(function ($) {
	$.fn.darkbox = function () {
		var shadowFadeInTime  = 200,
			shadowFadeOutTime = 100,
			imageFadeInTime = 400,
			imageErrorFadeOutTime = 800,
			darkboxStateClasses = 'darkbox-on darkbox-done darkbox-loaded darkbox-error',
			boxMargin = 50, // For cases, when image is bigger than viewport

			buttonPlaceClass = /mac/i.test( navigator.platform ) ?
				'darkbox-button-left' :
				'darkbox-button-right',

			darkbox,
			darkboxShadow,
			darkboxCanvas,
			darkboxImage,
			darkboxButton,
			spinnerAnimationIntervalId = 0,
			spinnerStep = 0;

		function prepareDarkbox() {
			$('.darkbox').remove();

			$('<div class="darkbox"><div class="darkbox-shadow"></div><div class="darkbox-canvas"><img alt="">'
				+ '<div class="darkbox-button" title="Close"></div></div></div>')
				.appendTo('body');

			darkbox = $('div.darkbox');
			darkboxShadow = darkbox.children('div.darkbox-shadow');
			darkboxCanvas = darkbox.children('div.darkbox-canvas');
			darkboxImage = darkboxCanvas.children('img');
			darkboxButton = darkboxCanvas.children('div.darkbox-button');
			spinnerAnimationIntervalId = 0;
			spinnerStep = 0;

			// Darkbox handlers
			darkboxShadow
				.css('opacity', 0)
				.click(closeBox);

			darkboxButton
				.addClass(buttonPlaceClass)
				.click(closeBox);
		}

		function resetCanvasBackgroundChanges() {
			if (darkboxCanvas) {
				clearInterval(spinnerAnimationIntervalId);
				darkboxCanvas.css('background-position', '24px 24px');
			}
		}

		function openBox(e) {
			e.preventDefault();

			prepareDarkbox();
			var link = $(this);
			darkbox.addClass('darkbox-on');

			darkboxCanvas.css({
				'width': '',
				'marginLeft': '',
				'height': '',
				'marginTop': '',
				'opacity': 0.5
			});

			// FIXME: Constants for initial shift, step height, number of
			// steps, interval?
			spinnerAnimationIntervalId = setInterval(function() {
				var shift = 24 - (56 * spinnerStep);
				darkboxCanvas.css('background-position', '24px ' + shift + 'px');
				spinnerStep = (7 <= spinnerStep) ? 0 : spinnerStep + 1;
			}, 90);

			darkboxImage
				.load(handleImageLoad)
				.one('error', handleImageLoadError)
				.css({ 'width': '', 'height': '' })
				.attr('alt', link.attr('title') || '')
				.attr('src', link.attr('href'));

			darkboxShadow.animate({ 'opacity': 0.6 }, shadowFadeInTime);
		}

		function closeBox() {
			resetCanvasBackgroundChanges();

			if (darkboxShadow) {
				darkboxShadow.animate(
					{ opacity: 0 },
					shadowFadeOutTime,
					function() {
						darkbox.removeClass(darkboxStateClasses);
						darkboxCanvas.stop(); // Stop animation on close
					}
				);
			}
		}

		function handleKey(e) {
			// Close darkbox on space (32) and esc (27)
			if (27 === e.which || 32 === e.which) {
				// If darkbox is visible
				if ($('div.darkbox:visible').size()) {
					e.preventDefault();
					closeBox();
				}
			}
		}

		function handleImageLoadError() {
			resetCanvasBackgroundChanges();

			darkbox.addClass('darkbox-error');
			setTimeout(closeBox, imageErrorFadeOutTime);
		}

		function handleImageLoad() {
			resetCanvasBackgroundChanges();

			var img = $(this),
				ratio = 1,
				imgWidth = img.width(),
				imgHeight = img.height(),
				darkboxWidth = darkbox.width(),
				darkboxHeight = darkbox.height();

			// Sometimes IE fires load event before loading image.
			if (0 === imgWidth && 0 === imgHeight) {
				setTimeout(function(){ img.load(); }, 10);
				return;
			}

			// We must downsize the image when it is bigger than viewport
			if (
				(imgWidth > darkboxWidth - boxMargin) ||
				(imgHeight > darkboxHeight - boxMargin)
			) {
				ratio = Math.min(
					(darkboxWidth - boxMargin) / imgWidth,
					(darkboxHeight - boxMargin) / imgHeight
				);

				imgWidth = Math.round(imgWidth * ratio);
				imgHeight = Math.round(imgHeight * ratio);
			}

			darkbox.addClass('darkbox-loaded');

			// NOTE: we must show darkboxCanvas to compute dimensions right
			darkboxCanvas
				.animate(
					{
						width: imgWidth,
						marginLeft: -imgWidth / 2,
						height: imgHeight,
						marginTop:  -imgHeight / 2,
						opacity: 1
					},
					imageFadeInTime,
					function() {
						darkbox.addClass('darkbox-done');
					}
				);
		}

		// FIXME: need better solution
		// Opera preventDefault for space on keypress
		// Safari reacts on esc only on keydown
		$(document)
			.keypress(handleKey)
			.keydown(handleKey);

		this.click(openBox);
		return this; // Support chaining
	};
}(jQuery));