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[I2-17] Added backend events API#53

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Merged
Domin0de merged 2 commits intoqafromI2-17/events-api
Jul 9, 2025
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2 changes: 2 additions & 0 deletions.gitignore
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Expand Up@@ -35,3 +35,5 @@ yarn-error.log*
# typescript
*.tsbuildinfo
next-env.d.ts

*.env
14 changes: 14 additions & 0 deletionsbackend/package-lock.json
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1 change: 1 addition & 0 deletionsbackend/package.json
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Expand Up@@ -9,6 +9,7 @@
"@types/cors": "^2.8.17",
"@types/express": "^4.17.21",
"@types/node": "^20.12.13",
"async-mutex": "^0.5.0",
"cors": "^2.8.5",
"dotenv": "^16.4.5",
"express": "^4.19.2",
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6 changes: 6 additions & 0 deletionsbackend/src/controllers/events.ts
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import { RequestHandler } from "express";
import { eventInfo } from "../data/eventData";

export const EventsHandler: RequestHandler = (req, res) => {
res.status(200).json(eventInfo);
}
137 changes: 137 additions & 0 deletionsbackend/src/controllers/eventsWebhook.ts
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import crypto from "crypto";
import { RequestHandler } from "express";
import { eventInfo, eventInfoMutex, fetchEvent } from "../data/eventData";
import { filterInPlace, replaceInPlace } from "../util";

interface FacebookWebhookPayload {
object: string;
entry: Array<{
id: string;
changes: Array<{
field: string;
value: {
event_id: string;
item: string;
verb: string;
};
}>;
}>;
}

const verifySignature = (
rawBody: Buffer,
signatureHeader?: string
): boolean => {
if (!signatureHeader) return false;
const [algo, signature] = signatureHeader.split("=");
if (algo !== "sha256") return false;

const expected = crypto
.createHmac("sha256", process.env.FB_APP_SECRET as string)
.update(rawBody)
.digest("hex");

return crypto.timingSafeEqual(Buffer.from(signature), Buffer.from(expected));
};

export const EventsWebhookVerifier: RequestHandler = (req, res) => {
const mode = req.query["hub.mode"];
const token = req.query["hub.verify_token"];
const challenge = req.query["hub.challenge"];

if (mode === "subscribe" && token === process.env.FB_WEBHOOK_VERIFY_TOKEN) {
return res.status(200).send(challenge);
}

res.sendStatus(403);
};

/*
Sample webhook payload
https://developers.facebook.com/docs/graph-api/webhooks/getting-started/webhooks-for-pages -- for the outer wrapper
https://developers.facebook.com/docs/graph-api/webhooks/reference/page/#feed -- for the inner objects

{
"object": "page",
"entry": [
{
"id": "PAGE_ID",
"time": 1623242342342,
"changes": [
{
"field": "events",
"value": {
"event_id": "123456789",
"verb": "create", // also "edit" or "delete"
"published": 1
}
}
]
}
]
}
*/

export const EventsWebhookUpdate: RequestHandler = async (req, res) => {
const signature = req.headers["x-hub-signature-256"];
if (
!req.rawBody ||
typeof signature !== "string" ||
!verifySignature(req.rawBody, signature)
) {
return res.sendStatus(401);
}

const notif: FacebookWebhookPayload = req.body;
if (
!notif ||
!notif.entry ||
notif.object !== "page" ||
notif.entry.length === 0
) {
return res.sendStatus(400);
}

for (const entry of notif.entry) {
if (entry.id !== process.env.FB_EVENT_PAGE_ID) continue;

for (const change of entry.changes) {
if (change.field !== "feed" || change.value.item !== "event") continue;

try {
if (change.value.verb === "delete") {
await eventInfoMutex.runExclusive(() =>
filterInPlace(eventInfo, (val) => val.id !== change.value.event_id)
);
console.log(`Deleted event: ${change.value.event_id}`);
} else if (change.value.verb === "edit") {
const newEvent = await fetchEvent(change.value.event_id);

eventInfoMutex.runExclusive(() =>
replaceInPlace(
eventInfo,
(val) => val.id === change.value.event_id,
newEvent
)
);
console.log(`Edited event: ${change.value.event_id}`);
} else if (change.value.verb === "add") {
const newEvent = await fetchEvent(change.value.event_id);
await eventInfoMutex.runExclusive(() => eventInfo.push(newEvent));
console.log(`Added event: ${change.value.event_id}`);
} else {
console.warn(
`Unknown verb "${change.value.verb}" for event ${change.value.event_id}`
);
}
} catch (err) {
console.error(
`Error processing event: ${change.value.event_id}:\n${err}`
);
return res.sendStatus(500);
}
}
}

res.sendStatus(200);
};
106 changes: 106 additions & 0 deletionsbackend/src/data/eventData.ts
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import { Mutex } from "async-mutex";
import { inspect } from "util";
import { FacebookError, Result, ResultType } from "../util";

