(function( $ ){
    
/**
 * A tilesource implementation for OpenStreetMap. Adopted from Rainer Simon
 * project http://github.com/rsimon/seajax-utils.
 *
 * Note 1. Zoomlevels. Deep Zoom and OSM define zoom levels differently. In  Deep 
 * Zoom, level 0 equals an image of 1x1 pixels. In OSM, level 0 equals an image of
 * 256x256 levels (see http://gasi.ch/blog/inside-deep-zoom-2). I.e. there is a 
 * difference of log2(256)=8 levels.
 *
 * Note 2. Image dimension. According to the OSM Wiki 
 * (http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames#Zoom_levels)
 * the highest Mapnik zoom level has 256.144x256.144 tiles, with a 256x256
 * pixel size. I.e. the Deep Zoom image dimension is 65.572.864x65.572.864
 * pixels.
 *
 * @class
 * @extends OpenSeadragon.TileSource
 * @param {Number|Object} width - the pixel width of the image or the idiomatic
 *      options object which is used instead of positional arguments.
 * @param {Number} height
 * @param {Number} tileSize
 * @param {Number} tileOverlap
 * @param {String} tilesUrl
 */ 
$.OsmTileSource = function( width, height, tileSize, tileOverlap, tilesUrl ) {
    var options;

    if( $.isPlainObject( width ) ){
        options = width;
    }else{
        options = {
            width: arguments[0],
            height: arguments[1],
            tileSize: arguments[2],
            tileOverlap: arguments[3],
            tilesUrl: arguments[4]
        };
    }
    //apply default setting for standard public OpenStreatMaps service
    //but allow them to be specified so fliks can host there own instance
    //or apply against other services supportting the same standard
    if( !options.width || !options.height ){
        options.width = 65572864;
        options.height = 65572864;
    }
    if( !options.tileSize ){
        options.tileSize = 256;
        options.tileOverlap = 0;
    }
    if( !options.tilesUrl ){
        options.tilesUrl = "http://tile.openstreetmap.org/";
    }
    options.minLevel = 8;
    
    $.TileSource.apply( this, [ options ] );

};

$.extend( $.OsmTileSource.prototype, $.TileSource.prototype, {


    /**
     * Determine if the data and/or url imply the image service is supported by
     * this tile source.
     * @function
     * @name OpenSeadragon.OsmTileSource.prototype.supports
     * @param {Object|Array} data
     * @param {String} optional - url
     */
    supports: function( data, url ){
        return ( 
            data.type && 
            "openstreetmaps" == data.type
        );
    },

    /**
     * 
     * @function
     * @name OpenSeadragon.OsmTileSource.prototype.configure
     * @param {Object} data - the raw configuration
     * @param {String} url - the url the data was retreived from if any.
     * @return {Object} options - A dictionary of keyword arguments sufficient 
     *      to configure this tile sources constructor.
     */
    configure: function( data, url ){
        return data;
    },


    /**
     * @function
     * @name OpenSeadragon.OsmTileSource.prototype.getTileUrl
     * @param {Number} level
     * @param {Number} x
     * @param {Number} y
     */
    getTileUrl: function( level, x, y ) {
        return this.tilesUrl + (level - 8) + "/" + x + "/" + y + ".png";
    }
});


}( OpenSeadragon ));