// Copyright (C) 2019 Storj Labs, Inc.
// See LICENSE for copying information.

package testqueue

import (
	"container/list"
	"sync"

	"storj.io/storj/storage"
)

//Queue is a threadsafe FIFO queue implementing storage.Queue
type Queue struct {
	mu sync.Mutex
	s  *list.List
}

//New returns a queue suitable for testing
func New() *Queue {
	return &Queue{s: list.New(), mu: sync.Mutex{}}
}

//Enqueue add a FIFO element
func (q *Queue) Enqueue(value storage.Value) error {
	q.mu.Lock()
	defer q.mu.Unlock()
	q.s.PushBack(value)
	return nil
}

//Dequeue removes a FIFO element
func (q *Queue) Dequeue() (storage.Value, error) {
	q.mu.Lock()
	defer q.mu.Unlock()
	for q.s.Len() > 0 {
		e := q.s.Front() // First element
		q.s.Remove(e)    // Dequeue
		return e.Value.(storage.Value), nil
	}
	return nil, storage.ErrEmptyQueue.New("")
}

//Peekqueue gets upto 'limit' entries from the list queue
func (q *Queue) Peekqueue(limit int) ([]storage.Value, error) {
	q.mu.Lock()
	defer q.mu.Unlock()
	if limit < 0 || limit > storage.LookupLimit {
		limit = storage.LookupLimit
	}
	result := make([]storage.Value, 0)
	for e := q.s.Front(); e != nil; e = e.Next() {
		result = append(result, e.Value.(storage.Value))
		limit--
		if limit <= 0 {
			break
		}
	}
	return result, nil
}

//Close closes the queue
func (q *Queue) Close() error {
	return nil
}