/*
    Ken Burns effect JQuery plugin
    Copyright (C) 2011 Will McGugan http://www.willmcgugan.com

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License as
    published by the Free Software Foundation, either version 3 of the
    License, or (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Affero General Public License for more details.

    You should have received a copy of the GNU Affero General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

(function($){
	
	$.fn.kenburns = function(options) {
		
		var $canvas = $(this);
		var ctx = this[0].getContext('2d');
		var start_time = null;
		var width = $canvas.width();
		var height = $canvas.height();		
						
		var image_paths = options.images;		
		var display_time = options.display_time || 7000;
		var fade_time = Math.min(display_time / 2, options.fade_time || 1000);
		var solid_time = display_time - (fade_time * 2);
		var fade_ratio = fade_time - display_time
		var frames_per_second = options.frames_per_second || 30;		
		var frame_time = (1 / frames_per_second) * 1000;
		var zoom_level = 1 / (options.zoom || 2);
		var clear_color = options.background_color || '#000000';	
		
		var images = [];
		$(image_paths).each(function(i, image_path){
			images.push({path:image_path,
						 initialized:false,
						 loaded:false});
		});		
		function get_time() {
			var d = new Date();
			return d.getTime() - start_time;
		}
		
		function interpolate_point(x1, y1, x2, y2, i) {
			// Finds a point between two other points
			return  {x: x1 + (x2 - x1) * i,
					 y: y1 + (y2 - y1) * i}
		}
		
		function interpolate_rect(r1, r2, i) {
			// Blend one rect in to another
			var p1 = interpolate_point(r1[0], r1[1], r2[0], r2[1], i);
			var p2 = interpolate_point(r1[2], r1[3], r2[2], r2[3], i);
			return [p1.x, p1.y, p2.x, p2.y];
		}
		
		function scale_rect(r, scale) {
			// Scale a rect around its center
			var w = r[2] - r[0];
			var h = r[3] - r[1];
			var cx = (r[2] + r[0]) / 2;
			var cy = (r[3] + r[1]) / 2;
			var scalew = w * scale;
			var scaleh = h * scale;
			return [cx - scalew/2,
					cy - scaleh/2,
					cx + scalew/2,
					cy + scaleh/2];		
		}
		
		function fit(src_w, src_h, dst_w, dst_h) {
			// Finds the best-fit rect so that the destination can be covered
			var src_a = src_w / src_h;
			var dst_a = dst_w / dst_h;			
			var w = src_h * dst_a;
			var h = src_h;						
			if (w > src_w)
			{
				var w = src_w;
				var h = src_w / dst_a;
			}						
			var x = (src_w - w) / 2;
			var y = (src_h - h) / 2;
			return [x, y, x+w, y+h]; 
		}				
		
		function get_image_info(image_index, load_callback) {
			// Gets information structure for a given index
			// Also loads the image asynchronously, if required		
			var image_info = images[image_index];
			if (!image_info.initialized) {
				var image = new Image();
				image_info.image = image;
				image_info.loaded = false;
				image.onload = function(){
					image_info.loaded = true;
					var iw = image.width;
					var ih = image.height;
										 				
					var r1 = fit(iw, ih, width, height);;
					var r2 = scale_rect(r1, zoom_level);
										
					var align_x = Math.floor(Math.random() * 3) - 1;
					var align_y = Math.floor(Math.random() * 3) - 1;
					align_x /= 2;
					align_y /= 2;
					
					var x = r2[0];
					r2[0] += x * align_x;
					r2[2] += x * align_x; 
					
					var y = r2[1];
					r2[1] += y * align_y;
					r2[3] += y * align_y;
					
					if (image_index % 2) {
						image_info.r1 = r1;
						image_info.r2 = r2;
					}
					else {
						image_info.r1 = r2;
						image_info.r2 = r1;
					}					
					
					if(load_callback) {
						load_callback();
					}
					
				}				
				image_info.initialized = true;
				image.src = image_info.path;
			}
			return image_info;
		}
		
		function render_image(image_index, anim, fade) {
			// Renders a frame of the effect	
			if (anim > 1) {
				return;
			} 									
			var image_info = get_image_info(image_index);
			if (image_info.loaded) {						
				var r = interpolate_rect(image_info.r1, image_info.r2, anim);
				var transparency = Math.min(1, fade);
				
				if (transparency > 0) {
					ctx.save();
					ctx.globalAlpha = Math.min(1, transparency);
					ctx.drawImage(image_info.image, r[0], r[1], r[2] - r[0], r[3] - r[1], 0, 0, width, height);
					ctx.restore();
				}
			}
		}				
		
		function clear() {
			// Clear the canvas
			ctx.save();
			ctx.globalAlpha = 1;
			ctx.fillStyle = clear_color;
			ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
			ctx.restore();
		}
		
		function update() {
			// Render the next frame										
			var update_time = get_time();			
			
			var top_frame = Math.floor(update_time / (display_time - fade_time));						
			var frame_start_time = top_frame * (display_time - fade_time);			
			var time_passed = update_time - frame_start_time;
			
			function wrap_index(i) {
				return (i + images.length) % images.length;
			}
			
			if (time_passed < fade_time)
			{
				var bottom_frame = top_frame - 1;
				var bottom_frame_start_time = frame_start_time - display_time + fade_time;
				var bottom_time_passed = update_time - bottom_frame_start_time;
				if (update_time < fade_time) {
					clear();
				} else {
					render_image(wrap_index(bottom_frame), bottom_time_passed / display_time, 1);	
				}								
			}
						
			render_image(wrap_index(top_frame), time_passed / display_time, time_passed / fade_time);			
			
			if (options.post_render_callback) {
				options.post_render_callback($canvas, ctx);
			}
			
			// Pre-load the next image in the sequence, so it has loaded
			// by the time we get to it
			var preload_image = wrap_index(top_frame + 1);
			get_image_info(preload_image);					
		}
			
		// Pre-load the first two images then start a timer	
		get_image_info(0, function(){			
			get_image_info(1, function(){
				start_time = get_time();				
				setInterval(update, frame_time);	
			})					
		});						
		
	};	
	
})( jQuery );