import defined from "./defined.js";

let _supportsFullscreen;
const _names = {
  requestFullscreen: undefined,
  exitFullscreen: undefined,
  fullscreenEnabled: undefined,
  fullscreenElement: undefined,
  fullscreenchange: undefined,
  fullscreenerror: undefined,
};

/**
 * Browser-independent functions for working with the standard fullscreen API.
 *
 * @namespace Fullscreen
 *
 * @see {@link http://dvcs.w3.org/hg/fullscreen/raw-file/tip/Overview.html|W3C Fullscreen Living Specification}
 */
const Fullscreen = {};

Object.defineProperties(Fullscreen, {
  /**
   * The element that is currently fullscreen, if any.  To simply check if the
   * browser is in fullscreen mode or not, use {@link Fullscreen#fullscreen}.
   * @memberof Fullscreen
   * @type {Object}
   * @readonly
   */
  element: {
    get: function () {
      if (!Fullscreen.supportsFullscreen()) {
        return undefined;
      }

      return document[_names.fullscreenElement];
    },
  },

  /**
   * The name of the event on the document that is fired when fullscreen is
   * entered or exited.  This event name is intended for use with addEventListener.
   * In your event handler, to determine if the browser is in fullscreen mode or not,
   * use {@link Fullscreen#fullscreen}.
   * @memberof Fullscreen
   * @type {String}
   * @readonly
   */
  changeEventName: {
    get: function () {
      if (!Fullscreen.supportsFullscreen()) {
        return undefined;
      }

      return _names.fullscreenchange;
    },
  },

  /**
   * The name of the event that is fired when a fullscreen error
   * occurs.  This event name is intended for use with addEventListener.
   * @memberof Fullscreen
   * @type {String}
   * @readonly
   */
  errorEventName: {
    get: function () {
      if (!Fullscreen.supportsFullscreen()) {
        return undefined;
      }

      return _names.fullscreenerror;
    },
  },

  /**
   * Determine whether the browser will allow an element to be made fullscreen, or not.
   * For example, by default, iframes cannot go fullscreen unless the containing page
   * adds an "allowfullscreen" attribute (or prefixed equivalent).
   * @memberof Fullscreen
   * @type {Boolean}
   * @readonly
   */
  enabled: {
    get: function () {
      if (!Fullscreen.supportsFullscreen()) {
        return undefined;
      }

      return document[_names.fullscreenEnabled];
    },
  },

  /**
   * Determines if the browser is currently in fullscreen mode.
   * @memberof Fullscreen
   * @type {Boolean}
   * @readonly
   */
  fullscreen: {
    get: function () {
      if (!Fullscreen.supportsFullscreen()) {
        return undefined;
      }

      return Fullscreen.element !== null;
    },
  },
});

/**
 * Detects whether the browser supports the standard fullscreen API.
 *
 * @returns {Boolean} <code>true</code> if the browser supports the standard fullscreen API,
 * <code>false</code> otherwise.
 */
Fullscreen.supportsFullscreen = function () {
  if (defined(_supportsFullscreen)) {
    return _supportsFullscreen;
  }

  _supportsFullscreen = false;

  const body = document.body;
  if (typeof body.requestFullscreen === "function") {
    // go with the unprefixed, standard set of names
    _names.requestFullscreen = "requestFullscreen";
    _names.exitFullscreen = "exitFullscreen";
    _names.fullscreenEnabled = "fullscreenEnabled";
    _names.fullscreenElement = "fullscreenElement";
    _names.fullscreenchange = "fullscreenchange";
    _names.fullscreenerror = "fullscreenerror";
    _supportsFullscreen = true;
    return _supportsFullscreen;
  }

  //check for the correct combination of prefix plus the various names that browsers use
  const prefixes = ["webkit", "moz", "o", "ms", "khtml"];
  let name;
  for (let i = 0, len = prefixes.length; i < len; ++i) {
    const prefix = prefixes[i];

    // casing of Fullscreen differs across browsers
    name = `${prefix}RequestFullscreen`;
    if (typeof body[name] === "function") {
      _names.requestFullscreen = name;
      _supportsFullscreen = true;
    } else {
      name = `${prefix}RequestFullScreen`;
      if (typeof body[name] === "function") {
        _names.requestFullscreen = name;
        _supportsFullscreen = true;
      }
    }

    // disagreement about whether it's "exit" as per spec, or "cancel"
    name = `${prefix}ExitFullscreen`;
    if (typeof document[name] === "function") {
      _names.exitFullscreen = name;
    } else {
      name = `${prefix}CancelFullScreen`;
      if (typeof document[name] === "function") {
        _names.exitFullscreen = name;
      }
    }

    // casing of Fullscreen differs across browsers
    name = `${prefix}FullscreenEnabled`;
    if (document[name] !== undefined) {
      _names.fullscreenEnabled = name;
    } else {
      name = `${prefix}FullScreenEnabled`;
      if (document[name] !== undefined) {
        _names.fullscreenEnabled = name;
      }
    }

    // casing of Fullscreen differs across browsers
    name = `${prefix}FullscreenElement`;
    if (document[name] !== undefined) {
      _names.fullscreenElement = name;
    } else {
      name = `${prefix}FullScreenElement`;
      if (document[name] !== undefined) {
        _names.fullscreenElement = name;
      }
    }

    // thankfully, event names are all lowercase per spec
    name = `${prefix}fullscreenchange`;
    // event names do not have 'on' in the front, but the property on the document does
    if (document[`on${name}`] !== undefined) {
      //except on IE
      if (prefix === "ms") {
        name = "MSFullscreenChange";
      }
      _names.fullscreenchange = name;
    }

    name = `${prefix}fullscreenerror`;
    if (document[`on${name}`] !== undefined) {
      //except on IE
      if (prefix === "ms") {
        name = "MSFullscreenError";
      }
      _names.fullscreenerror = name;
    }
  }

  return _supportsFullscreen;
};

/**
 * Asynchronously requests the browser to enter fullscreen mode on the given element.
 * If fullscreen mode is not supported by the browser, does nothing.
 *
 * @param {Object} element The HTML element which will be placed into fullscreen mode.
 * @param {Object} [vrDevice] The HMDVRDevice device.
 *
 * @example
 * // Put the entire page into fullscreen.
 * Cesium.Fullscreen.requestFullscreen(document.body)
 *
 * // Place only the Cesium canvas into fullscreen.
 * Cesium.Fullscreen.requestFullscreen(scene.canvas)
 */
Fullscreen.requestFullscreen = function (element, vrDevice) {
  if (!Fullscreen.supportsFullscreen()) {
    return;
  }

  element[_names.requestFullscreen]({ vrDisplay: vrDevice });
};

/**
 * Asynchronously exits fullscreen mode.  If the browser is not currently
 * in fullscreen, or if fullscreen mode is not supported by the browser, does nothing.
 */
Fullscreen.exitFullscreen = function () {
  if (!Fullscreen.supportsFullscreen()) {
    return;
  }

  document[_names.exitFullscreen]();
};

//For unit tests
Fullscreen._names = _names;
export default Fullscreen;