/** 
 * HTML module.
 * @module html
 */
var dwv = dwv || {};
dwv.html = dwv.html || {};

/**
 * Window layer.
 * @class Layer
 * @namespace dwv.html
 * @constructor
 * @param {String} name The name of the layer.
 */
dwv.html.Layer = function(name)
{
    /**
     * The associated HTMLCanvasElement.
     * @property canvas
     * @private
     * @type Object
     */
    var canvas = null;
    /**
     * A cache of the initial canvas.
     * @property cacheCanvas
     * @private
     * @type Object
     */
    var cacheCanvas = null;
    /**
     * The associated CanvasRenderingContext2D.
     * @property context
     * @private
     * @type Object
     */
    var context = null;
    
    /**
     * Get the layer name.
     * @method getName
     * @return {String} The layer name.
     */
    this.getName = function() { return name; };
    /**
     * Get the layer canvas.
     * @method getCanvas
     * @return {Object} The layer canvas.
     */
    this.getCanvas = function() { return canvas; };
    /**
     * Get the layer context.
     * @method getContext
     * @return {Object} The layer context.
     */
    this.getContext = function() { return context; };
    /**
     * Get the layer offset on page.
     * @method getOffset
     * @return {Number} The layer offset on page.
     */
    this.getOffset = function() { return $('#'+name).offset(); };

    /**
     * The image data array.
     * @property imageData
     * @private
     * @type Array
     */
    var imageData = null;
    
    /**
     * The layer origin.
     * @property origin
     * @private
     * @type {Object}
     */
    var origin = {'x': 0, 'y': 0};
    /**
     * Get the layer origin.
     * @method getOrigin
     * @returns {Object} The layer origin as {'x','y'}.
     */
    this.getOrigin = function () {
        return origin;
    };
    /**
     * The image zoom.
     * @property zoom
     * @private
     * @type {Object}
     */
    var zoom = {'x': 1, 'y': 1};
    /**
     * Get the layer zoom.
     * @method getZoom
     * @returns {Object} The layer zoom as {'x','y'}.
     */
    this.getZoom = function () {
        return zoom;
    };
    
    /**
     * Set the canvas width.
     * @method setWidth
     * @param {Number} width The new width.
     */
    this.setWidth = function ( width ) {
        canvas.width = width;
    };
    /**
     * Set the canvas height.
     * @method setHeight
     * @param {Number} height The new height.
     */
    this.setHeight = function ( height ) {
        canvas.height = height;
    };
    
    /**
     * Set the layer zoom.
     * @method setZoom
     * @param {Number} newZoomX The zoom in the X direction.
     * @param {Number} newZoomY The zoom in the Y direction.
     * @param {Number} centerX The zoom center in the X direction.
     * @param {Number} centerY The zoom center in the Y direction.
     */
    this.zoom = function(newZoomX,newZoomY,centerX,centerY)
    {
        // The zoom is the ratio between the differences from the center
        // to the origins:
        // centerX - originX = ( centerX - originX0 ) * zoomX
        // (center in ~world coordinate system)  
        //originX = (centerX / zoomX) + originX - (centerX / newZoomX);
        //originY = (centerY / zoomY) + originY - (centerY / newZoomY);
        
        // center in image coordinate system        
        origin.x = centerX - (centerX - origin.x) * (newZoomX / zoom.x);
        origin.y = centerY - (centerY - origin.y) * (newZoomY / zoom.y);

        // save zoom
        zoom.x = newZoomX;
        zoom.y = newZoomY;
    };
    
    /**
     * Set the layer translation.
     * Translation is according to the last one.
     * @method setTranslate
     * @param {Number} tx The translation in the X direction.
     * @param {Number} ty The translation in the Y direction.
     */
    this.translate = function(tx,ty)
    {
        // new origin
        origin.x += tx * zoom.x;
        origin.y += ty * zoom.y;
    };
    
    /**
     * Set the image data array.
     * @method setImageData
     * @param {Array} data The data array.
     */
    this.setImageData = function(data)
    {
        imageData = data;
        // update the cached canvas
        cacheCanvas.getContext("2d").putImageData(imageData, 0, 0);
    };
    
    /**
     * Reset the layout.
     * @method resetLayout
     */ 
    this.resetLayout = function(izoom)
    {
        origin.x = 0;
        origin.y = 0;
        zoom.x = izoom;
        zoom.y = izoom;
    };
    
    /**
     * Transform a display position to an index.
     * @method displayToIndex
     */ 
    this.displayToIndex = function ( point2D ) {
        return {'x': (point2D.x - origin.x) / zoom.x,
            'y': (point2D.y - origin.y) / zoom.y };
    };
    
    /**
     * Draw the content (imageData) of the layer.
     * The imageData variable needs to be set
     * @method draw
     */
    this.draw = function ()
    {
        // clear the context: reset the transform first
        // store the current transformation matrix
        context.save();
        // use the identity matrix while clearing the canvas
        context.setTransform( 1, 0, 0, 1, 0, 0 );
        context.clearRect( 0, 0, canvas.width, canvas.height );
        // restore the transform
        context.restore();
        
        // draw the cached canvas on the context
        // transform takes as input a, b, c, d, e, f to create
        // the transform matrix (column-major order):
        // [ a c e ]
        // [ b d f ]
        // [ 0 0 1 ]
        context.setTransform( zoom.x, 0, 0, zoom.y, origin.x, origin.y );
        context.drawImage( cacheCanvas, 0, 0 );
    };
    
