(function( $ ){


/**
 * The TileSource contains the most basic implementation required to create a
 * smooth transition between layer in an image pyramid. It has only a single key 
 * interface that must be implemented to complete it key functionality: 
 * 'getTileUrl'.  It also has several optional interfaces that can be 
 * implemented if a new TileSource wishes to support configuration via a simple
 * object or array ('configure') and if the tile source supports or requires 
 * configuration via retreival of a document on the network ala AJAX or JSONP, 
 * ('getImageInfo').
 * <br/>
 * By default the image pyramid is split into N layers where the images longest
 * side in M (in pixels), where N is the smallest integer which satisfies 
 *      <strong>2^(N+1) >= M</strong>.
 * @class
 * @extends OpenSeadragon.EventHandler
 * @param {Number|Object|Array|String} width 
 *      If more than a single argument is supplied, the traditional use of 
 *      positional parameters is supplied and width is expected to be the width 
 *      source image at it's max resolution in pixels.  If a single argument is supplied and
 *      it is an Object or Array, the construction is assumed to occur through
 *      the extending classes implementation of 'configure'.  Finally if only a
 *      single argument is supplied and it is a String, the extending class is
 *      expected to implement 'getImageInfo' and 'configure'.
 * @param {Number} height
 *      Width of the source image at max resolution in pixels.
 * @param {Number} tileSize
 *      The size of the tiles to assumed to make up each pyramid layer in pixels.
 *      Tile size determines the point at which the image pyramid must be 
 *      divided into a matrix of smaller images.
 * @param {Number} tileOverlap
 *      The number of pixels each tile is expected to overlap touching tiles.
 * @param {Number} minLevel
 *      The minimum level to attempt to load.
 * @param {Number} maxLevel
 *      The maximum level to attempt to load.
 * @property {Number} aspectRatio
 *      Ratio of width to height
 * @property {OpenSeadragon.Point} dimensions
 *      Vector storing x and y dimensions ( width and height respectively ).
 * @property {Number} tileSize
 *      The size of the image tiles used to compose the image.
 * @property {Number} tileOverlap
 *      The overlap in pixels each tile shares with it's adjacent neighbors.
 * @property {Number} minLevel
 *      The minimum pyramid level this tile source supports or should attempt to load.
 * @property {Number} maxLevel
 *      The maximum pyramid level this tile source supports or should attempt to load.
 */ 
$.TileSource = function( width, height, tileSize, tileOverlap, minLevel, maxLevel ) {
    var _this = this,
        callback = null,
        readyHandler = null,
        args = arguments,
        options,
        i;

    if( $.isPlainObject( width ) ){
        options = width;
    }else{
        options = {
            width: args[0],
            height: args[1],
            tileSize: args[2],
            tileOverlap: args[3],
            minLevel: args[4],
            maxLevel: args[5]
        };
    }

    //Tile sources supply some events, namely 'ready' when they must be configured
    //by asyncronously fetching their configuration data.
    $.EventHandler.call( this );

    //we allow options to override anything we dont treat as
    //required via idiomatic options or which is functionally
    //set depending on the state of the readiness of this tile
    //source
    $.extend( true, this, options );

    //Any functions that are passed as arguments are bound to the ready callback
    /*jshint loopfunc:true*/
    for( i = 0; i < arguments.length; i++ ){
        if( $.isFunction( arguments[i] ) ){
            callback = arguments[ i ];
            this.addHandler( 'ready', function( placeHolderSource, readySource ){
                callback( readySource );
            });
            //only one callback per constructor
            break;
        }
    }

    if( 'string' == $.type( arguments[ 0 ] ) ){
        //in case the getImageInfo method is overriden and/or implies an
        //async mechanism set some safe defaults first
        this.aspectRatio = 1;
        this.dimensions  = new $.Point( 10, 10 );
        this.tileSize    = 0;
        this.tileOverlap = 0;
        this.minLevel    = 0;
        this.maxLevel    = 0;
        this.ready       = false;
        //configuration via url implies the extending class 
        //implements and 'configure'
        this.getImageInfo( arguments[ 0 ] );

    } else {
    
        //explicit configuration via positional args in constructor
        //or the more idiomatic 'options' object
        this.ready       = true;
        this.aspectRatio = ( options.width && options.height ) ? 
            (  options.width / options.height ) : 1;
        this.dimensions  = new $.Point( options.width, options.height );
        this.tileSize    = options.tileSize ? options.tileSize : 0;
        this.tileOverlap = options.tileOverlap ? options.tileOverlap : 0;
        this.minLevel    = options.minLevel ? options.minLevel : 0;
        this.maxLevel    = ( undefined !== options.maxLevel && null !== options.maxLevel ) ? 
            options.maxLevel : (
                ( options.width && options.height ) ? Math.ceil( 
                    Math.log( Math.max( options.width, options.height ) ) / 
                    Math.log( 2 ) 
                ) : 0
            );
        if( callback && $.isFunction( callback ) ){
            callback( this );
        }
    }


