text: /* @flow */
  
  import { AppState } from 'react-native';
  import type { Dispatch } from 'redux';
  
  import {
      APP_WILL_MOUNT,
      APP_WILL_UNMOUNT
  } from '../app';
  import { MiddlewareRegistry } from '../base/redux';
  
  import {
      _setAppStateListener,
      _setBackgroundVideoMuted,
      appStateChanged
  } from './actions';
  import {
      _SET_APP_STATE_LISTENER,
      APP_STATE_CHANGED
  } from './actionTypes';
  
  /**
   * Middleware that captures App lifetime actions and subscribes to application
   * state changes. When the application state changes it will fire the action
   * required to mute or unmute the local video in case the application goes to
   * the background or comes back from it.
   *
   * @param {Store} store - Redux store.
   * @returns {Function}
   * @see {@link https://facebook.github.io/react-native/docs/appstate.html}
   */
  MiddlewareRegistry.register(store => next => action => {
      switch (action.type) {
      case _SET_APP_STATE_LISTENER: {
          // Remove the current/old AppState listener.
          const { appStateListener } = store.getState()['features/background'];
  
          if (appStateListener) {
              AppState.removeEventListener('change', appStateListener);
          }
  
          // Add the new AppState listener.
          if (action.listener) {
              AppState.addEventListener('change', action.listener);
          }
          break;
      }
  
      case APP_STATE_CHANGED:
          _appStateChanged(store.dispatch, action.appState);
          break;
  
      case APP_WILL_MOUNT:
          store.dispatch(
                  _setAppStateListener(
                          _onAppStateChange.bind(undefined, store.dispatch)));
          break;
  
      case APP_WILL_UNMOUNT:
          store.dispatch(_setAppStateListener(null));
          break;
      }
  
      return next(action);
  });
  
  /**
   * Handles app state changes. Dispatches the necessary Redux actions for the
   * local video to be muted when the app goes to the background, and to be
   * unmuted when the app comes back.
   *
   * @param {Dispatch} dispatch - Redux dispatch function.
   * @param {string} appState - The current app state.
   * @private
   * @returns {void}
   */
  function _appStateChanged(dispatch: Dispatch<*>, appState: string) {
      let muted;
  
      switch (appState) {
      case 'active':
          muted = false;
          break;
  
      case 'background':
          muted = true;
          break;
  
      case 'inactive':
      default:
          // XXX: We purposely don't handle the 'inactive' app state.
          return;
      }
  
      dispatch(_setBackgroundVideoMuted(muted));
  }
  
  /**
   * Called by React Native's AppState API to notify that the application state
   * has changed. Dispatches the change within the (associated) Redux store.
   *
   * @param {Dispatch} dispatch - Redux dispatch function.
   * @param {string} appState - The current application execution state.
   * @private
   * @returns {void}
   */
  function _onAppStateChange(dispatch: Dispatch<*>, appState: string) {
      dispatch(appStateChanged(appState));
  }
  