interface IElement {
    accept(v: ICarVisitor): void
}

//ConcreteElement
class Engine {
    accept(v: ICarVisitor) {
        v.visitEngine(this)
    }
}

//ConcreteElement
class Wheel {
    private number: number

    constructor(number: number) {
        this.number = number
    }

    getNumber() {
        return this.number;
    }

    accept(v: ICarVisitor) {
        v.visitWheel(this)
    }
}

//ConcreteElement
class Car {
    private items = [ 
        new Engine(), 
        new Wheel(1), new Wheel(2), 
        new Wheel(3), new Wheel(4)]

    accept(v: ICarVisitor) {
        for (let i in this.items) {
            if (this.items.hasOwnProperty(i)) {
                this.items[i].accept(v)
            }
        }
        v.visitCar(this)
    }
}

//Visitor
interface ICarVisitor {
    visitEngine(engine: Engine): void
    visitWheel(wheel: Wheel): void
    visitCar(car: Car): void
}

//ConcreteVisitor
class TestCarVisitor implements ICarVisitor {
    visitEngine(engine: Engine) {
        console.log("test engine")
    }

    visitWheel(wheel: Wheel) {
        console.log("test wheel #" + 
            wheel.getNumber())
    }

    visitCar(car: Car) {
        console.log("test car")       
    }
}

//ConcreteVisitor
class RepairCarVisitor {
    visitEngine(engine: Engine) {
        console.log("repair engine")
    }

    visitWheel(wheel: Wheel) {
        console.log("repair wheel #" +
            wheel.getNumber())
    }

    visitCar(car: Car) {
        console.log("repair car")
    }
}

//Client
let car = new Car()
let v1 = new TestCarVisitor()
let v2 = new RepairCarVisitor()

car.accept(v1)
car.accept(v2)