State pattern implemented in kotlin

a.State.kt

package patterns.head_first

class CoffeeMachine {
    var state: CoffeeMachineState
    val MAX_BEANS_QUANTITY = 100
    val MAX_WATER_QUANTITY = 100
    var beansQuantity = 0
    var waterQuantity = 0
    val offState = Off(this)
    val noIngredients = NoIngredients(this)
    val ready = Ready(this)

    init {
        state = offState
    }

    fun turnOn() = state.turnOn()
    fun fillInBeans(quantity: Int) = state.fillInBeans(quantity)
    fun fillInWater(quantity: Int) = state.fillInWater(quantity)
    fun makeCoffee() = state.makeCoffee()
    fun turnOff() = state.turnOff()
    override fun toString(): String {
        return """COFFEE MACHINE → ${state::class.simpleName}
        |   water quantity : $waterQuantity
        |   beans quantity : $beansQuantity
        |""".trimMargin()
    }
}

abstract class CoffeeMachineState(val coffeeMachine: CoffeeMachine) {
    open fun makeCoffee(): Unit = throw UnsupportedOperationException("Operation not supported")
    open fun fillInBeans(quantity: Int): Unit = throw UnsupportedOperationException("Operation not supported")
    open fun fillInWater(quantity: Int): Unit = throw UnsupportedOperationException("Operation not supported")
    open fun turnOn(): Unit = throw UnsupportedOperationException("Operation not supported")
    fun turnOff(): Unit {
        coffeeMachine.state = coffeeMachine.offState
    }
}

class Off(coffeeMachine: CoffeeMachine) : CoffeeMachineState(coffeeMachine) {
    override fun turnOn() {
        coffeeMachine.state = coffeeMachine.noIngredients
        println("Coffee machine turned on")
    }
}

class NoIngredients(coffeeMachine: CoffeeMachine) : CoffeeMachineState(coffeeMachine) {
    override fun fillInBeans(quantity: Int) {
        if ((coffeeMachine.beansQuantity + quantity) <= coffeeMachine.MAX_BEANS_QUANTITY) {
            coffeeMachine.beansQuantity += quantity
            println("Beans filled in")
            if (coffeeMachine.waterQuantity > 0) {
                coffeeMachine.state = coffeeMachine.ready
            }
        }
    }

    override fun fillInWater(quantity: Int) {
        if ((coffeeMachine.waterQuantity + quantity) <= coffeeMachine.MAX_WATER_QUANTITY) {
            coffeeMachine.waterQuantity += quantity
            println("Water filled in")
            if (coffeeMachine.beansQuantity > 0) {
                coffeeMachine.state = coffeeMachine.ready
            }
        }
    }
}

class Ready(coffeeMachine: CoffeeMachine) : CoffeeMachineState(coffeeMachine) {
    override fun makeCoffee() {
        coffeeMachine.beansQuantity--
        coffeeMachine.waterQuantity--
        println("Making coffee ... DONE")
        if (coffeeMachine.beansQuantity == 0 || coffeeMachine.waterQuantity == 0) {
            coffeeMachine.state = coffeeMachine.noIngredients
        }
    }
}

fun main(args: Array<String>) {
    val coffeeMachine = CoffeeMachine()
    coffeeMachine.turnOn()
    println(coffeeMachine)
    coffeeMachine.fillInBeans(2)
    println(coffeeMachine)
    coffeeMachine.fillInWater(2)
    println(coffeeMachine)
    coffeeMachine.makeCoffee()
    println(coffeeMachine)
    coffeeMachine.makeCoffee()
    println(coffeeMachine)
    coffeeMachine.turnOff()
    println(coffeeMachine)
}

b.output

Coffee machine turned on
COFFEE MACHINE → NoIngredients
   water quantity : 0
   beans quantity : 0

Beans filled in
COFFEE MACHINE → NoIngredients
   water quantity : 0
   beans quantity : 2

Water filled in
COFFEE MACHINE → Ready
   water quantity : 2
   beans quantity : 2

Making coffee ... DONE
COFFEE MACHINE → Ready
   water quantity : 1
   beans quantity : 1

Making coffee ... DONE
COFFEE MACHINE → NoIngredients
   water quantity : 0
   beans quantity : 0

COFFEE MACHINE → Off
   water quantity : 0
   beans quantity : 0