server.js

import fastify from "fastify";
import rawBody from 'fastify-raw-body';
import { InteractionResponseType, InteractionType, verifyKey } from "discord-interactions";

import { SLAP_COMMAND, INVITE_COMMAND } from './commands.js';

const INVITE_URL = `https://discord.com/oauth2/authorize?client_id=${process.env.APPLICATION_ID}&scope=applications.commands`;

const server = fastify({
    logger: true,
});

server.register(rawBody, {
    runFirst: true,
});

server.get("/", (request, response) => {
    server.log.info("Handling GET request");
});

server.addHook('preHandler', async (request, response) => {
    // We don't want to check GET requests to our root url
    if (request.method === 'POST') {
        const signature = request.headers['x-signature-ed25519'];
        const timestamp = request.headers['x-signature-timestamp'];
        const isValidRequest = verifyKey(
            request.rawBody,
            signature,
            timestamp,
            process.env.PUBLIC_KEY
        );
        if (!isValidRequest) {
            server.log.info('Invalid Request');
            return response.status(401).send({ error: 'Bad request signature ' });
        }
    }
});

server.post("/", async (request, response) => {
    const message = request.body;

    if (message.type === InteractionType.PING) {
        server.log.info("Handling Ping request");
        response.send({
            type: InteractionResponseType.PONG,
        });
    } else if (message.type === InteractionType.APPLICATION_COMMAND) {
        switch (message.data.name.toLowerCase()) {
            case SLAP_COMMAND.name.toLowerCase():
                response.status(200).send({
                    type: InteractionResponseType.CHANNEL_MESSAGE_WITH_SOURCE,
                    data: {
                        content: `*<@${message.member.user.id}> slaps <@${message.data.options[0].value}> around a bit with a large trout*`,
                    },
                });
                server.log.info('Slap Request');
                break;
            case INVITE_COMMAND.name.toLowerCase():
                response.status(200).send({
                    type: InteractionResponseType.CHANNEL_MESSAGE_WITH_SOURCE,
                    data: {
                        content: INVITE_URL,
                        flags: 64,
                    },
                });
                server.log.info('Invite request');
                break;
            default:
                server.log.error('Unknown Command');
                response.status(400).send({ error: 'Unknown Type' });
                break;
        }
    } else {
        server.log.error("Unknown Type");
        response.status(400).send({ error: "Unknown Type" });
    }
});

server.listen(3000, async (error, address) => {
    if (error) {
        server.log.error(error);
        process.exit(1);
    }
    server.log.info(`server listening on ${address}`);
});