using FileShare_EFCore.Database;
using FileShare_EFCore.Models;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Options;
using System.Security.Cryptography;
using System.Text;

namespace FileShare_API.Authentication
{
    /// <summary>
    /// Refresh Token 服务，负责创建、查找、撤销和轮换 Refresh Token，
    /// Token 原文经 SHA256 哈希后存入数据库以保证安全性。
    /// </summary>
    public sealed class RefreshTokenService(AppDataContext db, IOptions<JwtOptions> options)
    {
        /// <summary>
        /// JWT 配置选项。
        /// </summary>
        private readonly JwtOptions _options = options.Value;

        /// <summary>
        /// 创建一个新的 Refresh Token，生成随机 Token 原文并存储其哈希到数据库。
        /// </summary>
        /// <param name="userId">关联的用户 ID。</param>
        /// <param name="device">创建设备标识（如 User-Agent）。</param>
        /// <param name="ipAddress">客户端 IP 地址。</param>
        /// <param name="cancellationToken">取消令牌。</param>
        /// <returns>包含 Token 原文和实体记录的元组。</returns>
        public async Task<(string Token, ApiRefreshTokenEntity Entity)> CreateAsync(
            int userId,
            string? device,
            string? ipAddress,
            CancellationToken cancellationToken = default)
        {
            var token = Convert.ToBase64String(RandomNumberGenerator.GetBytes(64));
            var entity = new ApiRefreshTokenEntity
            {
                UserId = userId,
                TokenHash = HashToken(token),
                ExpiresAt = DateTime.UtcNow.AddDays(_options.RefreshTokenDays),
                Device = device,
                IpAddress = ipAddress,
            };

            db.ApiRefreshTokens.Add(entity);
            await db.SaveChangesAsync(cancellationToken);
            return (token, entity);
        }

        /// <summary>
        /// 查找有效的 Refresh Token 实体。Token 原文会被哈希后查询数据库，
        /// 仅返回未过期且未被撤销的 Token。
        /// </summary>
        /// <param name="token">Refresh Token 原文。</param>
        /// <param name="cancellationToken">取消令牌。</param>
        /// <returns>有效的 Token 实体；若无效或不存在则返回 null。</returns>
        public async Task<ApiRefreshTokenEntity?> FindActiveAsync(string? token, CancellationToken cancellationToken = default)
        {
            if (string.IsNullOrWhiteSpace(token))
            {
                return null;
            }

            var hash = HashToken(token);
            var entity = await db.ApiRefreshTokens.FirstOrDefaultAsync(x => x.TokenHash == hash, cancellationToken);
            return entity?.IsActive == true ? entity : null;
        }

        /// <summary>
        /// 撤销指定的 Refresh Token，将其 RevokedAt 设为当前时间。
        /// </summary>
        /// <param name="token">要撤销的 Refresh Token 原文。</param>
        /// <param name="cancellationToken">取消令牌。</param>
        public async Task RevokeAsync(string? token, CancellationToken cancellationToken = default)
        {
            var entity = await FindActiveAsync(token, cancellationToken);
            if (entity is null)
            {
                return;
            }

            entity.RevokedAt = DateTime.UtcNow;
            await db.SaveChangesAsync(cancellationToken);
        }

        /// <summary>
        /// 轮换 Refresh Token：撤销旧的并创建新的，将新 Token 的哈希关联到旧记录。
        /// </summary>
        /// <param name="token">旧的 Refresh Token 原文。</param>
        /// <param name="device">当前设备标识。</param>
        /// <param name="ipAddress">当前客户端 IP 地址。</param>
        /// <param name="cancellationToken">取消令牌。</param>
        /// <returns>新的 Token 对；若旧 Token 无效则返回 null。</returns>
        public async Task<(string Token, ApiRefreshTokenEntity Entity)?> RotateAsync(
            string? token,
            string? device,
            string? ipAddress,
            CancellationToken cancellationToken = default)
        {
            var current = await FindActiveAsync(token, cancellationToken);
            if (current is null)
            {
                return null;
            }

            var next = await CreateAsync(current.UserId, device, ipAddress, cancellationToken);
            current.RevokedAt = DateTime.UtcNow;
            current.ReplacedByTokenHash = next.Entity.TokenHash;
            await db.SaveChangesAsync(cancellationToken);
            return next;
        }

        /// <summary>
        /// 对 Token 原文进行 SHA256 哈希，返回十六进制字符串。
        /// </summary>
        /// <param name="token">Token 原文。</param>
        /// <returns>SHA256 哈希后的十六进制字符串。</returns>
        private static string HashToken(string token)
        {
            var bytes = SHA256.HashData(Encoding.UTF8.GetBytes(token));
            return Convert.ToHexString(bytes);
        }
    }
}