@dillonkearns/elm-graphql/examples/src/subscription/node_modules/webpack-serve/lib/app.js

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const getPort = require('get-port');
const Koa = require('koa');
const series = require('p-series');

const ContentMiddleware = require('./middleware/ContentMiddleware');
const WebpackMiddleware = require('./middleware/WebpackMiddleware');

const { bind, getServer } = require('./server');

module.exports = {
  getApp(options) {
    const app = new Koa();
    const contentMiddleware = new ContentMiddleware(app, options);
    const webpackMiddleware = new WebpackMiddleware(app, options);
    const middleware = {
      content: contentMiddleware.call,
      webpack: webpackMiddleware.call,
    };
    const server = getServer(app, options);
    const { start, stop } = module.exports;

    bind(server, options);

    const result = Object.assign(app, {
      server,
      start: start.bind(null, app, middleware, server, options),
      stop: stop.bind(null, webpackMiddleware, server),
    });

    return result;
  },

  start(app, middleware, server, options) {
    const { host, port } = options;
    let promise;

    if (options.port === 0) {
      promise = Promise.resolve(0);
    } else {
      promise = getPort({ port, host });
    }

    return promise.then((freePort) => {
      if (typeof options.add === 'function') {
        options.add(app, middleware, options);
      }

      return series([
        // memo'd, so even if it's called in options.add, we're safe
        () => middleware.webpack.call(),
        () => middleware.content.call(),
        () =>
          new Promise((resolve, reject) => {
            server.listen(freePort, host, (e) => {
              /* istanbul ignore if */
              if (e) {
                reject(e);
              }
              resolve(server);
            });
          }),
      ]);
    });
  },

  stop(webpackMiddleware, server, fn) {
    server.kill(() => {
      const { called, koaMiddleware, state } = webpackMiddleware;
      /* istanbul ignore else */
      if (called) {
        state.then(() => koaMiddleware.close(fn));
      }
    });
  },
};