var book

window.onload = function() {

	var pages = [
		"http://dev.justforcomics.com/get/image/?f=comics/extracted/oni_whiteout_melt_1/00.jpg",
		"http://dev.justforcomics.com/get/image/?f=comics/extracted/oni_whiteout_melt_1/01.jpg",
		"http://dev.justforcomics.com/get/image/?f=comics/extracted/oni_whiteout_melt_1/02.jpg",
		"http://dev.justforcomics.com/get/image/?f=comics/extracted/oni_whiteout_melt_1/03.jpg",
		"http://dev.justforcomics.com/get/image/?f=comics/extracted/oni_whiteout_melt_1/04.jpg",
		"http://dev.justforcomics.com/get/image/?f=comics/extracted/oni_whiteout_melt_1/05.jpg",
		"http://dev.justforcomics.com/get/image/?f=comics/extracted/oni_whiteout_melt_1/06.jpg"
	];

	var options = {
		displayMode: "double",
		zoomMode: "fitWidth"
	}

	book = new ComicBook("comic", pages, options);
	book.draw();
}

window.onresize = function() {
	book.draw();
}

function ComicBook(id, srcs, opts) {

	this.id = id;
	this.srcs = srcs;	

	var defaults = {
		displayMode: "double",	// single / double
		zoomMode: "fitWidth"	// manual / fitWidth
	}
	var options = merge(defaults, opts);

	var pages = [];
	var canvas;
	var context;
	
	var buffer = 4;
	var pointer = 0;
	var loaded = 0;
	
	var scale = 1;

	/* 
	 * @param {String} id The canvas ID to draw the comic on.
	 * @param {Object} srcs An array of all the comic page srcs, in order
	 * @see #preload
	 */
	ComicBook.prototype.draw = function() {
	
		// setup canvas
		canvas = document.getElementById(this.id);
		context = canvas.getContext("2d");

		// preload images if needed
		if (pages.length != this.srcs.length) this.preload(this.srcs);
		else this.drawPage();

		// add page controls
		canvas.addEventListener("click", ComicBook.prototype.navigation, false);
	}

	/*
	 * Zoom the canvas
	 * 
	 * @param new_scale {Number} Scale the canvas to this ratio
	 */
	ComicBook.prototype.zoom = function(new_scale) {
		options.zoomMode = "manual";
		scale = new_scale;
		this.drawPage();
	}
	
	/**
	 * Preload all images, draw the page only after a given number have been loaded.
	 *
	 * @param srcs {Object} srcs
	 * @see #drawPage
	 */
	ComicBook.prototype.preload = function(srcs) {

		if (srcs.length < buffer) buffer = srcs.length; // don't get stuck if the buffer level is higher than the number of pages

		srcs.forEach(function(src, i) {

			var page = new Image();
			
			page.src = src;
			
			page.onload = function() {
				pages[i] = this;loaded++;
				if (loaded == buffer) ComicBook.prototype.drawPage();
			}
		});
	}

	/**
	 * Draw the current page in the canvas
	 *
	 * TODO: break this down into drawSinglePage() & drawDoublePage()
	 * TODO: if the current browser doesn't have canvas support, use img tags
	 */
	ComicBook.prototype.drawPage = function() {
	
		var zoom_scale;
		var page = pages[pointer];
		var page2 = pages[pointer + 1];

		if (typeof page != "object") throw "invalid page";

		var width = page.width;
		
		if (options.displayMode == "double") {

			// for double page spreads, factor in the width of both pages
			if (typeof page2 == "object") width += page2.width;
			
			// if this is the last page and there is no page2, still keep the canvas wide
			else width += width;
		}

		// update the page scale if a non manual mode has been chosen
		switch(options.zoomMode) {

			case "manual":
				zoom_scale = (options.displayMode == "double") ? scale * 2 : scale;
				break;
				
			case "fitWidth":
				zoom_scale =  (window.innerWidth > width)
					  ? ((window.innerWidth - width) / window.innerWidth) + 1 // scale up if the window is wider than the page
					  : window.innerWidth / width; // scale down if the window is narrower than the page
				break;
				
			default:throw "invalid zoomMode";
		}
		
		var canvas_width  = page.width * zoom_scale;
		var canvas_height = page.height * zoom_scale;

		var page_width = (options.zoomMode == "manual") ? page.width * scale : canvas_width;
		var page_height = (options.zoomMode == "manual") ? page.height * scale : canvas_height;
		
		// make sure the canvas is always at least full screen, even if the page is more narrow than the screen
		canvas.width = (canvas_width < window.innerWidth) ? window.innerWidth : canvas_width;
		canvas.height = (canvas_height < window.innerHeight) ? window.innerHeight : canvas_height;
		
		// draw the page(s)
		context.drawImage(page, 0, 0, page_width, page_height);
		if (options.displayMode == "double" && typeof page2 == "object") context.drawImage(page2, page_width, 0, page_width, page_height);
		
	}

	/**
	 * Increment the counter and draw the page in the canvas
	 * 
	 * @see #drawPage
	 */
	ComicBook.prototype.drawNextPage = function() {
		if (pointer + 1 < pages.length) {
			pointer++;
			this.drawPage();
		}
	}

	/**
	 * Decrement the counter and draw the page in the canvas
	 *
	 * @see #drawPage
	 */
	ComicBook.prototype.drawPrevPage = function() {
		if (pointer > 0) {
			pointer--;
			this.drawPage();
		}
	}
	
	ComicBook.prototype.navigation = function(e) {

		switch (e.type) {

			case "click":
				switch (getCursorPosition(e)) {
					case "left": ComicBook.prototype.drawPrevPage(); break;
					case "right": ComicBook.prototype.drawNextPage(); break;
				}
				break;
			
			defualt: console.log(e.type);
		}
	}

	/**
	 * Figure out the cursor position relative to the canvas.
	 * 
	 * Thanks to: Mark Pilgrim & http://diveintohtml5.org/canvas.html
	 */
	function getCursorPosition(e) {
	
		var x;

		// check if page relative positions exist
		if (e.pageX) x = e.pageX;
		
		// if not figure them out
		else  x = e.clientX + document.body.scrollLeft + document.documentElement.scrollLeft;
		
		// make the position relative to the canvas
		x -= canvas.offsetLeft;
		
		// check if the user clicked on the left or right side
		return (x <= canvas.width / 2) ? 'left' : 'right';
	}

	/**
	 * Merge two arrays. Any properties in b will replace the same properties in
	 * a. New properties from b will be added to a.
	 *
	 * @param a {Object}
	 * @param b {Object}
	 */
	function merge(a, b) {
	
		if (typeof b == "undefined") b = {};

		for (prop in a) {
			if (prop in b) continue;
			b[prop] = a[prop];
		}
		
		return b;
	}
}