/**
* 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);