/*
 * L.TileLayer.GrayWMS is a regular tilelayer with grayscale makeover.
 */

L.TileLayer.GrayWMS = L.TileLayer.WMS.extend({
    options: {
        enableCanvas: true
    },

    initialize: function (url, options) {
        var canvasEl = document.createElement('canvas');
        if( !(canvasEl.getContext && canvasEl.getContext('2d')) ) {
            options.enableCanvas = false;
        }

        L.TileLayer.WMS.prototype.initialize.call(this, url, options);
    },

    _loadTile: function (tile, tilePoint) {
        tile.setAttribute('crossorigin', 'anonymous');
        L.TileLayer.prototype._loadTile.call(this, tile, tilePoint);
    },

    _tileOnLoad: function () {
        if (this._layer.options.enableCanvas && !this.canvasContext) {
            var canvas = document.createElement("canvas");
            canvas.width = canvas.height = this._layer.options.tileSize;
            this.canvasContext = canvas.getContext("2d");
        }
        var ctx = this.canvasContext;

        if (ctx) {
            this.onload  = null; // to prevent an infinite loop
            ctx.drawImage(this, 0, 0);
            var imgd = ctx.getImageData(0, 0, this._layer.options.tileSize, this._layer.options.tileSize);
            var pix = imgd.data;
            for (var i = 0, n = pix.length; i < n; i += 4) {
                pix[i] = pix[i + 1] = pix[i + 2] = (3 * pix[i] + 4 * pix[i + 1] + pix[i + 2]) / 8;
                //pix[i] = pix[i + 1] = pix[i + 2] = (2 * pix[i] + 3 * pix[i + 1] + 3 * pix[i + 2]) / 6;
            }
            ctx.putImageData(imgd, 0, 0);
            this.removeAttribute("crossorigin");
            this.src = ctx.canvas.toDataURL();
        }

        L.TileLayer.prototype._tileOnLoad.call(this);
    }
});

L.tileLayer.graywms = function (url, options) {
    return new L.TileLayer.GrayWMS(url, options);
};