//
// https://github.com/sukhoi1, 25 Jan 2016
// bicubic-img-interpolation v0.1.1 jQuery plugin

$.fn.bicubicImgInterpolation = function(settings) {
	var self = this;
	$(self).each(function() {
		if(this.tagName === "IMG") {
			var src = $(this).attr('src');
			var imgW = this.width;
			var imgH = this.height;
			$(this).after("<canvas style='display: none' width='" + imgW +  "' height='" + imgH + "'></canvas>");
			var can = $(this).next()[0];
			var callback = drawHighResolutionImgThumbnail;
			drawCanvas(can, imgW*6, imgH*6, src, callback, this, settings.crossOrigin);
		}
	});
    
	function drawCanvas(can, imgW, imgH, src, callback, imgEl, crossOrigin) {
	
		var ctx = can.getContext('2d');
		var img = new Image();
		if(crossOrigin) {
		    img.setAttribute('crossOrigin', 'anonymous'); //tainted canvases may not be exported chrome, ie will also throw security error
		}
		
		var w = imgW;
		var h = imgH;

		img.onload = function() {
			
			// Step it down several times
			var can2 = document.createElement('canvas');
			can2.width = w;
			can2.height = h;
			var ctx2 = can2.getContext('2d');
			
			// Draw it at 1/2 size 3 times (step down three times)
			ctx2.drawImage(img, 0, 0, w/2, h/2);
			ctx2.drawImage(can2, 0, 0, w/2, h/2, 0, 0, w/4, h/4);
			ctx2.drawImage(can2, 0, 0, w/4, h/4, 0, 0, w/6, h/6);
			ctx.drawImage(can2, 0, 0, w/6, h/6, 0, 0, w/6, h/6);
			if(callback) {
				callback(can, this.src, imgEl);
			}
		};
	
		img.src = src;
	};
	
	function drawHighResolutionImgThumbnail(can, attrSrc, imgEl) {
		$(imgEl).attr('src', can.toDataURL("image/png"));
		$(imgEl).attr('data-src', attrSrc);
	};
};