# Source: src/ol/source/stamensource.js

    goog.provide('ol.source.Stamen');

    goog.require('goog.asserts');
    goog.require('ol');
    goog.require('ol.Attribution');
    goog.require('ol.source.OSM');
    goog.require('ol.source.XYZ');

    /**
     * @type {Object.<string, {extension: string, opaque: boolean}>}
     */
    ol.source.StamenLayerConfig = {
      'terrain': {
        extension: 'jpg',
        opaque: true
      },
      'terrain-background': {
        extension: 'jpg',
        opaque: true
      },
      'terrain-labels': {
        extension: 'png',
        opaque: false
      },
      'terrain-lines': {
        extension: 'png',
        opaque: false
      },
      'toner-background': {
        extension: 'png',
        opaque: true
      },
      'toner': {
        extension: 'png',
        opaque: true
      },
      'toner-hybrid': {
        extension: 'png',
        opaque: false
      },
      'toner-labels': {
        extension: 'png',
        opaque: false
      },
      'toner-lines': {
        extension: 'png',
        opaque: false
      },
      'toner-lite': {
        extension: 'png',
        opaque: true
      },
      'watercolor': {
        extension: 'jpg',
        opaque: true
      }
    };

    /**
     * @type {Object.<string, {minZoom: number, maxZoom: number}>}
     */
    ol.source.StamenProviderConfig = {
      'terrain': {
        minZoom: 4,
        maxZoom: 18
      },
      'toner': {
        minZoom: 0,
        maxZoom: 20
      },
      'watercolor': {
        minZoom: 3,
        maxZoom: 16
      }
    };

    /**
     * @classdesc
     * Layer source for the Stamen tile server.
     *
     * @constructor
     * @extends {ol.source.XYZ}
     * @param {olx.source.StamenOptions} options Stamen options.
     * @todo api
     */
    ol.source.Stamen = function(options) {

      var i = options.layer.indexOf('-');
      var provider = i == -1 ? options.layer : options.layer.slice(0, i);
      goog.asserts.assert(provider in ol.source.StamenProviderConfig);
      var providerConfig = ol.source.StamenProviderConfig[provider];

      goog.asserts.assert(options.layer in ol.source.StamenLayerConfig);
      var layerConfig = ol.source.StamenLayerConfig[options.layer];

      var protocol = ol.IS_HTTPS ? 'https:' : 'http:';
      var url = goog.isDef(options.url) ? options.url :
          protocol + '//{a-d}.tile.stamen.com/' + options.layer + '/{z}/{x}/{y}.' +
          layerConfig.extension;

      goog.base(this, {
        attributions: ol.source.Stamen.ATTRIBUTIONS,
        crossOrigin: 'anonymous',
        maxZoom: providerConfig.maxZoom,
        // FIXME uncomment the following when tilegrid supports minZoom
        //minZoom: providerConfig.minZoom,
        opaque: layerConfig.opaque,
        tileLoadFunction: options.tileLoadFunction,
        url: url
      });

    };
    goog.inherits(ol.source.Stamen, ol.source.XYZ);

    /**
     * @const
     * @type {Array.<ol.Attribution>}
     */
    ol.source.Stamen.ATTRIBUTIONS = [
      new ol.Attribution({
        html: 'Map tiles by <a href="http://stamen.com/">Stamen Design</a>, ' +
            'under <a href="http://creativecommons.org/licenses/by/3.0/">CC BY' +
            ' 3.0</a>.'
      }),
      ol.source.OSM.DATA_ATTRIBUTION
    ];