using System.IdentityModel.Tokens.Jwt;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Security;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json.Nodes;
using System.Windows;

namespace BaronSoftware.SSO
{
    internal class SsoClient
    {
        private static readonly HttpClient httpclient = new();

        private BaronSSOOption options;

        private SsoClient() { }

        public static SsoClient Create(BaronSSOOption option)
        {
            SsoClient result = new();
            result.options = option;
            return result;
        }

        /// <summary>
        /// 웹뷰 기반 인증: 로그인 창을 띄워 Authorization Code + PKCE로 토큰을 받아온다. (대화형)
        /// </summary>
        public async Task<TokenResponse> LoginAsync()
        {
            var disc = await GetDiscoveryAsync();
            var verifier = PKCEUtil.NewVerifier();
            var state = PKCEUtil.RandomToken();
            var nonce = PKCEUtil.RandomToken();

            var authorizeUrl =
                $"{disc["authorization_endpoint"]}?client_id={Uri.EscapeDataString(options.ClientId)}" +
                $"&redirect_uri={Uri.EscapeDataString(options.RedirectUri)}" +
                $"&response_type=code" +
                $"&code_challenge={PKCEUtil.Challenge(verifier)}&code_challenge_method=S256" +
                $"&state={state}&nonce={nonce}";

            var window = new LoginWindow(authorizeUrl, options.RedirectUri);
            if (Application.Current?.MainWindow is { } owner && !ReferenceEquals(owner, window))
                window.Owner = owner;

            var redirected = await window.ShowAndGetRedirectAsync();

            var q = PKCEUtil.ParseQuery(redirected);
            if (q.TryGetValue("error", out var error))
                throw new InvalidOperationException($"인증 거부: {error} {q.GetValueOrDefault("error_description")}".Trim());
            if (!q.TryGetValue("state", out var returnedState) || returnedState != state)
                throw new SecurityException("state 불일치 (CSRF 의심) — 로그인을 중단합니다.");
            if (!q.TryGetValue("code", out var code) || string.IsNullOrEmpty(code))
                throw new InvalidOperationException("authorization code를 받지 못했습니다.");

            var tokens = await ExchangeAsync(disc, new Dictionary<string, string>
            {
                ["grant_type"] = "authorization_code",
                ["code"] = code,
                ["redirect_uri"] = options.RedirectUri,
                ["client_id"] = options.ClientId,
                ["code_verifier"] = verifier,
            });

            // nonce 검증 (id_token replay 방지)
            var payload = new JwtSecurityTokenHandler().ReadJwtToken(tokens.IdToken).Payload;
            payload.TryGetValue("nonce", out var nonceClaim);
            if (nonceClaim?.ToString() != nonce)
                throw new SecurityException("nonce 불일치 — id_token이 이 요청에 대한 것이 아닙니다.");

            return tokens;
        }

        /// <summary>
        /// refreshToken 기반 인증: 저장된 refresh_token으로 창 없이(無窓) 토큰을 재발급한다.
        /// </summary>
        public async Task<TokenResponse> LoginAsync(string refreshToken)
        {
            if (string.IsNullOrWhiteSpace(refreshToken))
                return await LoginAsync();

            var disc = await GetDiscoveryAsync();
            return await ExchangeAsync(disc, new Dictionary<string, string>
            {
                ["grant_type"] = "refresh_token",
                ["refresh_token"] = refreshToken,
                ["client_id"] = options.ClientId,
            });
        }

        /// <summary>.well-known/openid-configuration 문서를 1회 로드 후 캐시.</summary>
        public async Task<JsonNode> GetDiscoveryAsync()
        {
            var json = await httpclient.GetStringAsync(GlobalConfigs.SsoDiscoveryUri);
            var discovery = JsonNode.Parse(json) ?? throw new InvalidOperationException("Pasing error");
            return discovery;
        }

