value.item !== "event") continue;
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try {
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if (change.value.verb === "delete") {
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await eventInfoMutex.runExclusive(() =>
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filterInPlace(eventInfo, (val) => val.id !== change.value.event_id)
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);
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console.log(`Deleted event: ${change.value.event_id}`);
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} else if (change.value.verb === "edit") {
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const newEvent = await fetchEvent(change.value.event_id);
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eventInfoMutex.runExclusive(() =>
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replaceInPlace(
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eventInfo,
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(val) => val.id === change.value.event_id,
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newEvent
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)
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);
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console.log(`Edited event: ${change.value.event_id}`);
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} else if (change.value.verb === "add") {
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const newEvent = await fetchEvent(change.value.event_id);
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await eventInfoMutex.runExclusive(() => eventInfo.push(newEvent));
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console.log(`Added event: ${change.value.event_id}`);
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} else {
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console.warn(
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`Unknown verb "${change.value.verb}" for event ${change.value.event_id}`
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);
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}
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} catch (err) {
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console.error(
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`Error processing event: ${change.value.event_id}:\n${err}`
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);
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return res.sendStatus(500);
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}
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}
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}
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res.sendStatus(200);
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};

‎backend/src/data/eventData.ts‎

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import { Mutex } from "async-mutex";
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import { inspect } from "util";
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import { FacebookError, Result, ResultType } from "../util";
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class EventInfo {
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// god forbid a class have public members
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public id: string;
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public title: string;
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public startTime: string;
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public endTime?: string;
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public location: string;
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public imageUrl: string;
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public link: string;
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constructor(
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id: string,
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title: string,
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startTime: string,
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endTime: string | undefined,
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location: string,
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imageUrl: string
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) {
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this.id = id;
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this.title = title;
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this.startTime = startTime;
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this.endTime = endTime;
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this.location = location;
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this.imageUrl = imageUrl;
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// would use link as getter but getters are not enumerable so it doesn't appear in JSON.stringify :skull:
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// maybe a cursed fix would be to use Object.defineProperty LOL
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this.link = `https://www.facebook.com/events/${id}`;
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}
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}
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interface FacebookEvent {
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id: string;
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name: string;
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cover?: { source: string };
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place?: { name: string };
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start_time: string;
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end_time?: string;
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}
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interface FacebookEventsResponse {
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data: FacebookEvent[];
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}
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// this isn't in .env for different module compatiblity
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const FB_API_VERSION = "v23.0";
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const DEFAULT_EVENT_LOCATION = "Everything everywhere all at once!!!";
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const DEFAULT_EVENT_IMAGE = "/images/events/default_event.jpg";
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// we LOVE global variables
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export const eventInfoMutex = new Mutex();
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export const eventInfo: EventInfo[] = [];
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export async function fetchEvents() {
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const response = await fetch(
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`https://graph.facebook.com/${FB_API_VERSION}/${process.env.FB_EVENT_PAGE_ID}/events?access_token=${process.env.FB_ACCESS_TOKEN}&fields=id,name,cover,place,start_time,end_time`
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);
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const res: Result<FacebookEventsResponse, FacebookError> = await response.json();
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if (!res || res.type === ResultType.Err) {
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console.log(`No events found...\n${res}`);
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return [];
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}
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const processed = res.value.data.map(
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(e) =>
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new EventInfo(
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e.id,
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e.name,
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e.start_time,
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e.end_time,
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e.place?.name ?? DEFAULT_EVENT_LOCATION,
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e.cover?.source ?? DEFAULT_EVENT_IMAGE
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)
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);
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return processed;
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}
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export async function fetchEvent(id: string) {
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const response = await fetch(
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`https://graph.facebook.com/${FB_API_VERSION}/${id}?access_token=${process.env.FB_ACCESS_TOKEN}&fields=id,name,cover,place,start_time,end_time`
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);
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const res: Result<FacebookEvent, FacebookError> = await response.json();
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if (!res || res.type === ResultType.Err) {
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throw new Error(
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`Couldn't fetch details for event ${id}\n${inspect(
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Object.getOwnPropertyDescriptor(res, "error")?.value
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)}`
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);
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}
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return new EventInfo(
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res.value.id,
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res.value.name,
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res.value.start_time,
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res.value.end_time,
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res.value.place?.name ?? DEFAULT_EVENT_LOCATION,
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res.value.cover?.source ?? DEFAULT_EVENT_IMAGE
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);
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}

‎backend/src/index.ts‎

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@@ -2,18 +2,41 @@ import express, { Express } from "express";
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import cors from "cors";
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import dotenv from "dotenv";
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import pingRoute from "./routes/ping";
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import eventsRoute from "./routes/events";
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import eventsWebhookRoute from "./routes/eventsWebhook";
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import { eventInfo, eventInfoMutex, fetchEvents } from "./data/eventData";
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dotenv.config();
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const app: Express = express();
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const port = process.env.PORT || 9000;
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(async () => {
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try {
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const events = await fetchEvents();
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eventInfoMutex.runExclusive(() => eventInfo.concat(events));
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console.log("Events fetched successfully");
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} catch (error) {
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// do we ungracefully bail out here???
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// could just load from a backup file instead
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console.error("Error fetching events on startup:", error);
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}
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// Middleware
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app.use(express.json());
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app.use(cors());
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const app: Express = express();
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const port = process.env.PORT || 9000;
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app.use(pingRoute);
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// Middleware
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app.use(
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express.json({
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verify: (req, res, buf) => {
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req.rawBody = buf;
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},
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})
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);
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app.use(cors());
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app.listen(port, () => {
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console.log(`Server successfully started on port ${port}`);
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});
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app.use(pingRoute);
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app.use(eventsWebhookRoute);
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app.use(eventsRoute);
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app.listen(port, () => {
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console.log(`Server successfully started on port ${port}`);
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});
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})();

‎backend/src/routes/events.ts‎

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import { Router } from "express";
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import { EventsHandler } from "../controllers/events";
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const router = Router();
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router.get("/events", EventsHandler);
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export default router;

‎backend/src/routes/eventsWebhook.ts‎

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import { Router } from "express";
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import { EventsWebhookUpdate, EventsWebhookVerifier } from "../controllers/eventsWebhook";
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const router = Router();
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router.post("/eventsWebhook", EventsWebhookUpdate);
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router.get("/eventsWebhook", EventsWebhookVerifier);
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export default router;

‎backend/src/types/express/index.d.ts‎

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import "express";
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declare module "express-serve-static-core" {
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interface Request {
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rawBody?: Buffer;
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}
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interface IncomingMessage {
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rawBody?: Buffer;
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}
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}

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