var cartModule = (function(postal, $){
    var cartId = 0,
        cartTemplate = "#cart-tmpl",
        cartItemTemplate = "#cart-item-tmpl",
        cartChildrenSelector = "#cart-list",
        wireUpCart = function(cart) {
            postal.subscribe("cart", "init", _.bind(cart.init,cart));

            postal.subscribe("cart", "item.add", function(item) {
                var member = cart.id + "-" + item.id;
                if(cart.items[member]) {
                    cart.items[member].qty++;
                    cart.items[member].notifyOfChange();
                }
                else {
                    cart.items[member] = new CartItem(_.extend(item, { qty: 1, cartId: cart.id }), new CartItemProxy(cartChildrenSelector));
                }
            });
        },
        CartPrototype = {
            init: function() {
                this.items = {};
                this.proxy.render(this);
            }
        },
        Cart = function(domProxy) {
            var self = this;
            self.items = {};
            self.id = cartId;
            self.proxy = domProxy;
            wireUpCart(this);
        },
        CartDomProxyPrototype = {
            render: function(model) {
                $(this.selector).html(_.template($(cartTemplate).html(), model));
            }
        },
        CartDomProxy = function(selector) {
            this.selector = selector;
        },
        CartItemPrototype = {
            notifyOfChange: function() {
                this.proxy.render(this);
            }
        },
        CartItem = function(item, domProxy) {
            this.cartId = item.cartId;
            this.description = item.description;
            this.price = item.price;
            this.productId = item.id;
            this.proxy = domProxy;
            this.qty = item.qty;
            this.notifyOfChange();
        },
        CartItemProxyPrototype = {
            render: function(model) {
                var item = $("#" + model.cartId + "-" + model.productId);
                if(item.length === 0) {
                    $(this.selector).append(_.template($(cartItemTemplate).html(), model));
                }
                else {
                    item.replaceWith(_.template($(cartItemTemplate).html(), model));
                }
            }
        },
        CartItemProxy = function(selector) {
            this.selector = selector;
        };
    Cart.prototype = CartPrototype;
    CartItem.prototype = CartItemPrototype;
    CartItemProxy.prototype = CartItemProxyPrototype;
    CartDomProxy.prototype = CartDomProxyPrototype;

    return {
        start: function(selector) {
            return new Cart(new CartDomProxy(selector));
        }
    }
})(postal, jQuery);