(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 {
        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);