};


$.TileSource.prototype = {
    
    /**
     * @function
     * @param {Number} level
     */
    getLevelScale: function( level ) {

        // see https://github.com/openseadragon/openseadragon/issues/22
        // we use the tilesources implementation of getLevelScale to generate
        // a memoized re-implementation
        var levelScaleCache = {},
            i;
        for( i = 0; i <= this.maxLevel; i++ ){
            levelScaleCache[ i ] = 1 / Math.pow(2, this.maxLevel - i);
        }
        this.getLevelScale = function( _level ){
            return levelScaleCache[ _level ];
        };
        return this.getLevelScale( level );
    },

    /**
     * @function
     * @param {Number} level
     */
    getNumTiles: function( level ) {
        var scale = this.getLevelScale( level ),
            x = Math.ceil( scale * this.dimensions.x / this.tileSize ),
            y = Math.ceil( scale * this.dimensions.y / this.tileSize );

        return new $.Point( x, y );
    },

    /**
     * @function
     * @param {Number} level
     */
    getPixelRatio: function( level ) {
        var imageSizeScaled = this.dimensions.times( this.getLevelScale( level ) ),
            rx = 1.0 / imageSizeScaled.x,
            ry = 1.0 / imageSizeScaled.y;

        return new $.Point(rx, ry);
    },


    /**
     * @function
     * @param {Number} level
     */
    getClosestLevel: function( rect ) {
        var i,
            tilesPerSide = Math.floor( Math.max( rect.x, rect.y ) / this.tileSize ),
            tiles;
        for( i = this.minLevel; i < this.maxLevel; i++ ){
            tiles = this.getNumTiles( i );
            if( Math.max( tiles.x, tiles.y ) + 1 >= tilesPerSide ){
                break;
            }
        }
        return Math.max( 0, i - 1 );
    },

    /**
     * @function
     * @param {Number} level
     * @param {OpenSeadragon.Point} point
     */
    getTileAtPoint: function( level, point ) {
        var pixel = point.times( this.dimensions.x ).times( this.getLevelScale(level ) ),
            tx = Math.floor( pixel.x / this.tileSize ),
            ty = Math.floor( pixel.y / this.tileSize );

        return new $.Point( tx, ty );
    },

    /**
     * @function
     * @param {Number} level
     * @param {Number} x
     * @param {Number} y
     */
    getTileBounds: function( level, x, y ) {
        var dimensionsScaled = this.dimensions.times( this.getLevelScale( level ) ),
            px = ( x === 0 ) ? 0 : this.tileSize * x - this.tileOverlap,
            py = ( y === 0 ) ? 0 : this.tileSize * y - this.tileOverlap,
            sx = this.tileSize + ( x === 0 ? 1 : 2 ) * this.tileOverlap,
            sy = this.tileSize + ( y === 0 ? 1 : 2 ) * this.tileOverlap,
            scale = 1.0 / dimensionsScaled.x;

        sx = Math.min( sx, dimensionsScaled.x - px );
        sy = Math.min( sy, dimensionsScaled.y - py );

        return new $.Rect( px * scale, py * scale, sx * scale, sy * scale );
    },
    

    /**
     * Responsible for retrieving, and caching the
     * image metadata pertinent to this TileSources implementation.
     * @function
     * @param {String} url
     * @throws {Error}
     */
    getImageInfo: function( url ) {
        var _this   = this,
            error,
            callbackName,
            callback,
            readySource,
            options,
            urlParts,
            filename,
            lastDot,
            tilesUrl;


        if( url ) {
            urlParts = url.split( '/' );
            filename = urlParts[ urlParts.length - 1 ];
            lastDot  = filename.lastIndexOf( '.' );
            if ( lastDot > -1 ) {
                urlParts[ urlParts.length - 1 ] = filename.slice( 0, lastDot );
            }
        }
    
        callback = function( data ){
            var $TileSource = $.TileSource.determineType( _this, data, url );
            options = $TileSource.prototype.configure.apply( _this, [ data, url ]);
            readySource = new $TileSource( options );
            _this.ready = true;
            _this.raiseEvent( 'ready', readySource );
        };

        if( url.match(/\.js$/) ){
            //TODO: Its not very flexible to require tile sources to end jsonp
            //      request for info  with a url that ends with '.js' but for
            //      now it's the only way I see to distinguish uniformly.
            callbackName = url.split( '/' ).pop().replace('.js','');
            $.jsonp({
                url: url,
                async: false,
                callbackName: callbackName,
                callback: callback
            });
        } else {
            // request info via xhr asyncronously.
            $.makeAjaxRequest( url, function( xhr ) {
                var data = processResponse( xhr );
                callback( data );
            });
        }