class EventInfo {
// god forbid a class have public members
public id: string;
public title: string;
public startTime: string;
public endTime?: string;
public location: string;
public imageUrl: string;
public link: string;

constructor(
id: string,
title: string,
startTime: string,
endTime: string | undefined,
location: string,
imageUrl: string
) {
this.id = id;
this.title = title;
this.startTime = startTime;
this.endTime = endTime;
this.location = location;
this.imageUrl = imageUrl;
// would use link as getter but getters are not enumerable so it doesn't appear in JSON.stringify :skull:
// maybe a cursed fix would be to use Object.defineProperty LOL
this.link = `https://www.facebook.com/events/${id}`;
}
}

interface FacebookEvent {
id: string;
name: string;
cover?: { source: string };
place?: { name: string };
start_time: string;
end_time?: string;
}

interface FacebookEventsResponse {
data: FacebookEvent[];
}

// this isn't in .env for different module compatiblity
const FB_API_VERSION = "v23.0";
const DEFAULT_EVENT_LOCATION = "Everything everywhere all at once!!!";
const DEFAULT_EVENT_IMAGE = "/images/events/default_event.jpg";

// we LOVE global variables
export const eventInfoMutex = new Mutex();
export const eventInfo: EventInfo[] = [];

export async function fetchEvents() {
const response = await fetch(
`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`
);

const res: Result<FacebookEventsResponse, FacebookError> = await response.json();
if (!res || res.type === ResultType.Err) {
console.log(`No events found...\n${res}`);
return [];
}

const processed = res.value.data.map(
(e) =>
new EventInfo(
e.id,
e.name,
e.start_time,
e.end_time,
e.place?.name ?? DEFAULT_EVENT_LOCATION,
e.cover?.source ?? DEFAULT_EVENT_IMAGE
)
);

return processed;
}

export async function fetchEvent(id: string) {
const response = await fetch(
`https://graph.facebook.com/${FB_API_VERSION}/${id}?access_token=${process.env.FB_ACCESS_TOKEN}&fields=id,name,cover,place,start_time,end_time`
);

const res: Result<FacebookEvent, FacebookError> = await response.json();

if (!res || res.type === ResultType.Err) {
throw new Error(
`Couldn't fetch details for event ${id}\n${inspect(
Object.getOwnPropertyDescriptor(res, "error")?.value
)}`
);
}

return new EventInfo(
res.value.id,
res.value.name,
res.value.start_time,
res.value.end_time,
res.value.place?.name ?? DEFAULT_EVENT_LOCATION,
res.value.cover?.source ?? DEFAULT_EVENT_IMAGE
);
}
41 changes: 32 additions & 9 deletionsbackend/src/index.ts
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Expand Up@@ -2,18 +2,41 @@ import express, { Express } from "express";
import cors from "cors";
import dotenv from "dotenv";
import pingRoute from "./routes/ping";
import eventsRoute from "./routes/events";
import eventsWebhookRoute from "./routes/eventsWebhook";
import { eventInfo, eventInfoMutex, fetchEvents } from "./data/eventData";

dotenv.config();

const app: Express = express();
const port = process.env.PORT || 9000;
(async () => {
try {
const events = await fetchEvents();
eventInfoMutex.runExclusive(() => eventInfo.concat(events));
console.log("Events fetched successfully");
} catch (error) {
// do we ungracefully bail out here???
// could just load from a backup file instead
console.error("Error fetching events on startup:", error);
}

// Middleware
app.use(express.json());
app.use(cors());
const app: Express = express();
const port = process.env.PORT || 9000;

app.use(pingRoute);
// Middleware
app.use(
express.json({
verify: (req, res, buf) => {
req.rawBody = buf;
},
})
);
app.use(cors());

app.listen(port, () => {
console.log(`Server successfully started on port ${port}`);
});
app.use(pingRoute);
app.use(eventsWebhookRoute);
app.use(eventsRoute);

app.listen(port, () => {
console.log(`Server successfully started on port ${port}`);
});
})();
8 changes: 8 additions & 0 deletionsbackend/src/routes/events.ts
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import { Router } from "express";
import { EventsHandler } from "../controllers/events";

const router = Router();

router.get("/events", EventsHandler);

export default router;
9 changes: 9 additions & 0 deletionsbackend/src/routes/eventsWebhook.ts
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import { Router } from "express";
import { EventsWebhookUpdate, EventsWebhookVerifier } from "../controllers/eventsWebhook";

const router = Router();

router.post("/eventsWebhook", EventsWebhookUpdate);
router.get("/eventsWebhook", EventsWebhookVerifier);

export default router;
11 changes: 11 additions & 0 deletionsbackend/src/types/express/index.d.ts
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import "express";

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

interface IncomingMessage {
rawBody?: Buffer;
}
}
7 changes: 7 additions & 0 deletionsbackend/src/types/http/index.d.ts
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import "http";

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