kontor-test.js

/**
 * Creates a new Cart object, with an optional pricing parameter.
 * @class
 * @param {object} pricing
 */
function Cart(prices){
    this.total = 0,
    this.pricing = {},
    this.contents = {};

    if (prices){
        this.setPricing(prices);
    }
};

Cart.prototype = {
    /**
     * Assign pricing details to a Cart object.
     * @method
     * @param {object} pricing - A map from item_id to a map of
     * {quantity1: price1, quantity2: price2}
     * @returns {object} cart instance
     */
    setPricing: function (prices){
        var self = this;

        for (var item in prices){
            if (!prices.hasOwnProperty(item)) continue;

            // allow shortcut for qty == 1 items
            if (typeof prices[item] == 'number'){
                this.pricing[item] = { 1: prices[item] };
            }
            // copy qty => price pairs
            else if (typeof prices[item] == 'object'){
                var qtyKeys = Object.keys(prices[item]);
                this.pricing[item] = {};
                qtyKeys.forEach(function(key){
                    self.pricing[item][key] = prices[item][key];
                });
            }
            else {
                throw new Error('Unsupported price format');
            }
        }
        return this;
    },

    /**
     * Scan the specified item_id quantity times
     * @param {string} item_id - Unique id of the item to scan
     * @param {integer} quantity - (Optional) number of items, default 1.
     * @returns {object} cart instance
     */
    scan: function(item_id, quantity){
        if (!quantity) quantity = 1;
        if (!item_id || typeof this.pricing[item_id] !== 'object') {
            throw new Error('No pricing data available for ' + item_id +
                            '. Maybe you forgot to setPricing()?');
        }

        if (this.contents[item_id]){
            this.contents[item_id] += quantity;
        }
        else {
            this.contents[item_id] = quantity;
        }
        return this;
    },

    /**
     * Calculate the cart total, applying quantity discounts.
     * Retrieve the result from the .total property.
     * @returns {object} cart instance
     */
    calculateTotal: function(){
        var cumulative = 0;
        for (var item in this.contents){
            cumulative += this.calculateItemTotal(item, this.contents[item]);
        }
        this.total = cumulative;
        return this;
    },

    /**
     * Calculate the line-item total for specified item_id & quantity
     * @returns {number} item total
     */
    calculateItemTotal: function(item_id, qty){
        var itemPricing = this.pricing[item_id],
            qtyKeys = Object.keys(itemPricing).sort().reverse(),
            curQty = qty,
            cumulative = 0;

        for (var i = 0; i < qtyKeys.length;){
            var blockQty = qtyKeys[i];
            if (blockQty > curQty) {
                i++;
                continue;
            }
            cumulative += itemPricing[blockQty];
            curQty -= blockQty;
            if (curQty < blockQty) i++;
        }
        return cumulative;
    }
};


function test(a, b){
    if (a === b){
        console.log("Test PASSED: " + a + " === " + b);
    }
    else {
        console.log("Test FAILED: " + b + " !== " + b);
    }
}

var testPricing = {
    A: { 1: 2, 4: 7},
    B: 12,
    C: { 1: 1.25, 6: 6 },
    D: 0.15
};

var cartA = new Cart(testPricing);
cartA.scan('A')
    .scan('B')
    .scan('C')
    .scan('D')
    .scan('A')
    .scan('B')
    .scan('A', 2)
    .calculateTotal();
test(cartA.total, 32.40);

var cartB = new Cart();
cartB.setPricing(testPricing)
    .scan('C', 7)
    .calculateTotal();
test(cartB.total, 7.25);

var cartC = new Cart(testPricing);
cartC.scan('A')
    .scan('B')
    .scan('C')
    .scan('D')
    .calculateTotal();
test(cartC.total, 15.40);