using System.IdentityModel.Tokens.Jwt;
using System.Security.Claims;
using System.Text;
using BCrypt.Net;
using Microsoft.IdentityModel.Tokens;
using TaxBaik.Domain.Entities;
using TaxBaik.Domain.Interfaces;

namespace TaxBaik.Web.Services;

public class AuthService
{
    private readonly IAdminUserRepository _adminUserRepository;
    private readonly ILogger<AuthService> _logger;
    private readonly string _jwtSecretKey;
    private readonly string? _passwordResetToken;
    private readonly int _tokenExpirationMinutes = 480; // 8시간

    public AuthService(IAdminUserRepository adminUserRepository, ILogger<AuthService> logger, IConfiguration configuration)
    {
        _adminUserRepository = adminUserRepository;
        _logger = logger;
        _jwtSecretKey = configuration["Jwt:SecretKey"] ?? throw new InvalidOperationException("Missing 'Jwt:SecretKey' configuration.");
        _passwordResetToken = configuration["Admin:PasswordResetToken"];
    }

    public async Task<string?> AuthenticateAndGenerateTokenAsync(string username, string password)
    {
        if (string.IsNullOrWhiteSpace(username) || string.IsNullOrWhiteSpace(password))
        {
            return null;
        }

        var user = await _adminUserRepository.GetByUsernameAsync(username);
        if (user == null)
        {
            _logger.LogWarning("로그인 시도: 존재하지 않는 사용자 '{Username}'", username);
            return null;
        }

        if (string.IsNullOrWhiteSpace(user.PasswordHash))
        {
            _logger.LogError("로그인 실패: 사용자 '{Username}'의 PasswordHash가 비어 있습니다.", username);
            return null;
        }

        if (!BCrypt.Net.BCrypt.Verify(password, user.PasswordHash))
        {
            _logger.LogWarning("로그인 시도: 잘못된 비밀번호 '{Username}'", username);
            return null;
        }

        _logger.LogInformation("로그인 성공: {Username}", username);
        await _adminUserRepository.UpdateLastLoginAtAsync(user.Id);
        return GenerateJwtToken(user);
    }

    public async Task<bool> ChangePasswordAsync(string username, string currentPassword, string newPassword)
    {
        if (!IsValidPassword(newPassword))
            throw new ArgumentException("새 비밀번호는 12자 이상이어야 합니다.", nameof(newPassword));

        var user = await _adminUserRepository.GetByUsernameAsync(username);
        if (user == null || string.IsNullOrWhiteSpace(user.PasswordHash))
            return false;

        if (!BCrypt.Net.BCrypt.Verify(currentPassword, user.PasswordHash))
            return false;

        await _adminUserRepository.UpdatePasswordHashAsync(user.Id, BCrypt.Net.BCrypt.HashPassword(newPassword));
        _logger.LogInformation("관리자 비밀번호 변경: {Username}", username);
        return true;
    }

    public async Task<bool> ResetPasswordAsync(string username, string newPassword, string resetToken)
    {
        if (string.IsNullOrWhiteSpace(_passwordResetToken))
            throw new InvalidOperationException("Admin:PasswordResetToken is not configured.");

        if (!TimeConstantEquals(resetToken, _passwordResetToken))
            return false;

        if (!IsValidPassword(newPassword))
            throw new ArgumentException("새 비밀번호는 12자 이상이어야 합니다.", nameof(newPassword));

        var user = await _adminUserRepository.GetByUsernameAsync(username);
        if (user == null)
            return false;

        await _adminUserRepository.UpdatePasswordHashAsync(user.Id, BCrypt.Net.BCrypt.HashPassword(newPassword));
        _logger.LogWarning("관리자 비밀번호 재설정 API 사용: {Username}", username);
        return true;
    }

    private string GenerateJwtToken(AdminUser user)
    {
        var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_jwtSecretKey));
        var creds = new SigningCredentials(key, SecurityAlgorithms.HmacSha256);

        var claims = new[]
        {
            new Claim(ClaimTypes.NameIdentifier, user.Id.ToString()),
            new Claim(ClaimTypes.Name, user.Username),
            new Claim("username", user.Username)
        };

        var token = new JwtSecurityToken(
            issuer: "taxbaik-admin",
            audience: "taxbaik-admin-client",
            claims: claims,
            expires: DateTime.UtcNow.AddMinutes(_tokenExpirationMinutes),
            signingCredentials: creds);

        return new JwtSecurityTokenHandler().WriteToken(token);
    }

    public ClaimsPrincipal? ValidateToken(string token)
    {
        try
        {
            var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_jwtSecretKey));
            var handler = new JwtSecurityTokenHandler();
            var principal = handler.ValidateToken(token, new TokenValidationParameters
            {
                ValidateIssuerSigningKey = true,
                IssuerSigningKey = key,
                ValidateIssuer = true,
                ValidIssuer = "taxbaik-admin",
                ValidateAudience = true,
                ValidAudience = "taxbaik-admin-client",
                ValidateLifetime = true,
                ClockSkew = TimeSpan.Zero
            }, out SecurityToken validatedToken);

            return principal;
        }
        catch
        {
            return null;
        }
    }

    private static bool IsValidPassword(string password) => !string.IsNullOrWhiteSpace(password) && password.Length >= 12;

    private static bool TimeConstantEquals(string value, string expected)
    {
        var valueBytes = Encoding.UTF8.GetBytes(value);
        var expectedBytes = Encoding.UTF8.GetBytes(expected);
        return valueBytes.Length == expectedBytes.Length
            && System.Security.Cryptography.CryptographicOperations.FixedTimeEquals(valueBytes, expectedBytes);
    }
}