        /// <summary>로그인 WebView의 세션 쿠키(SSO 세션)를 삭제한다.</summary>
        public Task ClearWebSessionAsync() => LoginWindow.ClearSessionCookiesAsync();

        /// <summary>
        /// SSO 로그아웃(RP-Initiated Logout): end_session_endpoint로 이동해 Baron SSO 세션을 종료한다.
        /// PostLogoutRedirectUri가 설정돼 있으면 그 주소로의 복귀를 WebView에서 가로채 창을 닫고,
        /// 마지막으로 로컬 WebView 세션 쿠키까지 정리한다.
        /// </summary>
        public async Task LogoutAsync(string idToken)
        {
            try
            {
                var disc = await GetDiscoveryAsync();
                var endSession = disc["end_session_endpoint"]?.ToString();

                // end_session_endpoint와 id_token_hint, 그리고 복귀 주소(PostLogoutRedirectUri)가 모두 있어야
                // 임베디드 WebView에서 깔끔하게 로그아웃 → 복귀를 가로챌 수 있다.
                if (!string.IsNullOrEmpty(endSession)
                    && !string.IsNullOrEmpty(idToken)
                    && !string.IsNullOrWhiteSpace(options.PostLogoutRedirectUri))
                {
                    var url =
                        $"{endSession}?id_token_hint={Uri.EscapeDataString(idToken)}" +
                        $"&post_logout_redirect_uri={Uri.EscapeDataString(options.PostLogoutRedirectUri)}" +
                        $"&state={PKCEUtil.RandomToken()}";

                    var window = new LoginWindow(url, options.PostLogoutRedirectUri);
                    if (Application.Current?.MainWindow is { } owner && !ReferenceEquals(owner, window))
                        window.Owner = owner;

                    try
                    {
                        await window.ShowAndGetRedirectAsync();
                    }
                    catch (OperationCanceledException)
                    {
                        // 사용자가 로그아웃 창을 닫아도 로컬 정리는 계속 진행한다.
                    }
                }
            }
            catch
            {
                // end_session 호출 실패(네트워크/디스커버리 등)해도 로컬 쿠키 정리는 시도한다.
            }
            finally
            {
                await ClearWebSessionAsync();
            }
        }

        /// <summary>access_token으로 userinfo 호출 (granted scope에 따른 프로필/소속 클레임).</summary>
        public async Task<string> GetUserInfoAsync(string accessToken)
        {
            var disc = await GetDiscoveryAsync();
            var endpoint = disc["userinfo_endpoint"]?.ToString()
                           ?? throw new InvalidOperationException("discovery hasn't userinfo_endpoint.");

            using var req = new HttpRequestMessage(HttpMethod.Get, endpoint);
            req.Headers.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);
            using var resp = await httpclient.SendAsync(req);
            var body = await resp.Content.ReadAsStringAsync();
            if (!resp.IsSuccessStatusCode)
                throw new InvalidOperationException($"Failed to call userinfo {(int)resp.StatusCode}: {body}");

            return body;
        }

        private static async Task<TokenResponse> ExchangeAsync(JsonNode disc, Dictionary<string, string> form)
        {
            var tokenEndpoint = disc["token_endpoint"]?.ToString()
                                ?? throw new InvalidOperationException("discovery hasn't userinfo_endpoint.");

            using var resp = await httpclient.PostAsync(tokenEndpoint, new FormUrlEncodedContent(form));
            var body = await resp.Content.ReadAsStringAsync();
            if (!resp.IsSuccessStatusCode)
                throw new InvalidOperationException($"Failed to exchange token {(int)resp.StatusCode}: {body}");

            var j = JsonNode.Parse(body) ?? throw new InvalidOperationException("empty token");

            return new TokenResponse(
                j["id_token"]?.ToString() ?? throw new InvalidOperationException("Response has not id_token."),
                j["access_token"]?.ToString() ?? string.Empty,
                j["refresh_token"]?.ToString(),
                j["expires_in"]?.GetValue<int>() ?? 3600,
                body);
        }
    }
}