    /**
     * Initialise the layer: set the canvas and context
     * @method initialise
     * @input {Number} inputWidth The width of the canvas.
     * @input {Number} inputHeight The height of the canvas.
     */
    this.initialise = function(inputWidth, inputHeight)
    {
        // find the canvas element
        canvas = document.getElementById(name);
        if (!canvas)
        {
            alert("Error: cannot find the canvas element for '" + name + "'.");
            return;
        }
        // check that the getContext method exists
        if (!canvas.getContext)
        {
            alert("Error: no canvas.getContext method for '" + name + "'.");
            return;
        }
        // get the 2D context
        context = canvas.getContext('2d');
        if (!context)
        {
            alert("Error: failed to get the 2D context for '" + name + "'.");
            return;
        }
        // canvas sizes
        canvas.width = inputWidth;
        canvas.height = inputHeight;
        // original empty image data array
        context.clearRect (0, 0, canvas.width, canvas.height);
        imageData = context.getImageData(0, 0, canvas.width, canvas.height);
        // cached canvas
        cacheCanvas = document.createElement("canvas");
        cacheCanvas.width = inputWidth;
        cacheCanvas.height = inputHeight;
    };
    
    /**
     * Fill the full context with the current style.
     * @method fillContext
     */
    this.fillContext = function()
    {
        context.fillRect( 0, 0, canvas.width, canvas.height );
    };
    
    /**
     * Clear the context and reset the image data.
     * @method clear
     */
    this.clear = function()
    {
        context.clearRect(0, 0, canvas.width, canvas.height);
        imageData = context.getImageData(0, 0, canvas.width, canvas.height);
        this.resetLayout();
    };

    /**
     * Merge two layers.
     * @method merge
     * @input {Layer} layerToMerge The layer to merge. It will also be emptied.
     */
    this.merge = function(layerToMerge)
    {
        // basic resampling of the merge data to put it at zoom 1:1
        var mergeImageData = layerToMerge.getContext().getImageData(
            0, 0, canvas.width, canvas.height);
        var offMerge = 0;
        var offMergeJ = 0;
        var offThis = 0;
        var offThisJ = 0;
        var alpha = 0;
        for( var j=0; j < canvas.height; ++j ) {
            offMergeJ = parseInt( (origin.y + j * zoom.y), 10 ) * canvas.width;
            offThisJ = j * canvas.width;
            for( var i=0; i < canvas.width; ++i ) {
                // 4 component data: RGB + alpha
                offMerge = 4 * ( parseInt( (origin.x + i * zoom.x), 10 ) + offMergeJ );
                offThis = 4 * ( i + offThisJ );
                // merge non transparent 
                alpha = mergeImageData.data[offMerge+3];
                if( alpha !== 0 ) {
                    imageData.data[offThis] = mergeImageData.data[offMerge];
                    imageData.data[offThis+1] = mergeImageData.data[offMerge+1];
                    imageData.data[offThis+2] = mergeImageData.data[offMerge+2];
                    imageData.data[offThis+3] = alpha;
                }
            }
        }
        // empty and reset merged layer
        layerToMerge.clear();
        // draw the layer
        this.draw();
    };
    
    /**
     * Set the line color for the layer.
     * @method setLineColor
     * @input {String} color The line color.
     */
    this.setLineColor = function(color)
    {
        context.fillStyle = color;
        context.strokeStyle = color;
    };
    
    /**
     * Display the layer.
     * @method setStyleDisplay
     * @input {Boolean} val Whether to display the layer or not.
     */
    this.setStyleDisplay = function(val)
    {
        if( val === true )
        {
            canvas.style.display = '';
        }
        else
        {
            canvas.style.display = "none";
        }
    };
    
    /**
     * Check if the layer is visible.
     * @method isVisible
     * @return {Boolean} True if the layer is visible.
     */
    this.isVisible = function()
    {
        if( canvas.style.display === "none" ) {
            return false;
        }
        else {
            return true;
        }
    };
    
    /**
     * Align on another layer.
     * @method align
     * @param {Layer} rhs The layer to align on.
     */
    this.align = function(rhs)
    {
        canvas.style.top = rhs.getCanvas().offsetTop;
        canvas.style.left = rhs.getCanvas().offsetLeft;
    };
}; // Layer class

/**
 * Get the offset of an input event.
 * @method getEventOffset
 * @static
 * @param {Object} event The event to get the offset from.
 * @return {Array} The array of offsets.
 */
dwv.html.getEventOffset = function (event) {
    var positions = [];
    var ex = 0;
    var ey = 0;
    if ( event.targetTouches ) {
        var touch = null;
        for ( var i = 0 ; i < event.targetTouches.length; ++i ) {
            touch = event.targetTouches[i];
            ex = touch.pageX - app.getImageLayer().getOffset().left;
            ey = touch.pageY - app.getImageLayer().getOffset().top;
            positions.push({'x': ex, 'y': ey});
        }
    }
    else {
        // layerX is used by Firefox
        ex = event.offsetX === undefined ? event.layerX : event.offsetX;
        ey = event.offsetY === undefined ? event.layerY : event.offsetY;
        positions.push({'x': ex, 'y': ey});
    }
    return positions;
};