package dsUtils

import (
	"io"
	"sync"
)

type IStack[T any] interface {
	Push(item T)
	Get() T
	Len() int
}

// Stack isn't thread safe and suppose to be used only in a single thread
// For multithreaded usage -- use Stack
type Stack[T any] struct {
	IStack[T]
	Buffer []T
}

// NewStack creates a new Stack instance
func NewStack[T any]() *Stack[T] {
	return &Stack[T]{}
}

func (s *Stack[T]) Push(item T) {
	s.Buffer = append(s.Buffer, item)
}

func (s *Stack[T]) Get() (T, error) {
	if len(s.Buffer) == 0 {
		var out T
		return out, io.EOF
	}
	item := s.Buffer[len(s.Buffer)-1]
	s.Buffer = s.Buffer[:len(s.Buffer)-1]
	return item, nil
}

func (s *Stack[T]) Len() int {
	return len(s.Buffer)
}

// StackSync is a Stack but for multi thread usage
type StackSync[T any] struct {
	IStack[T]
	Buffer       []T
	Mu           *sync.Mutex
	NonEmptyCond *sync.Cond
}

func NewStackSync[T any]() *StackSync[T] {
	return &StackSync[T]{
		Mu:           &sync.Mutex{},
		NonEmptyCond: sync.NewCond(&sync.RWMutex{}),
	}
}

func (s *StackSync[T]) Push(item T) {
	s.Mu.Lock()
	s.Buffer = append(s.Buffer, item)
	s.NonEmptyCond.Signal()
	s.Mu.Unlock()
}

func (s *StackSync[T]) Get() T {
	s.Mu.Lock()
	if len(s.Buffer) < 1 {
		s.NonEmptyCond.Wait()
	}
	item := s.Buffer[len(s.Buffer)-1]
	s.Buffer = s.Buffer[:len(s.Buffer)-1]
	s.Mu.Unlock()
	return item
}

func (s *StackSync[T]) Len() int {
	s.Mu.Lock()
	defer s.Mu.Lock()
	return len(s.Buffer)
}