/**
 * 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.css(
                        {
                            top: aniTop
                        }
                    );
                }
            }
        };
        
        // 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.css(
                                {
                                    top: box.initialTop
                                }
                            );    
                            
                            $.cookie( 'scrollFollowSetting' + box.attr( 'id' ), false, { expires: 365, path: '/'} );
                        }
                    );
            }
            else
            {
                $( '#' + options.killSwitch ).text( options.onText )
                    .toggle( 
                        function ()
                        {
                            isActive = false;
                            $( this ).text( options.offText );
                            box.css(
                                {
                                    top: box.initialTop
                                }
                            );    
                            $.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 = ani();
                
                // 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 = ani();
                
                // 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 );