<!--
@license
Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
Code distributed by Google as part of the polymer project is also
subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
-->

<link rel="import" href="../polymer/polymer.html">
<link rel="import" href="../iron-a11y-keys-behavior/iron-a11y-keys-behavior.html">
<link rel="import" href="iron-overlay-backdrop.html">

<script>

  /**
   * @struct
   * @constructor
   * @private
   */
  Polymer.IronOverlayManagerClass = function() {
    /**
     * Used to keep track of the opened overlays.
     * @private {Array<Element>}
     */
    this._overlays = [];

    /**
     * iframes have a default z-index of 100,
     * so this default should be at least that.
     * @private {number}
     */
    this._minimumZ = 101;

    /**
     * Memoized backdrop element.
     * @private {Element|null}
     */
    this._backdropElement = null;

    // Enable document-wide tap recognizer.
    Polymer.Gestures.add(document, 'tap', null);
    // Need to have useCapture=true, Polymer.Gestures doesn't offer that.
    document.addEventListener('tap', this._onCaptureClick.bind(this), true);
    document.addEventListener('focus', this._onCaptureFocus.bind(this), true);
    document.addEventListener('keydown', this._onCaptureKeyDown.bind(this), true);
  };

  Polymer.IronOverlayManagerClass.prototype = {

    constructor: Polymer.IronOverlayManagerClass,

    /**
     * The shared backdrop element.
     * @type {!Element} backdropElement
     */
    get backdropElement() {
      if (!this._backdropElement) {
        this._backdropElement = document.createElement('iron-overlay-backdrop');
      }
      return this._backdropElement;
    },

    /**
     * The deepest active element.
     * @type {!Element} activeElement the active element
     */
    get deepActiveElement() {
      // document.activeElement can be null
      // https://developer.mozilla.org/en-US/docs/Web/API/Document/activeElement
      // In case of null, default it to document.body.
      var active = document.activeElement || document.body;
      while (active.root && Polymer.dom(active.root).activeElement) {
        active = Polymer.dom(active.root).activeElement;
      }
      return active;
    },

    /**
     * Brings the overlay at the specified index to the front.
     * @param {number} i
     * @private
     */
    _bringOverlayAtIndexToFront: function(i) {
      var overlay = this._overlays[i];
      if (!overlay) {
        return;
      }
      var lastI = this._overlays.length - 1;
      var currentOverlay = this._overlays[lastI];
      // Ensure always-on-top overlay stays on top.
      if (currentOverlay && this._shouldBeBehindOverlay(overlay, currentOverlay)) {
        lastI--;
      }
      // If already the top element, return.
      if (i >= lastI) {
        return;
      }
      // Update z-index to be on top.
      var minimumZ = Math.max(this.currentOverlayZ(), this._minimumZ);
      if (this._getZ(overlay) <= minimumZ) {
        this._applyOverlayZ(overlay, minimumZ);
      }

      // Shift other overlays behind the new on top.
      while (i < lastI) {
        this._overlays[i] = this._overlays[i + 1];
        i++;
      }
      this._overlays[lastI] = overlay;
    },

    /**
     * Adds the overlay and updates its z-index if it's opened, or removes it if it's closed.
     * Also updates the backdrop z-index.
     * @param {!Element} overlay
     */
    addOrRemoveOverlay: function(overlay) {
      if (overlay.opened) {
        this.addOverlay(overlay);
      } else {
        this.removeOverlay(overlay);
      }
    },

    /**
     * Tracks overlays for z-index and focus management.
     * Ensures the last added overlay with always-on-top remains on top.
     * @param {!Element} overlay
     */
    addOverlay: function(overlay) {
      var i = this._overlays.indexOf(overlay);
      if (i >= 0) {
        this._bringOverlayAtIndexToFront(i);
        this.trackBackdrop();
        return;
      }
      var insertionIndex = this._overlays.length;
      var currentOverlay = this._overlays[insertionIndex - 1];
      var minimumZ = Math.max(this._getZ(currentOverlay), this._minimumZ);
      var newZ = this._getZ(overlay);

      // Ensure always-on-top overlay stays on top.
      if (currentOverlay && this._shouldBeBehindOverlay(overlay, currentOverlay)) {
        // This bumps the z-index of +2.
        this._applyOverlayZ(currentOverlay, minimumZ);
        insertionIndex--;
        // Update minimumZ to match previous overlay's z-index.
        var previousOverlay = this._overlays[insertionIndex - 1];
        minimumZ = Math.max(this._getZ(previousOverlay), this._minimumZ);
      }

      // Update z-index and insert overlay.
      if (newZ <= minimumZ) {
        this._applyOverlayZ(overlay, minimumZ);
      }
      this._overlays.splice(insertionIndex, 0, overlay);

      // Get focused node.
      var element = this.deepActiveElement;
      overlay.restoreFocusNode = this._overlayParent(element) ? null : element;
      this.trackBackdrop();
    },

    /**
     * @param {!Element} overlay
     */
    removeOverlay: function(overlay) {
      var i = this._overlays.indexOf(overlay);
      if (i === -1) {
        return;
      }
      this._overlays.splice(i, 1);

      var node = overlay.restoreFocusOnClose ? overlay.restoreFocusNode : null;
      overlay.restoreFocusNode = null;
      // Focus back only if still contained in document.body
      if (node && Polymer.dom(document.body).deepContains(node)) {
        node.focus();
      }
      this.trackBackdrop();
    },

    /**
     * Returns the current overlay.
     * @return {Element|undefined}
     */
    currentOverlay: function() {
      var i = this._overlays.length - 1;
      return this._overlays[i];
    },

