(function (ko, handlers, unwrap, extend) {
    "use strict";
    extend(handlers, {
        href: {
            update: function (element, valueAccessor) {
                handlers.attr.update(element, function () {
                    return { href: valueAccessor() };
                });
            }
        },
        src: {
            update: function (element, valueAccessor) {
                handlers.attr.update(element, function () {
                    return { src: valueAccessor() };
                });
            }
        },
        hidden: {
            update: function (element, valueAccessor) {
                var value = unwrap(valueAccessor());
                handlers.visible.update(element, function () { return !value; });
            }
        },
        instantValue: {
            init: function (element, valueAccessor, allBindingsAccessor) {
                handlers.value.init(element, valueAccessor,
                    ko.observable(extend(allBindingsAccessor(), {valueUpdate: 'afterkeydown'}))
                    );
            },
            update: handlers.value.update
        },
        toggle: {
            init: function (element, valueAccessor) {
                var value = valueAccessor();
                ko.applyBindingsToNode(element, {
                    click: function () {
                        value(!value());
                    }
                });
            }
        },
        currency: {
            symbol: ko.observable('$'),
            numberToCurrency: function (value, symbol) {
                return symbol + value.toFixed(2).replace(/(\d)(?=(\d{3})+\.)/g, "$1,");
            },
            update: function (element, valueAccessor, allBindingsAccessor) {
                return handlers.text.update(element, function () {
                    var value = +(unwrap(valueAccessor()) || 0),
                        symbol = unwrap(allBindingsAccessor().symbol === undefined
                                    ? allBindingsAccessor().symbol
                                    : handlers.currency.symbol);
                    return handlers.currency.numberToCurrency(value, symbol);
                });
            }
        },
        stopBinding: {
            init: function () {
                return { controlsDescendantBindings: true };
            }
        },
        toJSON: {
            update: function (element, valueAccessor) {
                return handlers.text.update(element, function () {
                    return ko.toJSON(valueAccessor(), null, 2);
                });
            }
        },
        timeAgo: {
            dateToTimeAgo: function (dt) {
                var secs = (((new Date()).getTime() - dt.getTime()) / 1000),
                    days = Math.floor(secs / 86400);

                return days === 0 && (
                    secs < 60 && "just now" ||
                        secs < 120 && "a minute ago" ||
                        secs < 3600 && Math.floor(secs / 60) + " minutes ago" ||
                        secs < 7200 && "an hour ago" ||
                        secs < 86400 && Math.floor(secs / 3600) + " hours ago") ||
                    days === 1 && "yesterday" ||
                    days < 31 && days + " days ago" ||
                    days < 60 && "one month ago" ||
                    days < 365 && Math.ceil(days / 30) + " months ago" ||
                    days < 730 && "one year ago" ||
                    Math.ceil(days / 365) + " years ago";
            },
            update: function (element, valueAccessor) {
                var val = unwrap(valueAccessor()),
                    date = new Date(val), // WARNING: this is not compatibile with IE8
                    timeAgo = handlers.timeAgo.toTimeAgo(date);
                return handlers.html.update(element, function () {
                    return '<time datetime="' + encodeURIComponent(val) + '">' + timeAgo + '</time>';
                });
            }
        }
    });

    ko.virtualElements.allowedBindings.stopBinding = true;
}(ko, ko.bindingHandlers, ko.utils.unwrapObservable, ko.utils.extend));