/**
 * Namespace: Util.OSM
 */
OpenLayers.Util.OSM = {};

/**
 * Constant: MISSING_TILE_URL
 * {String} URL of image to display for missing tiles
 */
OpenLayers.Util.OSM.PP_MISSING_TILE_URL = "/manchester/images/pp_faint_404.png";

/**
 * Property: originalOnImageLoadError
 * {Function} Original onImageLoadError function.
 */
OpenLayers.Util.OSM.originalOnImageLoadError = OpenLayers.Util.onImageLoadError;

/**
 * Function: onImageLoadError
 */
OpenLayers.Util.onImageLoadError = function() {
	this.src = OpenLayers.Util.OSM.PP_MISSING_TILE_URL;
        //OpenLayers.Util.OSM.originalOnImageLoadError;
};

/**
 * @requires OpenLayers/Layer/TMS.js
 *
 * Class: OpenLayers.Layer.OSM
 *
 * Inherits from:
 *  - <OpenLayers.Layer.TMS>
 */
OpenLayers.Layer.OSM = OpenLayers.Class(OpenLayers.Layer.TMS, {
    /**
     * Constructor: OpenLayers.Layer.OSM
     *
     * Parameters:
     * name - {String}
     * url - {String}
     * options - {Object} Hashtable of extra options to tag onto the layer
     */
    initialize: function(name, url, options) {
        options = OpenLayers.Util.extend({
            attribution: "Data by <a href='http://openstreetmap.org/'>OpenStreetMap</a>",
 	    maxExtent: new OpenLayers.Bounds(-20037508.34,-20037508.34,20037508.34,20037508.34),
            maxResolution: 156543.0339,
            units: "m",
            projection: "EPSG:900913",          
            transitionEffect: "resize"
        }, options);
        var newArguments = [name, url, options];
        OpenLayers.Layer.TMS.prototype.initialize.apply(this, newArguments);
    },

/*
*/

    /**
     * Method: getUrl
     *
     * Parameters:
     * bounds - {<OpenLayers.Bounds>}
     *
     * 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) {
        var res = this.map.getResolution();
        var x = Math.round((bounds.left - this.maxExtent.left) / (res * this.tileSize.w));
        var y = Math.round((this.maxExtent.top - bounds.top) / (res * this.tileSize.h));
        var z = this.map.getZoom();
        var limit = Math.pow(2, z);

        if (y < 0 || y >= limit)
        {
            return OpenLayers.Util.OSM.PP_MISSING_TILE_URL;
        }
        else
        {
            x = ((x % limit) + limit) % limit;

            var url = this.url;
            var path = z + "/" + x + "/" + y + ".png";

            if (url instanceof Array)
            {
                url = this.selectUrl(path, url);
            }

            return url + path;
        }
    },

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


/**
 * Class: OpenLayers.Layer.OSM.Mapnik
 *
 * Inherits from:
 *  - <OpenLayers.Layer.OSM>
 */
OpenLayers.Layer.OSM.Mapnik = OpenLayers.Class(OpenLayers.Layer.OSM, {
    /**
     * Constructor: OpenLayers.Layer.OSM.Mapnik
     *
     * Parameters:
     * name - {String}
     * options - {Object} Hashtable of extra options to tag onto the layer
     */
    initialize: function(name, options) {
        var url = [
            "http://a.tile.openstreetmap.org/",
            "http://b.tile.openstreetmap.org/",
            "http://c.tile.openstreetmap.org/"
        ];
        options = OpenLayers.Util.extend({ numZoomLevels: 16 }, options);
        var newArguments = [name, url, options];
        OpenLayers.Layer.OSM.prototype.initialize.apply(this, newArguments);
    },

    CLASS_NAME: "OpenLayers.Layer.OSM.Mapnik"
});

/**
 * Class: OpenLayers.Layer.OSM.Oac
 *
 * Inherits from:
 *  - <OpenLayers.Layer.OSM>
 */
OpenLayers.Layer.OSM.Oac = OpenLayers.Class(OpenLayers.Layer.OSM, {
    /**
     * Constructor: OpenLayers.Layer.OSM.Oac
     *
     * Parameters:
     * name - {String}
     * options - {Object} Hashtable of extra options to tag onto the layer
     */
    initialize: function(name, url, options) {
        options = OpenLayers.Util.extend({ 
		numZoomLevels: 16, 
		isBaseLayer: false,
		attribution: "",
                opacity: 0.5,
		transitionEffect: null 
	}, options);
        var url = [ "http://splintdev.geog.ucl.ac.uk/Tiles/oac24/" ];        
        var newArguments = [name, url, options];
        OpenLayers.Layer.OSM.prototype.initialize.apply(this, newArguments);
    },

    CLASS_NAME: "OpenLayers.Layer.OSM.Oac"
});

OpenLayers.Layer.OSM.Manchester = OpenLayers.Class(OpenLayers.Layer.OSM, {
    initialize: function(name, url, options) {
        options = OpenLayers.Util.extend({ 
		numZoomLevels: 16, 
		isBaseLayer: false,
		attribution: "",
                opacity: 0.5,
		transitionEffect: null  
	}, options);
        var url = [ "/manchester/tiles/" ];
        var newArguments = [name, url, options];
        OpenLayers.Layer.OSM.prototype.initialize.apply(this, newArguments);
    },

    getURL: function (bounds) {
        var res = this.map.getResolution();
        var x = Math.round((bounds.left - this.maxExtent.left) / (res * this.tileSize.w));
        var y = Math.round((this.maxExtent.top - bounds.top) / (res * this.tileSize.h));
        var z = this.map.getZoom();
        var limit = Math.pow(2, z);

        if (y < 0 || y >= limit)
        {
            return "";
        }
        else
        {	
            var quadtree = "";
            for (var i = z; i > 0; i--)
            {
    		var mask = 1 << (i-1);
                var cell = 0;
                if ((x & mask) != 0) cell++;
                if ((y & mask) != 0) cell += 2;
    		quadtree += cell;    
            }    
            var url = this.url;
            var path = quadtree + ".png";

            if (url instanceof Array)
            {
                url = this.selectUrl(path, url);
            }
            return url + path;
        }
    },

    CLASS_NAME: "OpenLayers.Layer.OSM.Manchester"
});