    /**
     * Returns the current overlay z-index.
     * @return {number}
     */
    currentOverlayZ: function() {
      return this._getZ(this.currentOverlay());
    },

    /**
     * Ensures that the minimum z-index of new overlays is at least `minimumZ`.
     * This does not effect the z-index of any existing overlays.
     * @param {number} minimumZ
     */
    ensureMinimumZ: function(minimumZ) {
      this._minimumZ = Math.max(this._minimumZ, minimumZ);
    },

    focusOverlay: function() {
      var current = /** @type {?} */ (this.currentOverlay());
      // We have to be careful to focus the next overlay _after_ any current
      // transitions are complete (due to the state being toggled prior to the
      // transition). Otherwise, we risk infinite recursion when a transitioning
      // (closed) overlay becomes the current overlay.
      //
      // NOTE: We make the assumption that any overlay that completes a transition
      // will call into focusOverlay to kick the process back off. Currently:
      // transitionend -> _applyFocus -> focusOverlay.
      if (current && !current.transitioning) {
        current._applyFocus();
      }
    },

    /**
     * Updates the backdrop z-index.
     */
    trackBackdrop: function() {
      var overlay = this._overlayWithBackdrop();
      // Avoid creating the backdrop if there is no overlay with backdrop.
      if (!overlay && !this._backdropElement) {
        return;
      }
      this.backdropElement.style.zIndex = this._getZ(overlay) - 1;
      this.backdropElement.opened = !!overlay;
    },

    /**
     * @return {Array<Element>}
     */
    getBackdrops: function() {
      var backdrops = [];
      for (var i = 0; i < this._overlays.length; i++) {
        if (this._overlays[i].withBackdrop) {
          backdrops.push(this._overlays[i]);
        }
      }
      return backdrops;
    },

    /**
     * Returns the z-index for the backdrop.
     * @return {number}
     */
    backdropZ: function() {
      return this._getZ(this._overlayWithBackdrop()) - 1;
    },

    /**
     * Returns the first opened overlay that has a backdrop.
     * @return {Element|undefined}
     * @private
     */
    _overlayWithBackdrop: function() {
      for (var i = 0; i < this._overlays.length; i++) {
        if (this._overlays[i].withBackdrop) {
          return this._overlays[i];
        }
      }
    },

    /**
     * Calculates the minimum z-index for the overlay.
     * @param {Element=} overlay
     * @private
     */
    _getZ: function(overlay) {
      var z = this._minimumZ;
      if (overlay) {
        var z1 = Number(overlay.style.zIndex || window.getComputedStyle(overlay).zIndex);
        // Check if is a number
        // Number.isNaN not supported in IE 10+
        if (z1 === z1) {
          z = z1;
        }
      }
      return z;
    },

    /**
     * @param {!Element} element
     * @param {number|string} z
     * @private
     */
    _setZ: function(element, z) {
      element.style.zIndex = z;
    },

    /**
     * @param {!Element} overlay
     * @param {number} aboveZ
     * @private
     */
    _applyOverlayZ: function(overlay, aboveZ) {
      this._setZ(overlay, aboveZ + 2);
    },

    /**
     * Returns the overlay containing the provided node. If the node is an overlay,
     * it returns the node.
     * @param {Element=} node
     * @return {Element|undefined}
     * @private
     */
    _overlayParent: function(node) {
      while (node && node !== document.body) {
        // Check if it is an overlay.
        if (node._manager === this) {
          return node;
        }
        // Use logical parentNode, or native ShadowRoot host.
        node = Polymer.dom(node).parentNode || node.host;
      }
    },

    /**
     * Returns the deepest overlay in the path.
     * @param {Array<Element>=} path
     * @return {Element|undefined}
     * @suppress {missingProperties}
     * @private
     */
    _overlayInPath: function(path) {
      path = path || [];
      for (var i = 0; i < path.length; i++) {
        if (path[i]._manager === this) {
          return path[i];
        }
      }
    },

    /**
     * Ensures the click event is delegated to the right overlay.
     * @param {!Event} event
     * @private
     */
    _onCaptureClick: function(event) {
      var overlay = /** @type {?} */ (this.currentOverlay());
      // Check if clicked outside of top overlay.
      if (overlay && this._overlayInPath(Polymer.dom(event).path) !== overlay) {
        overlay._onCaptureClick(event);
      }
    },

    /**
     * Ensures the focus event is delegated to the right overlay.
     * @param {!Event} event
     * @private
     */
    _onCaptureFocus: function(event) {
      var overlay = /** @type {?} */ (this.currentOverlay());
      if (overlay) {
        overlay._onCaptureFocus(event);
      }
    },

    /**
     * Ensures TAB and ESC keyboard events are delegated to the right overlay.
     * @param {!Event} event
     * @private
     */
    _onCaptureKeyDown: function(event) {
      var overlay = /** @type {?} */ (this.currentOverlay());
      if (overlay) {
        if (Polymer.IronA11yKeysBehavior.keyboardEventMatchesKeys(event, 'esc')) {
          overlay._onCaptureEsc(event);
        } else if (Polymer.IronA11yKeysBehavior.keyboardEventMatchesKeys(event, 'tab')) {
          overlay._onCaptureTab(event);
        }
      }
    },

    /**
     * Returns if the overlay1 should be behind overlay2.
     * @param {!Element} overlay1
     * @param {!Element} overlay2
     * @return {boolean}
     * @suppress {missingProperties}
     * @private
     */
    _shouldBeBehindOverlay: function(overlay1, overlay2) {
      return !overlay1.alwaysOnTop && overlay2.alwaysOnTop;
    }
  };

  Polymer.IronOverlayManager = new Polymer.IronOverlayManagerClass();
</script>