package aoc

type stack[T any] []T

func NewStack[T any](items ...T) *stack[T] {
	s := make(stack[T], len(items))
	copy(s, items)
	return &s
}

// Push adds an element to the top of the stack.
func (s *stack[T]) Push(v T) {
	*s = append(*s, v)
}

// Pop removes the top element from the stack and returns it.
// If the stack is empty, it panics.
func (s *stack[T]) Pop() T {
	if s.IsEmpty() {
		var zero T
		return zero
	}

	v := (*s)[len(*s)-1]
	*s = (*s)[:len(*s)-1]
	return v
}

// Peek returns the top element from the stack without removing it.
// If the stack is empty, it panics.
func (s *stack[T]) Peek() T {
	if s.IsEmpty() {
		var zero T
		return zero
	}

	return (*s)[len(*s)-1]
}	

// Len returns the number of elements in the stack.
func (s *stack[T]) Len() int {
	return len(*s)
}	

// IsEmpty returns true if the stack is empty and false otherwise.
func (s *stack[T]) IsEmpty() bool {
	return s == nil || len(*s) == 0
}

// Clear removes all elements from the stack, returning it to its initial state.
func (s *stack[T]) Clear() {
	*s = (*s)[:0]
}

func (s *stack[T]) Pull() T {
	if s.IsEmpty() {
		var zero T
		return zero
	}
	v := (*s)[0]
	*s = (*s)[1:]
	return v
}