package stack

type Stack struct {
	*node
}

type node struct {
	value string
	next  *node
}

// New inits a new stack
func New() *Stack {
	return &Stack{}
}

// Push inserts an item to the stack
// Complexity: O(1)
func (s *Stack) Push(v string) {
	s.node = &node{value: v, next: s.node}
}

// Pop removes the the last item from the stack
// Complexity: O(1)
func (s *Stack) Pop() string {
	n := s.node
	v := n.value
	s.node = n.next
	return v
}

// IsEmpty checks the stack's emptiness
// Complexity: O(1)
func (s *Stack) IsEmpty() bool {
	return s.node == nil
}

// Size returns the size of the stack
// Complexity: O(n)
func (s *Stack) Size() uint {
	if s.IsEmpty() {
		return 0
	}
	size := uint(1)
	t := s.node
	for t.next != nil {
		size++
		t = t.next
	}

	return size
}