package queue

import (
	"context"
	"sync"
)

type Queue struct {
	ch      chan int64
	mu      sync.Mutex
	pending map[int64]struct{}
}

func New(size int) *Queue {
	return &Queue{ch: make(chan int64, size), pending: make(map[int64]struct{})}
}
func (q *Queue) Enqueue(id int64) bool {
	if id <= 0 {
		return false
	}
	q.mu.Lock()
	if _, ok := q.pending[id]; ok {
		q.mu.Unlock()
		return false
	}
	q.pending[id] = struct{}{}
	q.mu.Unlock()
	select {
	case q.ch <- id:
		return true
	default:
		q.mu.Lock()
		delete(q.pending, id)
		q.mu.Unlock()
		return false
	}
}
func (q *Queue) Next(ctx context.Context) (int64, bool) {
	select {
	case <-ctx.Done():
		return 0, false
	case id := <-q.ch:
		return id, true
	}
}
func (q *Queue) Done(id int64) { q.mu.Lock(); delete(q.pending, id); q.mu.Unlock() }
func (q *Queue) Len() int      { return len(q.ch) }