import Foundation

public struct Stack<Element>
{
    private var storage: [Element]

    public init()
    {
        self.storage = [Element]()
    }

    public mutating func push(_ element: Element) -> Void
    {
        self.storage.insert(element, at: 0)
    }

    public mutating func pop() -> Element?
    {
        return self.storage.removeFirst()
    }

    public func whosOnTop() -> Element?
    {
        return self.storage.first
    }
}

//
// TEST
//

var stack = Stack<Int>()

stack.push(1)
stack.push(2)
stack.push(3)
stack.push(4)
stack.push(5)

if let top = stack.whosOnTop()
{
    print("Top \(top)")
}

print(stack)

if let fuera = stack.pop()
{
    print("Fuera: \(fuera)")
}

print(stack)

stack.push(5)
print(stack)