package mqttx

import "sync"

type MessageQueue[T any] struct {
	mu     sync.Mutex
	cond   *sync.Cond
	items  []T
	closed bool
}

func NewMessageQueue[T any]() *MessageQueue[T] {
	q := &MessageQueue[T]{}
	q.cond = sync.NewCond(&q.mu)
	return q
}

func (q *MessageQueue[T]) Push(item T) bool {
	q.mu.Lock()
	defer q.mu.Unlock()
	if q.closed {
		return false
	}
	q.items = append(q.items, item)
	q.cond.Signal()
	return true
}

func (q *MessageQueue[T]) Pop() (T, bool) {
	q.mu.Lock()
	defer q.mu.Unlock()
	for len(q.items) == 0 && !q.closed {
		q.cond.Wait()
	}
	var zero T
	if len(q.items) == 0 {
		return zero, false
	}
	item := q.items[0]
	q.items[0] = zero
	q.items = q.items[1:]
	return item, true
}

func (q *MessageQueue[T]) Drain(max int) []T {
	q.mu.Lock()
	defer q.mu.Unlock()
	if max <= 0 || len(q.items) == 0 {
		return nil
	}
	if max > len(q.items) {
		max = len(q.items)
	}
	items := make([]T, max)
	copy(items, q.items[:max])
	var zero T
	for i := 0; i < max; i++ {
		q.items[i] = zero
	}
	q.items = q.items[max:]
	return items
}

func (q *MessageQueue[T]) Len() int {
	q.mu.Lock()
	defer q.mu.Unlock()
	return len(q.items)
}

func (q *MessageQueue[T]) Close() {
	q.mu.Lock()
	q.closed = true
	q.mu.Unlock()
	q.cond.Broadcast()
}