const DynamoDB = require('../datastore/dynamodb'),
  Request = require('../core/request'),
  App = require('../core/app');

module.exports = function(settings) {
  const { datastore } = settings;

  // load the dynamodb datastore if none is provided
  if (datastore === undefined || typeof datastore === 'string')
    settings.datastore = new DynamoDB(datastore);

  const handler = (cb, event, context, callback) => {
    const app = new App(settings);
    const slack = new Request(app, event);
    const { valid, challenge, code, install_url } = slack;
    const done = () => cb(slack, context, callback);

    // redirect to OAuth
    if (install_url) return context.fail(install_url);

    // OAuth callback from Slack
    if (code) return slack.install().then(done);

    // Failed request verification
    if (!valid) return context.fail('Invalid Request');

    // Events API challenge request
    if (challenge) return context.succeed(challenge);

    // Load workspace data and continue
    return slack.load().then(done);
  };

  return cb => handler.bind(null, cb);
};