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Yankai Zhu
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Added backend events API
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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/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, fetchEvent, filterInPlace, replaceInPlace } from '../data/eventData';
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interface ChangesEntry {
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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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interface FacebookWebhookNotificationEntry {
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id: string;
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changes: ChangesEntry[];
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}
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interface FacebookWebhookNotification {
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entry: FacebookWebhookNotificationEntry[];
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object: string;
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}
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const verifySignature = (rawBody: Buffer, signatureHeader?: string): 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 (!req.rawBody || typeof signature !== "string" || !verifySignature(req.rawBody, signature)) {
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return res.sendStatus(401);
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}
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const notif: FacebookWebhookNotification = req.body;
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if (!notif || !notif.entry || notif.object !== "page" || notif.entry.length === 0) {
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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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if (change.value.verb === "delete") {
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// we need filter *in place* because all imports are immutable (the REAL const)
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filterInPlace(eventInfo, (val, index, arr) => val.id !== change.value.event_id);
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} else {
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try {
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const newEvent = await fetchEvent(change.value.event_id);
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replaceInPlace(eventInfo, (val, index, arr) => val.id === change.value.event_id, newEvent);
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} catch(err) {
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console.log(`Wasn't able to update event for some reason: ${err}`);
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}
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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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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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// We are altering the array in place, pray we do not alter it from another thread
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// I don't even know if concurrent modification exception is a thing in JS
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// Maybe this is a single threaded moment :icant:
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export function filterInPlace<T>(
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arr: T[],
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predicate: (value: T, index: number, array: T[]) => boolean
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): T[] {
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let write = 0;
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for (let read = 0; read < arr.length; read++) {
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const val = arr[read];
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if (predicate(val, read, arr)) {
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arr[write++] = val;
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}
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}
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arr.length = write;
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return arr;
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}
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// This one is definitely not thread safe lmao
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// TODO fix with a mutex probably
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export function replaceInPlace<T>(
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arr: T[],
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predicate: (value: T, index: number, array: T[]) => boolean,
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replacement: T
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): number {
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const idx = arr.findIndex(predicate);
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if (idx !== -1) arr[idx] = replacement;
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return idx;
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}
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// we LOVE global variables
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export let eventInfo: EventInfo[] = [];
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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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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: FacebookEventsResponse = await response.json();
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if (!res || !res.data) {
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console.log("No events found...");
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return;
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}
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const processed = res.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 ?? "Everything everywhere all at once!!!",
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e.cover?.source || "/images/events/default_event.jpg"
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)
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);
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eventInfo = 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: FacebookEvent = await response.json();
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if (!res) {
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throw new Error(`Couldn't get details for event ${id}`);
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}
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return new EventInfo(
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res.id,
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res.name,
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res.start_time,
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res.end_time,
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res.place?.name ?? "Everything everywhere all at once!!!",
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res.cover?.source || "/images/events/default_event.jpg"
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);
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}

‎backend/src/index.ts‎

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@@ -2,18 +2,39 @@ 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 { 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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await fetchEvents();
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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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console.error("Error fetching events:", 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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app.use(pingRoute);
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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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const app: Express = express();
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const port = process.env.PORT || 9000;
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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.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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}

‎backend/src/types/http/index.d.ts‎

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import "http";
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declare module "http" {
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interface IncomingMessage {
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rawBody?: Buffer;
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}
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}

‎backend/tsconfig.json‎

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// "baseUrl": "./", /* Specify the base directory to resolve non-relative module names. */
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// "paths": {}, /* Specify a set of entries that re-map imports to additional lookup locations. */
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// "rootDirs": [], /* Allow multiple folders to be treated as one when resolving modules. */
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// "typeRoots": [], /* Specify multiple folders that act like './node_modules/@types'. */
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"typeRoots": ["./src/types"], /* Specify multiple folders that act like './node_modules/@types'. */
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// "types": [], /* Specify type package names to be included without being referenced in a source file. */
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// "allowUmdGlobalAccess": true, /* Allow accessing UMD globals from modules. */
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// "moduleSuffixes": [], /* List of file name suffixes to search when resolving a module. */

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