/**
 * This is the class responsible for Seam curving- Context Aware Image Resizing  
 */
function ImageResizer(imgUrl, canvasDiv) 
{
	//this.SEAM_URL = "http://localhost/seam/image";
	this.SEAM_URL = "seamJSON.js"
	//console.log("Initializing " + canvasDiv + " with image " + imgUrl);
	this.imgUrl = imgUrl;
	this.canvasDiv = canvasDiv; 
	this.canvasContext = this.canvasDiv.getContext("2d");
	this.drawImage(this.imgUrl);
	this.originalWidth = this.canvasDiv.width;
	this.originalHeight = this.canvasDiv.height;
	this.ready = false;
}

/**
 * Draws the actual image onto the canvas
 * @param {String} imageUrl
 */
ImageResizer.prototype.drawImage = function(imageUrl)
{
	//console.log("Drawing image");
	var img = new Image();
	img.src = imageUrl;
	var imgResizer = this;
	img.onload = function()
	{
		//console.log("Image Loaded");
		imgResizer.canvasContext.drawImage(img,0,0);
		imgResizer.imageData = imgResizer.canvasContext.getImageData(0,0,img.width,img.height);
		imgResizer.originalImageData = imgResizer.canvasContext.getImageData(0,0,img.width,img.height);
		imgResizer.getSeams(imageUrl);
	};
};

/**
 * Gets the seams of the current image by analysing the image 
 * on the server. This uses AJAX for doing this
 */
ImageResizer.prototype.getSeams = function(imageUrl)
{
	//console.log("Getting Seam data from Server");
	var xmlHttp = null;
	try
	{
		// Firefox, Opera 8.0+, Safari
		xmlHttp=new XMLHttpRequest();
	}
	catch (e)
	{
		// Internet Explorer
		try
		{
			xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
		}
		catch (e)
		{
			try{xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");}
			catch (e){}
		}
	}

	if (xmlHttp == null)
	{
		return null;
	}
	
	var imgResizer = this;
	xmlHttp.onreadystatechange = function(){imgResizer.onGetSeamHandler.call(imgResizer,xmlHttp);}
	xmlHttp.open("GET", this.SEAM_URL + "?imageUrl=" + imageUrl);
	xmlHttp.send(null);
}

ImageResizer.prototype.onGetSeamHandler = function(o)
{
	//console.log("");
	this.seamData = eval("(" + o.responseText + ")");
	this.ready = true;
}

/**
 * Resizes the image by removing or adding the appropriate seams
 * @param {int} width
 * @param {int} height
 */
ImageResizer.prototype.resizeReduce= function(widthDiff, heightDiff)
{
	if (this.ready == false)
	{
		return;
	}
	//console.log("Resizing image ...");
	
	var newImage = {};
	newImage.width = this.imageData.width;
	newImage.height = this.imageData.height;
	
	for (y =0; y < this.originalHeight; y++)
	{
		var x1 = 0; // x counter of the new image
		for (var x = 0;x < this.originalWidth; x++)
		{
			var isXskippable = false;
			for (var i = 0; i < widthDiff; i++)
			{
				if (this.seamData.topDownSeam[i][y] == x)
				{
					isXskippable = true;
					break;
				} 
			}
			if (isXskippable == false)
			{
				// this has not been skipped, so place this pixel
				this.putPixel(x1,y,this.getPixel(x,y));
				x1++;
			}
		}
	}

	this.canvasContext.putImageData(this.imageData, 0,0);
	this.canvasContext.clearRect(this.originalWidth-widthDiff, 0, this.originalWidth, this.originalHeight);
	this.originalWidth = this.originalWidth - widthDiff;
	//console.log("Resize complete from  (" + this.canvasDiv.width + ", " + this.canvasDiv.height + ") to (" + x1 + ", " + y + ")");
};

/**
 * Shows the nth seam in the current image
 * @param {Object} number
 */
ImageResizer.prototype.showSeam = function(n)
{
	//console.log("Showing seam " + n);
	for (y = 0; y < this.originalWidth; y++)
	{
		var color = {'red' : 0, 'blue' : 100, 'green': 100, 'alpha' : 1};
		this.putPixel(this.seamData.topDownSeam[n][y], y , color);
		
	}
	this.canvasContext.putImageData(this.imageData, 0,0);
	//console.log("Seam shown");
}

/**
 * Gets the pixel at the current location
 * @param {Object} x
 * @param {Object} y
 */
ImageResizer.prototype.getPixel = function(x,y)
{
	var base = (y * this.imageData.width + x) * 4;
	var rgba = {};
	
	rgba.red = this.imageData.data[base + 0]
	rgba.blue = this.imageData.data[base + 1]
	rgba.green = this.imageData.data[base + 2]
	rgba.alpha = this.imageData.data[base + 3]
	return rgba;
}

/**
 * Puts a specific value in the 
 * @param {int} x
 * @param {int} y
 * @param {rgba  {'red' : 'int', 'blue':'int'; 'green' : 'int', 'alpha': ''}} rgba
 */

ImageResizer.prototype.putPixel = function(x,y, rgba, imageData)
{
	if (typeof(imageData) == "undefined")
	{
		imageData = this.imageData;
	}
	
	var base = (y * imageData.width + x) * 4;
	imageData.data[base + 0] = rgba.red;
	imageData.data[base + 1] = rgba.blue;
	imageData.data[base + 2] = rgba.green;
	imageData.data[base + 3] = rgba.alpha;
};