/**
 * StickyScroll
 * written by Rick Harris - @iamrickharris
 * 
 * Requires jQuery 1.4+
 * Disclaimer: Requires position: fixed support, so no IE6
 * 
 * Make elements stick to the top of your page as you scroll
 *
 * Usage: $(element).stickyScroll(options)
 * 
 * If the element is to be contained inside one of its parents, 
 * (you want to keep it inside the main content area, and out of the header and footer)
 * then provide a selector for that parent element
 * Ex:
 * $(element).stickyScroll({ container: '#my-wrapper' })
 * 
 * If you don't have a particular element you want the sticky element contained to,
 * but still need control of its bottom boundary, use the manual mode
 * Ex:
 * $(element).stickyScroll({ mode: 'manual', 'bottomBoundary': 100 })
 * and bottomBoundary is relative to the bottom of the document
 * 
*/

(function($) {
	$.fn.stickyScroll = function(options) {
		
		var settings = $.extend({
				mode: 'auto', // 'auto' or 'manual', but anything other than auto will be treated as manual
				container: $('body'),
				bottomBoundary: null
			}, options);
			
		// make sure user input is a jQuery object
		settings.container = $(settings.container);
		if(!settings.container.length) {
			if(console) {
				console.log('StickyScroll: the element ' + options.container + ' does not exist, we\'re throwing in the towel');
			}
			return;
		}
		
		// calculate automatic bottomBoundary
		if(settings.mode === 'auto') {
			settings.bottomBoundary = $(document).height() - settings.container.offset().top - settings.container.attr('offsetHeight');
		}
		
		return this.each(function() {
			
			var $this = $(this),
				height = $this.attr('offsetHeight'),
				topOffset = $this.offset().top,
				leftOffset = $this.offset().left;
			
			function onScroll() {
				var top = $(document).scrollTop(),
					bottom = $(document).height() - top - height;
					
				if(bottom <= settings.bottomBoundary) {
					$this.offset({ top: $(document).height() - settings.bottomBoundary - height, left: leftOffset });
					settings.container.addClass('sticky-processed');
				}
				else if(top > topOffset) {
					$this.css({
						position: 'fixed',
						left: leftOffset,
						top: 0,
						bottom: ''
					});
					settings.container.addClass('sticky-processed');
				}
				else if(top < topOffset) {
					$this.css({
						position: '',
						left: '',
						top: '',
						bottom: ''
					});
					settings.container.removeClass('sticky-processed');
				}
			};
			
			onScroll();
			$(window).scroll(onScroll);

		});
	};
})(jQuery);