package validparens

type stack struct {
	store []rune
}

func (s *stack) Push(r rune) {
	s.store = append(s.store, r)
}

func (s *stack) Pop() rune {
	res := s.store[len(s.store)-1]
	s.store = s.store[:len(s.store)-1]
	return res
}

func (s *stack) Length() int {
	return len(s.store)
}

func (s *stack) OnTop(r rune) bool {
	if s.Length() == 0 {
		return false
	}
	return s.store[len(s.store)-1] == r
}

func NewStack() stack {
	store := make([]rune, 0)
	return stack{
		store: store,
	}
}

func isValid(s string) bool {
	history := NewStack()

	for _, r := range s {
		switch r {
		case '{', '[', '(':
			history.Push(r)
		case ')':
			if !history.OnTop('(') {
				return false
			}
			history.Pop()
		case ']':
			if !history.OnTop('[') {
				return false
			}
			history.Pop()
		case '}':
			if !history.OnTop('{') {
				return false
			}
			history.Pop()
		}

	}

	return history.Length() == 0
}

func IsValid(s string) bool {
	return isValid(s)
}