/* Copyright (c) 2006-2011 by OpenLayers Contributors (see authors.txt for 
 * full list of contributors). Published under the Clear BSD license.  
 * See http://svn.openlayers.org/trunk/openlayers/license.txt for the
 * full text of the license. */


/**
 * @requires OpenLayers/Layer/Grid.js
 * @requires OpenLayers/Tile/Image.js
 */

/**
 * Class: OpenLayers.Layer.WMS
 * Instances of OpenLayers.Layer.WMS are used to display data from OGC Web
 *     Mapping Services. Create a new WMS layer with the <OpenLayers.Layer.WMS>
 *     constructor.
 * 
 * Inherits from:
 *  - <OpenLayers.Layer.Grid>
 */
OpenLayers.Layer.WMS = OpenLayers.Class(OpenLayers.Layer.Grid, {

    /**
     * Constant: DEFAULT_PARAMS
     * {Object} Hashtable of default parameter key/value pairs 
     */
    DEFAULT_PARAMS: { service: "WMS",
                      version: "1.1.1",
                      request: "GetMap",
                      styles: "",
                      format: "image/jpeg"
                     },
    
    /**
     * Property: reproject
     * *Deprecated*. See http://trac.openlayers.org/wiki/SphericalMercator
     * for information on the replacement for this functionality. 
     * {Boolean} Try to reproject this layer if its coordinate reference system
     *           is different than that of the base layer.  Default is false.  
     *           Set this in the layer options.  Should be set to false in 
     *           most cases.
     */
    reproject: false,
 
    /**
     * APIProperty: isBaseLayer
     * {Boolean} Default is true for WMS layer
     */
    isBaseLayer: true,
    
    /**
     * APIProperty: encodeBBOX
     * {Boolean} Should the BBOX commas be encoded? The WMS spec says 'no', 
     * but some services want it that way. Default false.
     */
    encodeBBOX: false,

    /** 值默认为false，如此设置为true,当设置类参数TRANSPARENT="TRUE"时不会自动转换图片格式，而且不能修改是否是基础层。
    * APIProperty: noMagic 
    * {Boolean} If true, the image format will not be automagically switched 
    *     from image/jpeg to image/png or image/gif when using 
    *     TRANSPARENT=TRUE. Also isBaseLayer will not changed by the  
    *     constructor. Default false. 
    */ 
    noMagic: false,
    
    /**
     * Property: yx
     * {Object} Keys in this object are EPSG codes for which the axis order
     *     is to be reversed (yx instead of xy, LatLon instead of LonLat), with
     *     true as value. This is only relevant for WMS versions >= 1.3.0.
     */
    yx: {'EPSG:4326': true},
    
    /**
     * Constructor: OpenLayers.Layer.WMS
     * Create a new WMS layer object
     *
     * Examples:
     *
     * The code below creates a simple WMS layer using the image/jpeg format.
     * (code)
     * var wms = new OpenLayers.Layer.WMS("NASA Global Mosaic",
     *                                    "http://wms.jpl.nasa.gov/wms.cgi", 
     *                                    {layers: "modis,global_mosaic"});
     * (end)
     * Note the 3rd argument (params). Properties added to this object will be
     * added to the WMS GetMap requests used for this layer's tiles. The only
     * mandatory parameter is "layers". Other common WMS params include
     * "transparent", "styles" and "format". Note that the "srs" param will
     * always be ignored. Instead, it will be derived from the baseLayer's or
     * map's projection.
     *
     * The code below creates a transparent WMS layer with additional options.
     * (code)
     * var wms = new OpenLayers.Layer.WMS("NASA Global Mosaic",
     *                                    "http://wms.jpl.nasa.gov/wms.cgi", 
     *                                    {
     *                                        layers: "modis,global_mosaic",
     *                                        transparent: true
     *                                    }, {
     *                                        opacity: 0.5,
     *                                        singleTile: true
     *                                    });
     * (end)
     * Note that by default, a WMS layer is configured as baseLayer. Setting
     * the "transparent" param to true will apply some magic (see <noMagic>).
     * The default image format changes from image/jpeg to image/png, and the
     * layer is not configured as baseLayer.
     *
     * Parameters:
     * name - {String} A name for the layer
     * url - {String} Base url for the WMS
     *                (e.g. http://wms.jpl.nasa.gov/wms.cgi)
     * params - {Object} An object with key/value pairs representing the
     *                   GetMap query string parameters and parameter values.
     * options - {Object} Hashtable of extra options to tag onto the layer.
     *     These options include all properties listed above, plus the ones
     *     inherited from superclasses.
     */
    initialize: function(name, url, params, options) {
        var newArguments = [];
        //uppercase params
        params = OpenLayers.Util.upperCaseObject(params);
        if (parseFloat(params.VERSION) >= 1.3 && !params.EXCEPTIONS) {
            params.EXCEPTIONS = "INIMAGE"; //OGC-WMS 的EXCEPTIONS参数
        } 
        newArguments.push(name, url, params, options);
        OpenLayers.Layer.Grid.prototype.initialize.apply(this, newArguments);
        OpenLayers.Util.applyDefaults(
                       this.params, 
                       OpenLayers.Util.upperCaseObject(this.DEFAULT_PARAMS)
                       );//将WMS的默认参数大写化后传给WMS对象


