/*
Plugin: jQuery Parallax
Version 1.1
Author: Ian Lunn
Author URL: http://www.ianlunn.co.uk/
Plugin URL: http://www.ianlunn.co.uk/plugins/jquery-parallax/

Dual licensed under the MIT and GPL licenses:
http://www.opensource.org/licenses/mit-license.php
http://www.gnu.org/licenses/gpl.html
*/

(function($) {
  $.extend({
    isMobile: function() {
      return window.navigator.userAgent.match(/(iPhone|iPod|iPad)/i) !== null;
    }
  });
  
  $.fn.parallax = function(xpos, adjuster, inertia, outerHeight) {
    //setup defaults if arguments aren't specified
    if (xpos == null) xpos = "50%";
    if (adjuster == null) adjuster = 0;
    if (inertia == null) inertia = 0.1;
    if (outerHeight == null) outerHeight = true;
    
    // No effect for mobile browsers
    if ($.isMobile()) {
      return;
    }
    
    function inView(pos, element) {
      element.each(function() { //for each selector, determine whether it's inview and run the move() function
        var element = $(this);
        var top = element.offset().top;
        
        if (outerHeight) {
          var height = element.outerHeight(true);
        }else{
          var height = element.height();
        }
        
        //above & in view
        if (top + height >= pos && top + height - windowHeight < pos){
          move(pos, height);
        }
        
        //full view
        if (top <= pos && top + height >= pos && top - windowHeight < pos && top + height - windowHeight > pos){
          move(pos, height);
        }
        
        //below & in view
        if (top + height > pos && top - windowHeight < pos && top > pos){
          move(pos, height);
        }
      });
    }
    
    var $window = $(window);
    var windowHeight = $(window).height();
    var pos = $window.scrollTop(); //position of the scrollbar
    var $this = $(this);
    
    var height = outerHeight ? $this.outerHeight(true) : $this.height();
    $this.css({ backgroundPosition: newPos(xpos, height, pos, adjuster, inertia) });
    
    function newPos(xpos, height, scrollPos, adjuster, inertia) {
      return xpos + " " + Math.round(-(height + scrollPos - adjuster) * inertia) + "px";
    }
    
    //function to be called whenever the window is scrolled or resized
    function move(pos, height) { 
        $this.css({ backgroundPosition: newPos(xpos, height, pos, adjuster, inertia) }); 
    }
    
    $window.bind('scroll', function() { //when the user is scrolling...
      var pos = $window.scrollTop(); //position of the scrollbar
      inView(pos, $this);
    });
  };
})(jQuery);