/**
 * 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 );