/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 */
'use strict';

const querystring = require('querystring');
const url = require('url');

/**
 * Attaches a WebSocket based connection to the Packager to expose
 * Hot Module Replacement updates to the simulator.
 */
function attachHMRServer({httpServer, path, packagerServer}) {
  let client = null;

  function disconnect() {
    client = null;
    packagerServer.setHMRFileChangeListener(null);
  }

  // Returns a promise with the full list of dependencies and the shallow
  // dependencies each file on the dependency list has for the give platform
  // and entry file.
  function getDependencies(platform, bundleEntry) {
    return packagerServer.getDependencies({
      platform: platform,
      dev: true,
      entryFile: bundleEntry,
    }).then(response => {
      // for each dependency builds the object:
      // `{path: '/a/b/c.js', deps: ['modA', 'modB', ...]}`
      return Promise.all(Object.values(response.dependencies).map(dep => {
        if (dep.isAsset() || dep.isAsset_DEPRECATED() || dep.isJSON()) {
          return Promise.resolve({path: dep.path, deps: []});
        }
        return packagerServer.getShallowDependencies(dep.path)
          .then(deps => {
            return {
              path: dep.path,
              deps,
            };
          });
      }))
      .then(deps => {
        // list with all the dependencies the bundle entry has
        const dependenciesCache = response.dependencies.map(dep => dep.path);

        // map that indicates the shallow dependency each file included on the
        // bundle has
        const shallowDependencies = {};
        deps.forEach(dep => shallowDependencies[dep.path] = dep.deps);

        return {dependenciesCache, shallowDependencies};
      });
    });
  }

  const WebSocketServer = require('ws').Server;
  const wss = new WebSocketServer({
    server: httpServer,
    path: path,
  });

  console.log('[Hot Module Replacement] Server listening on', path);
  wss.on('connection', ws => {
    console.log('[Hot Module Replacement] Client connected');
    const params = querystring.parse(url.parse(ws.upgradeReq.url).query);

    getDependencies(params.platform, params.bundleEntry)
      .then(({dependenciesCache, shallowDependencies}) => {
        client = {
          ws,
          platform: params.platform,
          bundleEntry: params.bundleEntry,
          dependenciesCache,
          shallowDependencies,
        };

        packagerServer.setHMRFileChangeListener(filename => {
          if (!client) {
            return Promise.resolve();
          }

          return packagerServer.getShallowDependencies(filename)
            .then(deps => {
              // if the file dependencies have change we need to invalidate the
              // dependencies caches because the list of files we need to send
              // to the client may have changed
              if (arrayEquals(deps, client.shallowDependencies[filename])) {
                return Promise.resolve();
              }
              return getDependencies(client.platform, client.bundleEntry)
                .then(({dependenciesCache, shallowDependencies}) => {
                  // invalidate caches
                  client.dependenciesCache = dependenciesCache;
                  client.shallowDependencies = shallowDependencies;
                });
            })
            .then(() => {
              // make sure the file was modified is part of the bundle
              if (!client.shallowDependencies[filename]) {
                return;
              }

              return packagerServer.buildBundleForHMR({
                platform: client.platform,
                entryFile: filename,
              })
              .then(bundle => client.ws.send(bundle));
            });
        });

        client.ws.on('error', e => {
          console.error('[Hot Module Replacement] Unexpected error', e);
          disconnect();
        });

        client.ws.on('close', () => disconnect());
      })
    .done();
  });
}

function arrayEquals(arrayA, arrayB) {
  arrayA = arrayA || [];
  arrayB = arrayB || [];
  return (
    arrayA.length === arrayB.length &&
    arrayA.every((element, index) => {
      return element === arrayB[index];
    })
  );
}

module.exports = attachHMRServer;