        //layer is transparent        
        if (!this.noMagic && this.params.TRANSPARENT && 
            this.params.TRANSPARENT.toString().toLowerCase() == "true") {
            
            // unless explicitly set in options, make layer an overlay
            if ( (options == null) || (!options.isBaseLayer) ) {
                this.isBaseLayer = false;
            } 
            
            // jpegs can never be transparent, so intelligently switch the 
            //  format, depending on the browser's capabilities
            if (this.params.FORMAT == "image/jpeg") {
                this.params.FORMAT = OpenLayers.Util.alphaHack() ? "image/gif"
                                                                 : "image/png";
            }
        }

    },    

    /**
     * Method: destroy
     * Destroy this layer
     */
    destroy: function() {
        // for now, nothing special to do here. 
        OpenLayers.Layer.Grid.prototype.destroy.apply(this, arguments);  
    },

    
    /**
     * Method: clone
     * Create a clone of this layer
     *
     * Returns:
     * {<OpenLayers.Layer.WMS>} An exact clone of this layer
     */
    clone: function (obj) {
        
        if (obj == null) {
            obj = new OpenLayers.Layer.WMS(this.name,
                                           this.url,
                                           this.params,
                                           this.getOptions());
        }

        //get all additions from superclasses
        obj = OpenLayers.Layer.Grid.prototype.clone.apply(this, [obj]);

        // copy/set any non-init, non-simple values here

        return obj;
    },    
    
    /**
     * APIMethod: reverseAxisOrder
     * Returns true if the axis order is reversed for the WMS version and
     * projection of the layer.
     * 
     * Returns:
     * {Boolean} true if the axis order is reversed, false otherwise.
     */
    reverseAxisOrder: function() {
        return (parseFloat(this.params.VERSION) >= 1.3 && 
            !!this.yx[this.map.getProjectionObject().getCode()]);
    },
    
    /**
     * Method: getURL
     * Return a GetMap query string for this layer
     *
     * Parameters:
     * bounds - {<OpenLayers.Bounds>} A bounds representing the bbox for the
     *                                request.
     *
     * Returns:
     * {String} A string with the layer's url and parameters and also the
     *          passed-in bounds and appropriate tile size specified as 
     *          parameters.
     */
    getURL: function (bounds) {
        bounds = this.adjustBounds(bounds);
        
        var imageSize = this.getImageSize();
        var newParams = {};
        // WMS 1.3 introduced axis order
        var reverseAxisOrder = this.reverseAxisOrder();
        newParams.BBOX = this.encodeBBOX ?
            bounds.toBBOX(null, reverseAxisOrder) :
            bounds.toArray(reverseAxisOrder);
        newParams.WIDTH = imageSize.w;
        newParams.HEIGHT = imageSize.h;
        var requestString = this.getFullRequestString(newParams);
        return requestString;
    },

    /**
     * APIMethod: mergeNewParams
     * Catch changeParams and uppercase the new params to be merged in
     *     before calling changeParams on the super class.
     * 
     *     Once params have been changed, the tiles will be reloaded with
     *     the new parameters.
     * 
     * Parameters:
     * newParams - {Object} Hashtable of new params to use
     */
    mergeNewParams:function(newParams) {
        var upperParams = OpenLayers.Util.upperCaseObject(newParams);
        var newArguments = [upperParams];
        return OpenLayers.Layer.Grid.prototype.mergeNewParams.apply(this, 
                                                             newArguments);
    },

    /** 
     * APIMethod: getFullRequestString
     * Combine the layer's url with its params and these newParams. 
     *   
     *     Add the SRS parameter from projection -- this is probably
     *     more eloquently done via a setProjection() method, but this 
     *     works for now and always.
     *
     * Parameters:
     * newParams - {Object}
     * altUrl - {String} Use this as the url instead of the layer's url
     * 
     * Returns:
     * {String} 
     */
    getFullRequestString:function(newParams, altUrl) {
        var mapProjection = this.map.getProjectionObject();
        var projectionCode = this.projection && this.projection.equals(mapProjection) ?
            this.projection.getCode() :
            mapProjection.getCode();
        var value = (projectionCode == "none") ? null : projectionCode;
        if (parseFloat(this.params.VERSION) >= 1.3) {
            this.params.CRS = value;
        } else {
            this.params.SRS = value;
        }
        
        if (typeof this.params.TRANSPARENT == "boolean") {
            newParams.TRANSPARENT = this.params.TRANSPARENT ? "TRUE" : "FALSE";
        }

        return OpenLayers.Layer.Grid.prototype.getFullRequestString.apply(
                                                    this, arguments);
    },

    CLASS_NAME: "OpenLayers.Layer.WMS"
});