(function($) {
  var has_VML, create_canvas_for, add_shape_to, clear_canvas, shape_from_area,
    canvas_style, fader, hex_to_decimal, css3color, is_image_loaded;
  has_VML = document.namespaces;
  has_canvas = document.createElement('canvas');
  has_canvas = has_canvas && has_canvas.getContext;
  
  if(!(has_canvas || has_VML)) {
    $.fn.maphilight = function() { return this; };
    return;
  }
  
  if(has_canvas) {
    fader = function(element, opacity, interval) {
      if(opacity <= 1) {
        element.style.opacity = opacity;
        window.setTimeout(fader, 10, element, opacity + 0.1, 10);
      }
    };
    
    hex_to_decimal = function(hex) {
      return Math.max(0, Math.min(parseInt(hex, 16), 255));
    };
    css3color = function(color, opacity) {
      return 'rgba('+hex_to_decimal(color.substr(0,2))+','+hex_to_decimal(color.substr(2,2))+','+hex_to_decimal(color.substr(4,2))+','+opacity+')';
    };
    create_canvas_for = function(img) {
      var c = $('<canvas style="width:'+img.width+'px;height:'+img.height+'px;"></canvas>').get(0);
      c.getContext("2d").clearRect(0, 0, c.width, c.height);
      return c;
    };
    add_shape_to = function(canvas, shape, coords, options) {
      var i, context = canvas.getContext('2d');
      context.beginPath();
      if(shape == 'rect') {
        context.rect(coords[0], coords[1], coords[2] - coords[0], coords[3] - coords[1]);
      } else if(shape == 'poly') {
        context.moveTo(coords[0], coords[1]);
        for(i=2; i < coords.length; i+=2) {
          context.lineTo(coords[i], coords[i+1]);
        }
      } else if(shape == 'circ') {
        context.arc(coords[0], coords[1], coords[2], 0, Math.PI * 2, false);
      }
      context.closePath();
      if(options.fill) {
        context.fillStyle = css3color(options.fillColor, options.fillOpacity);
        context.fill();
      }
      if(options.stroke) {
        context.strokeStyle = css3color(options.strokeColor, options.strokeOpacity);
        context.lineWidth = options.strokeWidth;
        context.stroke();
      }
      if(options.fade) {
        fader(canvas, 0);
      }
    };
    clear_canvas = function(canvas, area) {
      canvas.getContext('2d').clearRect(0, 0, canvas.width,canvas.height);
    };
  } else {
    // document.createStyleSheet().addRule("v\\:*", "behavior: url(#default#VML); antialias: true;"); 
    //    document.namespaces.add("v", "urn:schemas-microsoft-com:vml"); 
    document.namespaces.add("v", "urn:schemas-microsoft-com:vml"); 
    var style = document.createStyleSheet();
    var shapes = ['shape','rect', 'oval', 'circ', 'fill', 'stroke', 'imagedata', 'group','textbox'];  
    $.each(shapes,
        function()
        {
            style.addRule('v\\:' + this, "behavior: url(#default#VML); antialias:true");
        }
    );
    
    create_canvas_for = function(img) {
      return $('<var style="zoom:1;overflow:hidden;display:block;width:'+img.width+'px;height:'+img.height+'px;"></var>').get(0);
    };
    add_shape_to = function(canvas, shape, coords, options) {
      var fill, stroke, opacity, e;
      fill = '<v:fill color="#'+options.fillColor+'" opacity="'+(options.fill ? options.fillOpacity : 0)+'" />';
      stroke = (options.stroke ? 'strokeweight="'+options.strokeWidth+'" stroked="t" strokecolor="#'+options.strokeColor+'"' : 'stroked="f"');
      opacity = '<v:stroke opacity="'+options.strokeOpacity+'"/>';
      if(shape == 'rect') {
        e = $('<v:rect filled="t" '+stroke+' style="zoom:1;margin:0;padding:0;display:block;position:absolute;left:'+coords[0]+'px;top:'+coords[1]+'px;width:'+(coords[2] - coords[0])+'px;height:'+(coords[3] - coords[1])+'px;"></v:rect>');
      } else if(shape == 'poly') {
        e = $('<v:shape filled="t" '+stroke+' coordorigin="0,0" coordsize="'+canvas.width+','+canvas.height+'" path="m '+coords[0]+','+coords[1]+' l '+coords.join(',')+' x e" style="zoom:1;margin:0;padding:0;display:block;position:absolute;top:0px;left:0px;width:'+canvas.width+'px;height:'+canvas.height+'px;"></v:shape>');
      } else if(shape == 'circ') {
        e = $('<v:oval filled="t" '+stroke+' style="zoom:1;margin:0;padding:0;display:block;position:absolute;left:'+(coords[0] - coords[2])+'px;top:'+(coords[1] - coords[2])+'px;width:'+(coords[2]*2)+'px;height:'+(coords[2]*2)+'px;"></v:oval>');
      }
      e.get(0).innerHTML = fill+opacity;
      $(canvas).append(e);
    };
    clear_canvas = function(canvas) {
      $(canvas).empty();
    };
  }
  shape_from_area = function(area) {
    var i, coords = area.getAttribute('coords').split(',');
    for (i=0; i < coords.length; i++) { coords[i] = parseFloat(coords[i]); }
    return [area.getAttribute('shape').toLowerCase().substr(0,4), coords];
  };
  
