// 0
func example(str: String, isAction: Bool = true, action: () -> Void) {
    print("---------\(str), isAction: \(isAction)---------")
    
    if isAction {
        action()
    }
}

// 1
public struct ArrayStack<T> {
    fileprivate var elements = [T]()
    public init() {}
    
    // 초기화시 Stack의 내부 요소들의 타입은 <T>
    public init<S : Sequence>(_ s: S) where S.Iterator.Element == T {
        self.elements = Array(s.reversed())
    }
    
    // 마지막 요소를 삭제하고 꺼낸값을 반환
    mutating public func pop() -> T? {
        return self.elements.popLast()
        
    }
    
    mutating public func push(element: T){
        self.elements.append(element)
    }
    
    // 마지막 요소를 삭제하지 않고 반환
    public func peek() -> T? {
        return self.elements.last
    }
    
    public func isEmpty() -> Bool {
        return self.elements.isEmpty
    }
    
    public var count: Int {
        return self.elements.count
    }
}

// 2
/*
 var stack: ArrayStack<String> = ["1","2"...]
 리터럴 문법이 가능
 */
extension ArrayStack: ExpressibleByArrayLiteral {
    public typealias ArrayLiteralElement = T
    public init(arrayLiteral elements: T...) {
        self.elements = elements
    }
}

// 3
/*
 ArrayStack<String>(elements: []) ArrayStack<Int>(elements: [1, 2, 3, 4, 5]) -> [] [1, 2, 3, 4, 5]
 프린트시 요소들만 볼수있음. 혹은, 다른것으로 변경 가능
 */
extension ArrayStack: CustomStringConvertible, CustomDebugStringConvertible {
    
    public var description: String {
        return self.elements.description
    }
    
    public var debugDescription: String {
        return self.elements.debugDescription
    }
}

// 4
extension ArrayStack: Sequence {
    public func makeIterator() -> AnyIterator<T> {
        return AnyIterator(IndexingIterator(_elements: self.elements.lazy.reversed()))
    }
}

// 5
example(str: "Stack") {
    
    var myStack = ArrayStack<Int>()
    
    myStack.push(element: 5)
    myStack.push(element: 44)
    myStack.push(element: 23)
    
    print(myStack)
    
    var x = myStack.pop()
    x = myStack.pop()
    
    x = myStack.pop()
    x = myStack.pop()
    x = myStack.pop()
    
    print(myStack)
    
    myStack.push(element: 87)
    myStack.push(element: 2)
    myStack.push(element: 9)
    
    print(myStack)
    print(type(of: myStack))
    
    for i in myStack {
        print(i)
    }
    print("my stack is: \(myStack)")
}