using System;
using System.Net;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

namespace TapTap.TapDB.Standalone.Internal {
    public class MessageHandler : HttpClientHandler {
        /// <summary>
        /// 最大重试次数
        /// </summary>
        private const int MAX_RETRY_TIMES = 3;

        public MessageHandler() {
            AllowAutoRedirect = false;
            UseCookies = false;
        }

        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) {
            HttpResponseMessage response = null;
            for (int i = 0; i < MAX_RETRY_TIMES; i++) {
                response = await base.SendAsync(request, cancellationToken);
                if (response.IsSuccessStatusCode) {
                    break;
                }

                if ((int)response.StatusCode >= 300 && (int)response.StatusCode <= 399) {
                    var redirectUri = response.Headers.Location;
                    if (null != redirectUri)
                    {
                        request = GenerateNewRequest(request, redirectUri);
                    }
                }

                if (i != MAX_RETRY_TIMES - 1)
                {
                    response.Dispose();    
                }
            }

            return response;
        }
        
        private static HttpRequestMessage GenerateNewRequest(HttpRequestMessage originalRequest, Uri redirectUri)
        {
            if (!redirectUri.IsAbsoluteUri)
            {
                redirectUri = new Uri(originalRequest.RequestUri, redirectUri);
            }
                    
            var newRequest = new HttpRequestMessage(originalRequest.Method, redirectUri)
            {
                Content = originalRequest.Content
            };

            foreach (var header in originalRequest.Headers)
            {
                newRequest.Headers.TryAddWithoutValidation(header.Key, header.Value);
            }

            return newRequest;
        }
    }
}