# Source: src/ol/control/logocontrol.js

    goog.provide('ol.control.Logo');

    goog.require('goog.dom');
    goog.require('goog.dom.TagName');
    goog.require('goog.object');
    goog.require('goog.style');
    goog.require('ol.control.Control');
    goog.require('ol.css');

    /**
     * @classdesc
     * Shows a logo for all the layer sources in the map that have a logo
     * associated with them, such as Bing. This control is part of a default map.
     * By default it will show in the bottom-left portion of the map, but it can
     * be styled by using a css selector for `.ol-logo`.
     *
     * @constructor
     * @extends {ol.control.Control}
     * @param {olx.control.LogoOptions=} opt_options Logo options.
     * @todo api
     */
    ol.control.Logo = function(opt_options) {

      var options = goog.isDef(opt_options) ? opt_options : {};

      /**
       * @private
       * @type {Element}
       */
      this.ulElement_ = goog.dom.createElement(goog.dom.TagName.UL);

      var className = goog.isDef(options.className) ? options.className : 'ol-logo';

      var element = goog.dom.createDom(goog.dom.TagName.DIV, {
        'class': className + ' ' + ol.css.CLASS_UNSELECTABLE
      }, this.ulElement_);

      goog.base(this, {
        element: element,
        target: options.target
      });

      /**
       * @private
       * @type {boolean}
       */
      this.renderedVisible_ = true;

      /**
       * @private
       * @type {Object.<string, Element>}
       */
      this.logoElements_ = {};

    };
    goog.inherits(ol.control.Logo, ol.control.Control);

    /**
     * @param {ol.MapEvent} mapEvent Map event.
     */
    ol.control.Logo.prototype.handleMapPostrender = function(mapEvent) {
      this.updateElement_(mapEvent.frameState);
    };

    /**
     * @param {?olx.FrameState} frameState Frame state.
     * @private
     */
    ol.control.Logo.prototype.updateElement_ = function(frameState) {

      if (goog.isNull(frameState)) {
        if (this.renderedVisible_) {
          goog.style.setElementShown(this.element, false);
          this.renderedVisible_ = false;
        }
        return;
      }

      var logo;
      var logos = frameState.logos;
      var logoElements = this.logoElements_;

      for (logo in logoElements) {
        if (!(logo in logos)) {
          goog.dom.removeNode(logoElements[logo]);
          delete logoElements[logo];
        }
      }

      var image, logoElement, logoKey;
      for (logoKey in logos) {
        if (!(logoKey in logoElements)) {
          image = new Image();
          image.src = logoKey;
          var logoValue = logos[logoKey];
          var child;
          if (logoValue === '') {
            child = image;
          } else {
            child = goog.dom.createDom(goog.dom.TagName.A, {
              'href': logoValue,
              'target': '_blank'
            });
            child.appendChild(image);
          }
          logoElement = goog.dom.createDom(goog.dom.TagName.LI, undefined, child);
          goog.dom.appendChild(this.ulElement_, logoElement);
          logoElements[logoKey] = logoElement;
        }
      }

      var renderVisible = !goog.object.isEmpty(logos);
      if (this.renderedVisible_ != renderVisible) {
        goog.style.setElementShown(this.element, renderVisible);
        this.renderedVisible_ = renderVisible;
      }

    };