Array Implementation

case class Customer(name: String, private var cash: Int) {
    def buy(price: Int): Unit = {
        if(canBuy(price))
            cash -= price
    }

    def canBuy: Int => Boolean = _ <= cash
}

class Applestore(capacity: Int, itemsCount: Int) {
    private var customersWaiting: Array[Customer] = new Array[Customer](capacity)
    private var price: Int      = 900
    private var serveTime: Int  = 60
    private var pointer: Int    = 0

    def canEnqueue: Boolean = pointer < capacity
    def canServe: Boolean = itemsCount > 0
    def countQueue: Int = pointer
    def timeGetServed(customer: Customer): Int = customersWaiting.indexOf(customer) * 60

    def enqueue(customer: Customer): Unit = {
        if(!canEnqueue)
            return

        customersWaiting(pointer) = customer
        pointer += 1
    }

    def serve: Unit = {
        if(!canServe)
            return

        val customer = customersWaiting.head

        if(customer.canBuy(price))
            customer.buy(price)

        customersWaiting = customersWaiting.tail :+ null
        pointer -= 1
    }
}