using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using Yh.Platform.Auth;

namespace YhCore.WebApi.Auth
{
    /// <summary>
    /// 轻量 CAS service ticket 校验器（对齐 Java CasServiceTicketValidator，不依赖 CAS 客户端库）。
    /// 调用 CAS 的 /serviceValidate 端点，从响应 XML 中提取 &lt;cas:user&gt;。
    /// </summary>
    public class CasServiceTicketValidator
    {
        private readonly string _casServerUrl;
        private readonly int _timeoutMs;

        public CasServiceTicketValidator(string casServerUrl, int timeoutMs = 5000)
        {
            _casServerUrl = casServerUrl;
            _timeoutMs = timeoutMs > 0 ? timeoutMs : 5000;
        }

        /// <summary>校验 ticket，成功返回登录账号，失败/无效返回 null。</summary>
        public async Task<string> ValidateAsync(string ticket, string service, CancellationToken ct = default)
        {
            if (string.IsNullOrWhiteSpace(_casServerUrl))
            {
                throw new AuthException("未配置 CasServerUrlPrefix（yh:sso:cas-server-url-prefix），无法进行 ticket 校验");
            }
            var base_ = _casServerUrl.EndsWith('/') ? _casServerUrl : _casServerUrl + "/";
            var endpoint = base_ + "serviceValidate"
                + "?ticket=" + Uri.EscapeDataString(ticket ?? "")
                + "&service=" + Uri.EscapeDataString(service ?? "");
            try
            {
                using var handler = new SocketsHttpHandler { ConnectTimeout = TimeSpan.FromMilliseconds(_timeoutMs) };
                using var http = new HttpClient(handler) { Timeout = TimeSpan.FromMilliseconds(_timeoutMs) };
                using var resp = await http.GetAsync(endpoint, ct).ConfigureAwait(false);
                var body = await resp.Content.ReadAsStringAsync(ct).ConfigureAwait(false);
                if (!resp.IsSuccessStatusCode || body == null)
                {
                    return null;
                }
                return ExtractUser(body);
            }
            catch (Exception e) when (e is HttpRequestException or TaskCanceledException)
            {
                throw new AuthException("CAS serviceValidate 请求失败: " + e.Message, e);
            }
        }

        /// <summary>
        /// 从 CAS 响应 XML 提取用户名。
        /// 成功响应形如 &lt;cas:serviceResponse&gt;&lt;cas:authenticationSuccess&gt;&lt;cas:user&gt;NAME&lt;/cas:user&gt;...
        /// </summary>
        public static string ExtractUser(string xml)
        {
            if (string.IsNullOrEmpty(xml))
            {
                return null;
            }
            var start = xml.IndexOf("<cas:user>", StringComparison.Ordinal);
            if (start < 0)
            {
                start = xml.IndexOf("<cas:user ", StringComparison.Ordinal); // 容错带属性
            }
            if (start < 0)
            {
                return null;
            }
            var tagEnd = xml.IndexOf('>', start);
            var end = xml.IndexOf("</cas:user>", tagEnd, StringComparison.Ordinal);
            if (tagEnd < 0 || end < 0)
            {
                return null;
            }
            return xml.Substring(tagEnd + 1, end - tagEnd - 1).Trim();
        }
    }
}