  is_image_loaded = function(img) {
    if(!img.complete) { return false; } // IE
    if(typeof img.naturalWidth != "undefined" && img.naturalWidth == 0) { return false; } // Others
    return true;
  }

  canvas_style = {
    position: 'absolute',
    left: 0,
    top: 0,
    padding: 0,
    border: 0
  };
  
  $.fn.maphilight = function(opts) {
    opts = $.extend({}, $.fn.maphilight.defaults, opts);
    return this.each(function() {
      var img, wrap, options, map, canvas, canvas_always, mouseover;
      img = $(this);
      if(!is_image_loaded(this)) { return window.setTimeout(function() { img.maphilight(opts); }, 200); }
      options = $.metadata ? $.extend({}, opts, img.metadata()) : opts;
      map = $('map[name="'+img.attr('usemap').substr(1)+'"]');
      if(!(img.is('img') && img.attr('usemap') && map.size() > 0 && !img.hasClass('maphilighted'))) { return; }
      wrap = $('<div>').css({display:'block',background:'url('+this.src+')',position:'relative',padding:0,width:this.width,height:this.height});
      img.before(wrap).css('opacity', 0).css(canvas_style).remove();
      if($.browser.msie) { img.css('filter', 'Alpha(opacity=0)'); }
      wrap.append(img);
      
      canvas = create_canvas_for(this);
      $(canvas).css(canvas_style);
      canvas.height = this.height;
      canvas.width = this.width;
      
      mouseover = function(e) {
        var shape, area_options;
        area_options = $.metadata ? $.extend({}, options, $(this).metadata()) : options;
        if(!area_options.alwaysOn) {
          shape = shape_from_area(this);
          add_shape_to(canvas, shape[0], shape[1], area_options);
        }
      };
      
      if(options.alwaysOn) {
        $(map).find('area[coords]').each(mouseover);
      } else {
        if($.metadata) {
          // If the metadata plugin is present, there may be areas with alwaysOn set.
          // We'll add these to a *second* canvas, which will get around flickering during fading.
          $(map).find('area[coords]').each(function() {
            var shape, area_options;
            area_options = $.metadata ? $.extend({}, options, $(this).metadata()) : options;
            if(area_options.alwaysOn) {
              if(!canvas_always) {
                canvas_always = create_canvas_for(img.get());
                $(canvas_always).css(canvas_style);
                canvas_always.width = img.width();
                canvas_always.height = img.height();
                img.before(canvas_always);
              }
              shape = shape_from_area(this);
              add_shape_to(canvas_always, shape[0], shape[1], area_options);
            }
          })
        }
        $(map).find('area[coords]').mouseover(mouseover).mouseout(function(e) { clear_canvas(canvas); });
      }
      
      img.before(canvas); // if we put this after, the mouseover events wouldn't fire.
      img.addClass('maphilighted');
    });
  };
  $.fn.maphilight.defaults = {
    fill: true,
    fillColor: '000000',
    fillOpacity: 0.2,
    stroke: true,
    strokeColor: 'ff0000',
    strokeOpacity: 1,
    strokeWidth: 1,
    fade: true,
    alwaysOn: false
  };
})(jQuery);