index.js

const { Probot } = require("probot");
const { resolve } = require("probot/lib/helpers/resolve-app-function");
const { findPrivateKey } = require("probot/lib/helpers/get-private-key");
const { template } = require("./views/probot");

let probot;

const loadProbot = (appFn) => {
  probot =
    probot ||
    new Probot({
      id: process.env.APP_ID,
      secret: process.env.WEBHOOK_SECRET,
      privateKey: findPrivateKey(),
    });

  if (typeof appFn === "string") {
    appFn = resolve(appFn);
  }

  probot.load(appFn);

  return probot;
};

const lowerCaseKeys = (obj = {}) =>
  Object.keys(obj).reduce(
    (accumulator, key) =>
      Object.assign(accumulator, { [key.toLocaleLowerCase()]: obj[key] }),
    {}
  );

module.exports.serverless = (appFn) => {
  return async (event, context) => {
    // 🤖 A friendly homepage if there isn't a payload
    if (event.httpMethod === "GET" && event.path === "/probot") {
      const res = {
        statusCode: 200,
        headers: {
          "Content-Type": "text/html",
        },
        body: template,
      };
      return res;
    }

    // Otherwise let's listen handle the payload
    probot = probot || loadProbot(appFn);

    // Ends function immediately after callback
    context.callbackWaitsForEmptyEventLoop = false;

    // Determine incoming webhook event type
    const headers = lowerCaseKeys(event.headers);
    const e = headers["x-github-event"];
    if (!e) {
      return {
        statusCode: 400,
        body: "X-Github-Event header is missing",
      };
    }

    // If body is expected to be base64 encoded, decode it and continue
    if (event.isBase64Encoded) {
      event.body = Buffer.from(event.body, "base64").toString("utf8");
    }

    // Convert the payload to an Object if API Gateway stringifies it
    event.body =
      typeof event.body === "string" ? JSON.parse(event.body) : event.body;

    // Bail for null body
    if (!event.body) {
      return {
        statusCode: 400,
        body: "Event body is null.",
      };
    }

    // Do the thing
    console.log(
      `Received event ${e}${event.body.action ? "." + event.body.action : ""}`
    );
    if (event) {
      try {
        await probot.receive({
          name: e,
          payload: event.body,
        });
        return {
          statusCode: 200,
          body: JSON.stringify({
            message: `Received ${e}.${event.body.action}`,
          }),
        };
      } catch (err) {
        console.error(err);
        return {
          statusCode: 500,
          body: JSON.stringify(err),
        };
      }
    } else {
      console.error({ event, context });
      throw new Error("unknown error");
    }
  };
};