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

using AuthStudy.Authentication.Basic.Events;

using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using Microsoft.Net.Http.Headers;

namespace AuthStudy.Authentication.Basic
{
    public class BasicAuthenticationHandler : AuthenticationHandler<BasicAuthenticationOptions>
    {
        private readonly UTF8Encoding _utf8ValidatingEncoding = new UTF8Encoding(false, true);

        public BasicAuthenticationHandler
        (
            IOptionsMonitor<BasicAuthenticationOptions> options,
            ILoggerFactory logger,
            UrlEncoder encoder,
            ISystemClock clock
        )
         : base(options, logger, encoder, clock)
        {
        }

        protected new BasicAuthenticationEvents? Events
        {
            get { return (BasicAuthenticationEvents?)base.Events; }
            set { base.Events = value; }
        }

        protected override Task<object> CreateEventsAsync() => Task.FromResult<object>(new BasicAuthenticationEvents());

        protected override async Task<AuthenticateResult> HandleAuthenticateAsync()
        {
            string requestBasicText = GetRequestBasic();

            //认证信息
            var basicInfo = ParseBasicInfo(requestBasicText);
            if (!basicInfo.ParseResult)
            {
                return AuthenticateResult.Fail(basicInfo.Message);
            }

            try
            {
                var validateCredentialsContext = new ValidateCredentialsContext(Context, Scheme, Options)
                {
                    Username = basicInfo.UserName,
                    Password = basicInfo.Password
                };

                if (Events != null)
                {
                    await Events.ValidateCredentials(validateCredentialsContext);
                }


                if (validateCredentialsContext.Result != null && validateCredentialsContext.Result.Succeeded)
                {
                    var ticket = new AuthenticationTicket(validateCredentialsContext.Principal!, Scheme.Name);
                    return AuthenticateResult.Success(ticket);
                }

                if (validateCredentialsContext.Result != null &&
                    validateCredentialsContext.Result.Failure != null)
                {
                    return AuthenticateResult.Fail(validateCredentialsContext.Result.Failure);
                }

                return AuthenticateResult.NoResult();
            }
            catch (Exception ex)
            {
                var authenticationFailedContext = new BasicAuthenticationFailedContext(Context, Scheme, Options)
                {
                    Exception = ex
                };

                if (Events != null)
                {
                    await Events.AuthenticationFailed(authenticationFailedContext).ConfigureAwait(true);
                }

                if (authenticationFailedContext.Result != null)
                {
                    return authenticationFailedContext.Result;
                }

                throw;
            }
        }

        protected override Task HandleChallengeAsync(AuthenticationProperties properties)
        {
            //如果响应已经开始,则忽略
            //比如同时使用其它认证，失败后已经被设置了
            if (Response.HasStarted)
            {
                return Task.CompletedTask;
            }

            if (!Request.IsHttps && !Options.AllowInsecureProtocol)
            {
                const string insecureProtocolMessage = "请求为HTTP，基本身份验证将不响应。";
                Logger.LogInformation(insecureProtocolMessage);
                Response.StatusCode = StatusCodes.Status421MisdirectedRequest;
            }
            else
            {
                Response.StatusCode = 401;
                if (!Options.SuppressWWWAuthenticateHeader)
                {
                    var headerValue = BasicAuthenticationDefaults.AuthenticationScheme + $" realm=\"{Options.Realm}\"";
                    Response.Headers.Append(HeaderNames.WWWAuthenticate, headerValue);
                }
            }

            return Task.CompletedTask;
        }


        private string GetRequestBasic()
        {
            //请求头接收
            string basicText = Request.Headers["Authorization"].ToString();
            if (string.IsNullOrWhiteSpace(basicText))
            {
                basicText = Request.Headers["Authorization"].ToString();
            }

            //URL参数
            if (string.IsNullOrWhiteSpace(basicText))
            {
                basicText = $"{Request.Query["Basic"]}";
            }

            //URL参数
            if (string.IsNullOrWhiteSpace(basicText))
            {
                basicText = $"{Request.Query["User"]}:{Request.Query["Password"]}";
                basicText = basicText.TrimStart(':');
            }

            return basicText;
        }

        private (bool ParseResult, string Message, string UserName, string Password) ParseBasicInfo(string requestBasic)
        {
            (bool ParseResult, string Message, string UserName, string Password) result = (true, "格式错误", "", "");
            if (string.IsNullOrWhiteSpace(requestBasic))
            {
                result.Message = "无认证信息";
                return result;
            }

            requestBasic = requestBasic.Trim();
            if (requestBasic.Equals("Basic", StringComparison.OrdinalIgnoreCase))
            {
                result.Message = "授权方案是Basic，但标头没有内容!";
                return result;
            }

            var basicList = requestBasic.Split(':');
            if (basicList.Length == 2)
            {
                result.ParseResult = true;
                result.Message = "认证信息正确";
                result.UserName = basicList[0];
                result.Password = basicList[1];
                return result;
            }

            requestBasic = requestBasic.Replace("Basic ", "", StringComparison.OrdinalIgnoreCase);

            string decodedCredentials = string.Empty;
            byte[] base64DecodedCredentials;
            try
            {
                base64DecodedCredentials = Convert.FromBase64String(requestBasic);
            }
            catch (FormatException)
            {
                result.ParseResult = false;
                result.Message = "凭据不是Base64格式";
                return result;
            }

            try
            {
                decodedCredentials = _utf8ValidatingEncoding.GetString(base64DecodedCredentials);
            }
            catch (Exception ex)
            {
                result.ParseResult = false;
                result.Message = $"认证信息生成凭据时异常：{ex.Message}";
                return result;
            }

            var list = decodedCredentials.Split(':');
            if (list.Length != 2)
            {
                result.ParseResult = false;
                result.Message = $"凭据无效，缺少分隔符!";
                return result;
            }

            result.ParseResult = true;
            result.Message = "认证信息正确";
            result.UserName = list[0];
            result.Password = list[1];

            return result;
        }
    }
}