type Item interface{}

// ItemStack the stack of Items
type ItemStack struct {
	items []Item
	lock  *sync.RWMutex
}

// New creates a new ItemStack
func New(len int, cap int) *ItemStack {
	s := ItemStack{items: make([]Item, len, cap),
		lock: &sync.RWMutex{}}
	return &s
}

// Push adds an Item to the top of the stack
func (s *ItemStack) Push(t Item) {
	s.lock.Lock()
	defer s.lock.Unlock()
	s.items = append(s.items, t)
}

// Pop removes an Item from the top of the stack
func (s *ItemStack) Pop() *Item {
	s.lock.Lock()
	defer s.lock.Unlock()
	item := s.items[len(s.items)-1]
	s.items = s.items[0 : len(s.items)-1]
	return &item
}