using System;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace NewLife.Collections
{
    /// <summary>集群管理</summary>
    /// <typeparam name="TKey"></typeparam>
    /// <typeparam name="TValue"></typeparam>
    public interface ICluster<TKey, TValue>
    {
        /// <summary>最后使用资源</summary>
        KeyValuePair<TKey, TValue> Current { get; }

        /// <summary>资源列表</summary>
        Func<IEnumerable<TKey>> GetItems { get; set; }

        /// <summary>打开</summary>
        Boolean Open();

        /// <summary>关闭</summary>
        /// <param name="reason">关闭原因。便于日志分析</param>
        /// <returns>是否成功</returns>
        Boolean Close(String reason);

        /// <summary>从集群中获取资源</summary>
        /// <returns></returns>
        TValue Get();

        /// <summary>归还</summary>
        /// <param name="value"></param>
        Boolean Put(TValue value);
    }

    /// <summary>集群助手</summary>
    public static class ClusterHelper
    {
        /// <summary>借助集群资源处理事务</summary>
        /// <typeparam name="TKey"></typeparam>
        /// <typeparam name="TValue"></typeparam>
        /// <typeparam name="TResult"></typeparam>
        /// <param name="cluster"></param>
        /// <param name="func"></param>
        /// <returns></returns>
        public static TResult Invoke<TKey, TValue, TResult>(this ICluster<TKey, TValue> cluster, Func<TValue, TResult> func)
        {
            var item = default(TValue);
            try
            {
                item = cluster.Get();
                return func(item);
            }
            finally
            {
                cluster.Put(item);
            }
        }

        /// <summary>借助集群资源处理事务</summary>
        /// <typeparam name="TKey"></typeparam>
        /// <typeparam name="TValue"></typeparam>
        /// <typeparam name="TResult"></typeparam>
        /// <param name="cluster"></param>
        /// <param name="func"></param>
        /// <returns></returns>
        public static async Task<TResult> InvokeAsync<TKey, TValue, TResult>(this ICluster<TKey, TValue> cluster, Func<TValue, Task<TResult>> func)
        {
            var item = default(TValue);
            try
            {
                item = cluster.Get();
                return await func(item).ConfigureAwait(false);
            }
            finally
            {
                cluster.Put(item);
            }
        }
    }
}