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

namespace HttpClientStudy.UnitTest.HttpClients
{
    /// <summary>
    /// 管道构建器
    /// </summary>
    public class HttpMessageHandlerBuilder
    {
        public List<DelegatingHandler> Handlers { get; set; }

        public HttpMessageHandlerBuilder()
        {
            this.Handlers = new List<DelegatingHandler>();
        }

        public HttpMessageHandlerBuilder(List<DelegatingHandler> handlers) : base()
        {
            if (handlers != null)
            {
                this.Handlers = handlers;
            }
        }

        public void AddHttpMessageHandler(DelegatingHandler handler)
        {
            Handlers.Add(handler);
        }

        public void RemoveHttpMessageHandler(DelegatingHandler handler)
        {
            Handlers.Remove(handler);
        }

        public List<DelegatingHandler> FindHttpMessageHandler(DelegatingHandler handler)
        {
            return Handlers.Where(h => h.GetType() == handler.GetType()).ToList();
        }

        ///  <summary>
        ///  根据管道配置：创建一个新HttpClient实例
        ///  </summary>
        public HttpClient Build()
        {
            if (this.Handlers == null || this.Handlers.Count == 0)
            {
                return new HttpClient();
            }

            //默认最终处理器
            HttpMessageHandler defaultLastHandler = new SocketsHttpHandler()
            {
                //自定义配置
                PooledConnectionLifetime = TimeSpan.FromSeconds(120),
            };

            //倒序组装：完成后执行顺序与注册顺序一致
            //拷贝份，省得多次调用有问题

            HttpMessageHandler currentHandler = new SocketsHttpHandler()
            {
                //自定义配置
                PooledConnectionLifetime = TimeSpan.FromSeconds(120),
            };

            var builderHandlers = this.Handlers.ToList<DelegatingHandler>();
            builderHandlers.Reverse();

            if (builderHandlers[0].InnerHandler != null)
            {
                currentHandler = builderHandlers[0].InnerHandler;
            }

            for (int i = 0; i < builderHandlers.Count; i++)
            {
                builderHandlers[i].InnerHandler = currentHandler;
                currentHandler = builderHandlers[i];
            }

            // 利用管道创建HttpClient
            var httpClient = new HttpClient(currentHandler);

            return httpClient;
        }
    }
}