    },

    /**
     * Responsible determining if a the particular TileSource supports the
     * data format ( and allowed to apply logic against the url the data was
     * loaded from, if any ). Overriding implementations are expected to do
     * something smart with data and / or url to determine support.  Also
     * understand that iteration order of TileSources is not guarunteed so
     * please make sure your data or url is expressive enough to ensure a simple
     * and sufficient mechanisim for clear determination.
     * @function
     * @param {String|Object|Array|Document} data
     * @param {String} url - the url the data was loaded 
     *      from if any.
     * @return {Boolean}
     */
    supports: function( data, url ) {
        return false;
    },

    /**
     * Responsible for parsing and configuring the
     * image metadata pertinent to this TileSources implementation.
     * This method is not implemented by this class other than to throw an Error
     * announcing you have to implement it.  Because of the variety of tile 
     * server technologies, and various specifications for building image
     * pyramids, this method is here to allow easy integration.
     * @function
     * @param {String|Object|Array|Document} data
     * @param {String} url - the url the data was loaded 
     *      from if any.
     * @return {Object} options - A dictionary of keyword arguments sufficient 
     *      to configure this tile sources constructor.
     * @throws {Error}
     */
    configure: function( data, url ) {
        throw new Error( "Method not implemented." );
    },

    /**
     * Responsible for retriving the url which will return an image for the 
     * region speified by the given x, y, and level components.
     * This method is not implemented by this class other than to throw an Error
     * announcing you have to implement it.  Because of the variety of tile 
     * server technologies, and various specifications for building image
     * pyramids, this method is here to allow easy integration.
     * @function
     * @param {Number} level
     * @param {Number} x
     * @param {Number} y
     * @throws {Error}
     */
    getTileUrl: function( level, x, y ) {
        throw new Error( "Method not implemented." );
    },

    /**
     * @function
     * @param {Number} level
     * @param {Number} x
     * @param {Number} y
     */
    tileExists: function( level, x, y ) {
        var numTiles = this.getNumTiles( level );
        return  level >= this.minLevel && 
                level <= this.maxLevel &&
                x >= 0 && 
                y >= 0 && 
                x < numTiles.x && 
                y < numTiles.y;
    }
};


$.extend( true, $.TileSource.prototype, $.EventHandler.prototype );


/**
 * Decides whether to try to process the response as xml, json, or hand back
 * the text
 * @eprivate
 * @inner
 * @function
 * @param {XMLHttpRequest} xhr - the completed network request
 */
function processResponse( xhr ){
    var responseText = xhr.responseText,
        status       = xhr.status,
        statusText,
        data;

    if ( !xhr ) {
        throw new Error( $.getString( "Errors.Security" ) );
    } else if ( xhr.status !== 200 && xhr.status !== 0 ) {
        status     = xhr.status;
        statusText = ( status == 404 ) ? 
            "Not Found" : 
            xhr.statusText;
        throw new Error( $.getString( "Errors.Status", status, statusText ) );
    }

    if( responseText.match(/\s*<.*/) ){
        try{
        data = ( xhr.responseXML && xhr.responseXML.documentElement ) ? 
            xhr.responseXML : 
            $.parseXml( responseText );
        } catch (e){
            data = xhr.responseText;
        }
    }else if( responseText.match(/\s*[\{\[].*/) ){
        /*jshint evil:true*/
        data = eval( '('+responseText+')' );
    }else{
        data = responseText;
    }
    return data;
}


/**
 * Determines the TileSource Implementation by introspection of OpenSeadragon
 * namespace, calling each TileSource implementation of 'isType'
 * @eprivate
 * @inner
 * @function
 * @param {Object|Array|Document} data - the tile source configuration object
 * @param {String} url - the url where the tile source configuration object was
 *      loaded from, if any.
 */
$.TileSource.determineType = function( tileSource, data, url ){
    var property;
    for( property in OpenSeadragon ){
        if( property.match(/.+TileSource$/) &&
            $.isFunction( OpenSeadragon[ property ] ) &&
            $.isFunction( OpenSeadragon[ property ].prototype.supports ) &&
            OpenSeadragon[ property ].prototype.supports.call( tileSource, data, url )
        ){
            return OpenSeadragon[ property ];
        }
    }
};


}( OpenSeadragon ));