//Example 1
function add(x, y) { return x + y; }
function sub(x, y) { return x - y; }
function mul(x, y) { return x * y; }
function div(x, y) { return x / y; }

const Command = function (execute, undo, value) {
    this.execute = execute;
    this.undo = undo;
    this.value = value;
}

const AddCommand = function (value) {
    return new Command(add, sub, value);
};

const SubCommand = function (value) {
    return new Command(sub, add, value);
};

const MulCommand = function (value) {
    return new Command(mul, div, value);
};

const DivCommand = function (value) {
    return new Command(div, mul, value);
};

const Calculator = function () {
    let current = 0;
    let commands = [];
    let index = 0;

    function action(command) {
        let name = command.execute.toString().substr(9, 3);
        return name.charAt(0).toUpperCase() + name.slice(1);
    }

    return {
        execute: function (command) {
            current = command.execute(current, command.value);
            commands.push(command);
            index++;
            console.log(action(command) + ": " + command.value);
        },

        undo: function () {
            if (index > 0) {
                let command = commands[index - 1];
                current = command.undo(current, command.value);
                index--;
                console.log("Undo " + action(command) + ": " + command.value);
            }
        },
        redo: function () {
            if (index < commands.length) {
                let command = commands[index];
                current = command.execute(current, command.value);
                index++;
                console.log("Redo " + action(command) + ": " + command.value);
            }
        },

        getCurrentValue: function () {
            return current;
        }
    }
}

const calculator = new Calculator();

// issue commands

calculator.execute(new AddCommand(100));
calculator.execute(new SubCommand(24));
calculator.execute(new MulCommand(6));
calculator.execute(new DivCommand(2));
calculator.undo();
calculator.undo();
calculator.redo();
calculator.redo();
calculator.redo();

console.log(`Answer: ${calculator.getCurrentValue()}`);

//Example 2
const carManager = {
    // request information
    requestInfo: function (model, id) {
        return "The information for " + model + " with ID " + id + " is foobar";
    },
    // purchase the car
    buyVehicle: function (model, id) {
        return "You have successfully purchased Item " + id + ", a " + model;
    },
    // arrange a viewing
    arrangeViewing: function (model, id) {
        return "You have successfully booked a viewing of " + model + " ( " + id + " ) ";
    }
};

carManager.execute = function (name) {
    return carManager[name] && carManager[name].apply(carManager, [].slice.call(arguments, 1));
};
console.log(carManager.execute("buyVehicle", "Ford Escort", "453543"));