package gtq

import (
	"gopkg.in/eapache/queue.v1"
	"sync"
)

// NewQueue initializes and returns an new Queue.
func NewQueue() (q *Queue) {
	return &Queue{
		queue: queue.New(),
		Done:  NewStat(0),
	}
}

// Queue wraps eapache/queue with locking for thread safety. Also bundles in
// Stats, used by schedulers to help pick tasks to execute.
type Queue struct {
	queue *queue.Queue
	mutex sync.Mutex
	// Stat which tracks task removal rate from the queue.
	Done *Stat
}

// Add puts an element on the end of the queue.
func (q *Queue) Add(task func()) {
	q.mutex.Lock()
	defer q.mutex.Unlock()
	q.queue.Add(task)
}

// Get returns the element at index i in the queue.
// This method accepts both positive and negative index values.
// Index 0 refers to the first element, and index -1 refers to the last.
func (q *Queue) Get(i int) (task func()) {
	q.mutex.Lock()
	defer q.mutex.Unlock()
	if (q.queue.Length() < 1 || i > q.queue.Length()-1) || (i < -1) {
		return nil
	}
	return q.queue.Get(i).(func())
}

// Length returns the number of elements currently stored in the queue.
func (q *Queue) Length() int {
	q.mutex.Lock()
	defer q.mutex.Unlock()
	return q.queue.Length()
}

// Peek returns the element at the head of the queue.
func (q *Queue) Peek() (task func()) {
	q.mutex.Lock()
	defer q.mutex.Unlock()
	if q.Length() < 1 {
		return nil
	}
	return q.queue.Peek().(func())
}

// Remove removes and returns the element from the front of the queue.
func (q *Queue) Remove() (task func()) {
	q.mutex.Lock()
	defer q.mutex.Unlock()
	if q.queue.Length() < 1 {
		return nil
	}
	task = q.queue.Remove().(func())
	q.Done.Add(1)
	return task
}