/**
 * jquery.scrollfollow.js
 * copyright (c) 2008 net perspective (http://kitchen.net-perspective.com/)
 * licensed under the mit license (http://www.opensource.org/licenses/mit-license.php)
 * 
 * @author r.a. ray
 *
 * @projectdescription	jquery plugin for allowing an element to animate down as the user scrolls the page.
 * 
 * @version 0.4.0
 * 
 * @requires jquery.js (tested with 1.2.6)
 * @requires ui.core.js (tested with 1.5.2)
 * 
 * @optional jquery.cookie.js (http://www.stilbuero.de/2006/09/17/cookie-plugin-for-jquery/)
 * @optional jquery.easing.js (http://gsgd.co.uk/sandbox/jquery/easing/ - tested with 1.3)
 * 
 * @param speed		int - duration of animation (in milliseconds)
 * 								default: 500
 * @param offset			int - number of pixels box should remain from top of viewport
 * 								default: 0
 * @param easing		string - any one of the easing options from the easing plugin - requires jquery easing plugin < http://gsgd.co.uk/sandbox/jquery/easing/ >
 * 								default: 'linear'
 * @param container	string - id of the containing div
 * 								default: box's immediate parent
 * @param killswitch	string - id of the on/off toggle element
 * 								default: 'killswitch'
 * @param ontext		string - killswitch text to be displayed if sliding is enabled
 * 								default: 'turn slide off'
 * @param offtext		string - killswitch text to be displayed if sliding is disabled
 * 								default: 'turn slide on'
 * @param relativeto	string - scroll animation can be relative to either the 'top' or 'bottom' of the viewport
 * 								default: 'top'
 * @param delay			int - time between the end of the scroll and the beginning of the animation in milliseconds
 * 								default: 0
 */

( function( $ ) {
	
	$.scrollfollow = function ( box, options )
	{ 
		// convert box into a jquery object
		box = $( box );
		
		// 'box' is the object to be animated
		var position = box.css( 'position' );
		
		function ani()
		{		
			// the script runs on every scroll which really means many times during a scroll.
			// we don't want multiple slides to queue up.
			box.queue( [ ] );
		
			// a bunch of values we need to determine where to animate to
			var viewportheight = parseint( $( window ).height() );	
			var pagescroll =  parseint( $( document ).scrolltop() );
			var parenttop =  parseint( box.cont.offset().top );
			var parentheight = parseint( box.cont.attr( 'offsetheight' ) );
			var boxheight = parseint( box.attr( 'offsetheight' ) + ( parseint( box.css( 'margintop' ) ) || 0 ) + ( parseint( box.css( 'marginbottom' ) ) || 0 ) );
			var anitop;
			
			// make sure the user wants the animation to happen
			if ( isactive )
			{
				// if the box should animate relative to the top of the window
				if ( options.relativeto == 'top' )
				{
					// don't animate until the top of the window is close enough to the top of the box
					if ( box.initialoffsettop >= ( pagescroll + options.offset ) )
					{
						anitop = box.initialtop;
					}
					else
					{
						anitop = math.min( ( math.max( ( -parenttop ), ( pagescroll - box.initialoffsettop + box.initialtop ) ) + options.offset ), ( parentheight - boxheight - box.paddingadjustment ) );
					}
				}
				// if the box should animate relative to the bottom of the window
				else if ( options.relativeto == 'bottom' )
				{
					// don't animate until the bottom of the window is close enough to the bottom of the box
					if ( ( box.initialoffsettop + boxheight ) >= ( pagescroll + options.offset + viewportheight ) )
					{
						anitop = box.initialtop;
					}
					else
					{
						anitop = math.min( ( pagescroll + viewportheight - boxheight - options.offset ), ( parentheight - boxheight ) );
					}
				}
				
