using System;
using System.Collections.Generic;

namespace AX.Common
{
    public class ObjectPool<T>
    {
        private Queue<T> queue;
        private Func<T> creator;
        private Action<T> clearer;

        public int AvailableCount { get { return this.queue.Count; } }

        public ObjectPool(int initialCount, Func<T> creator, Action<T> clearer = null)
        {
            if (initialCount < 0)
                throw new ArgumentOutOfRangeException("initialCount");

            if (creator == null)
                throw new ArgumentNullException("creator");

            this.queue = new Queue<T>(initialCount);

            this.creator = creator;
            this.clearer = clearer;
        }

        /// <summary>
        /// 从对象池获得一个对象实例。
        /// </summary>
        public T Acquire()
        {
            if (queue.Count != 0)
                return queue.Dequeue();

            return creator();
        }

        /// <summary>
        /// 把指定的对象实例归还对象池。
        /// </summary>
        public void Release(T obj)
        {
            if (clearer != null)
                clearer(obj);

            queue.Enqueue(obj);
        }

        public void Clear()
        {
            if (typeof(T) == typeof(IDisposable))
            {
                while (queue.Count != 0)
                {
                    var obj = queue.Dequeue();

                    ((IDisposable)obj).Dispose();
                }
            }
            else
            {
                queue.Clear();
            }

            queue.TrimExcess();
        }
    }
}