// store object constructor
// a heatmap contains a store
// the store has to know about the heatmap
// in order to trigger heatmap updates when
// datapoints get added
function store(hmap){
    var _ = {
        // data is a two dimensional array
        // a datapoint gets saved as data[point-x-value][point-y-value]
        // the value at [point-x-value][point-y-value]
        // is the occurrence of the datapoint
        data: [],
        // tight coupling of the heatmap object
        heatmap: hmap
    };
    // the max occurrence - the heatmaps radial gradient
    // alpha transition is based on it
    this.max = 1;
    this.get = function(key){
        return _[key];
    },
    this.set = function(key, value){
        _[key] = value;
    };
};

addDataPoint: function(x, y){
    if(x < 0 || y < 0)
        return;
    var me = this,
        heatmap = me.get("heatmap"),
        data = me.get("data");
    if(!data[x])
        data[x] = [];
    if(!data[x][y])
        data[x][y] = 0;
    // if count parameter is set increment by count otherwise by 1
    data[x][y]+=(arguments.length     me.set("data", data);
    // do we have a new maximum?
    if(me.max < data[x][y]){
        me.max = data[x][y];
        // max changed, we need to redraw all existing(lower) datapoints
        heatmap.get("actx").clearRect(0,0,heatmap.get("width"),heatmap.get("height"));
        for(var one in data)
            for(var two in data[one])
                heatmap.drawAlpha(one, two, data[one][two]);
        // @TODO
        // implement feature
        // heatmap.drawLegend(); ?
        return;
    }
    heatmap.drawAlpha(x, y, data[x][y]);
},

drawAlpha: function(x, y, count){
    // storing the variables because they will be often used
    var me = this,
        r1 = me.get("radiusIn"),
        r2 = me.get("radiusOut"),
        ctx = me.get("actx"),
        max = me.get("max"),
        // create a radial gradient with the defined parameters.
        // we want to draw an alphamap
        rgr = ctx.createRadialGradient(x,y,r1,x,y,r2),
        xb = x-r2, yb = y-r2, mul = 2*r2;
    // the center of the radial gradient has .1 alpha value
    rgr.addColorStop(0, 'rgba(0,0,0,'+((count)?(count/me.store.max):'0.1')+')');
    // and it fades out to 0
    rgr.addColorStop(1, 'rgba(0,0,0,0)');
    // drawing the gradient
    ctx.fillStyle = rgr;
    ctx.fillRect(xb,yb,mul,mul);
    // finally colorize the area
    me.colorize(xb,yb);
},

rgr.addColorStop(0, 'rgba(0,0,0,'+((count)?(count/me.store.max):'0.1')+')');
// and it fades out to 0
rgr.addColorStop(1, 'rgba(0,0,0,0)');

initColorPalette: function(){
    var me = this,
        canvas = document.createElement("canvas");
    canvas.width = "1";
    canvas.height = "256";
    var ctx = canvas.getContext("2d"),
        grad = ctx.createLinearGradient(0,0,1,256),
    gradient = me.get("gradient");
    for(var x in gradient){
        grad.addColorStop(x, gradient[x]);
    }
    ctx.fillStyle = grad;
    ctx.fillRect(0,0,1,256);
    //这里太强大了，缓存了我的画板数据，然后删除了画板
    me.set("gradient", ctx.getImageData(0,0,1,256).data);
    delete canvas;
    delete grad;
    delete ctx;
},

for(var i=3; i < length; i+=4){         // [0] -> r, [1] -> g, [2] -> b, [3] -> alpha
    var alpha = imageData[i],
    offset = alpha*4;
    if(!offset)
        continue;
    // we ve started with i=3
    // set the new r, g and b values
    // 根据透明度选择配色板上的配色
    imageData[i-3]=palette[offset];
    imageData[i-2]=palette[offset+1];
    imageData[i-1]=palette[offset+2];
    // we want the heatmap to have a gradient from transparent to the colors
    // as long as alpha is lower than the defined opacity (maximum),
    // we'll use the alpha value
    imageData[i] = (alpha < opacity)?alpha:opacity;
}