				// checks to see if the relevant scroll was the last one
				// "-20" is to account for inaccuracy in the timeout
				if ( ( new date().gettime() - box.lastscroll ) >= ( options.delay - 20 ) )
				{
					box.animate(
						{
							top: anitop
						}, options.speed, options.easing
					);
				}
			}
		};
		
		// for user-initiated stopping of the slide
		var isactive = true;
		
		if ( $.cookie != undefined )
		{
			if( $.cookie( 'scrollfollowsetting' + box.attr( 'id' ) ) == 'false' )
			{
				var isactive = false;
				
				$( '#' + options.killswitch ).text( options.offtext )
					.toggle( 
						function ()
						{
							isactive = true;
							
							$( this ).text( options.ontext );
							
							$.cookie( 'scrollfollowsetting' + box.attr( 'id' ), true, { expires: 365, path: '/'} );
							
							ani();
						},
						function ()
						{
							isactive = false;
							
							$( this ).text( options.offtext );
							
							box.animate(
								{
									top: box.initialtop
								}, options.speed, options.easing
							);	
							
							$.cookie( 'scrollfollowsetting' + box.attr( 'id' ), false, { expires: 365, path: '/'} );
						}
					);
			}
			else
			{
				$( '#' + options.killswitch ).text( options.ontext )
					.toggle( 
						function ()
						{
							isactive = false;
							
							$( this ).text( options.offtext );
							
							box.animate(
								{
									top: box.initialtop
								}, 0
							);	
							
							$.cookie( 'scrollfollowsetting' + box.attr( 'id' ), false, { expires: 365, path: '/'} );
						},
						function ()
						{
							isactive = true;
							
							$( this ).text( options.ontext );
							
							$.cookie( 'scrollfollowsetting' + box.attr( 'id' ), true, { expires: 365, path: '/'} );
							
							ani();
						}
					);
			}
		}
		
		// if no parent id was specified, and the immediate parent does not have an id
		// options.container will be undefined. so we need to figure out the parent element.
		if ( options.container == '')
		{
			box.cont = box.parent();
		}
		else
		{
			box.cont = $( '#' + options.container );
		}
		
		// finds the default positioning of the box.
		box.initialoffsettop =  parseint( box.offset().top );
		box.initialtop = parseint( box.css( 'top' ) ) || 0;
		
		// hack to fix different treatment of boxes positioned 'absolute' and 'relative'
		if ( box.css( 'position' ) == 'relative' )
		{
			box.paddingadjustment = parseint( box.cont.css( 'paddingtop' ) ) + parseint( box.cont.css( 'paddingbottom' ) );
		}
		else
		{
			box.paddingadjustment = 0;
		}
		
		// animate the box when the page is scrolled
		$( window ).scroll( function ()
			{
				// sets up the delay of the animation
				$.fn.scrollfollow.interval = settimeout( function(){ ani();} , options.delay );
				
				// to check against right before setting the animation
				box.lastscroll = new date().gettime();
			}
		);
		
		// animate the box when the page is resized
		$( window ).resize( function ()
			{
				// sets up the delay of the animation
				$.fn.scrollfollow.interval = settimeout( function(){ ani();} , options.delay );
				
				// to check against right before setting the animation
				box.lastscroll = new date().gettime();
			}
		);

		// run an initial animation on page load
		box.lastscroll = 0;
		
		ani();
	};
	
	$.fn.scrollfollow = function ( options )
	{
		options = options || {};
		options.relativeto = options.relativeto || 'top';
		options.speed = options.speed || 500;
		options.offset = options.offset || 0;
		options.easing = options.easing || 'swing';
		options.container = options.container || this.parent().attr( 'id' );
		options.killswitch = options.killswitch || 'killswitch';
		options.ontext = options.ontext || 'turn slide off';
		options.offtext = options.offtext || 'turn slide on';
		options.delay = options.delay || 0;
		
		this.each( function() 
			{
				new $.scrollfollow( this, options );
			}
		);
		
		return this;
	};
})( jquery );