function OnlineStoreCart() {
    var cache = {}, cacheKey = { cart: 'OnlineStoreCart' },
        gateway = new OnlineStoreCartGateway(), self = this;

    self.addProduct = addProduct;

    cache.get = function (key) {
        var serialized = localStorage.getItem(key);

        if (typeof serialized !== 'string') {
            return undefined;
        }

        try {
            return JSON.parse(serialized);
        } catch(e) {
            console.log(e);
            return serialized || undefined;
        }
    };
    cache.remove = function(key) { localStorage.removeItem(key); };
    cache.set = function (key, value) {
        var serialized = JSON.stringify(value);

        try {
            localStorage.setItem(key, serialized);
        } catch(e) {
            console.log(e);
        }
    };

    function addProduct(productId, quantity) {
        return gateway.addProduct({ productId: productId, quantity: quantity }).done(saveInCache);
    }

    function saveInCache(cart) {
        cache.set(cacheKey.cart, cart);
    }
}