using System.Security.Cryptography;
using System.Text;

namespace Service.Implement
{
    /// <summary>
    /// 密码哈希工具（PBKDF2-SHA256，格式 salt$hash，盐随机 16 字节）
    /// </summary>
    public static class PasswordHelper
    {
        private const int Iterations = 10_000;
        private const int SaltSize = 16;
        private const int HashSize = 32;

        /// <summary>生成密码哈希（salt$hash）</summary>
        public static string Hash(string password)
        {
            var salt = RandomNumberGenerator.GetBytes(SaltSize);
            var hash = Rfc2898DeriveBytes.Pbkdf2(password, salt, Iterations, HashAlgorithmName.SHA256, HashSize);
            return $"{Convert.ToHexString(salt)}${Convert.ToHexString(hash)}";
        }

        /// <summary>校验密码是否匹配</summary>
        public static bool Verify(string password, string? stored)
        {
            if (string.IsNullOrWhiteSpace(stored)) return false;
            var parts = stored.Split('$');
            if (parts.Length != 2) return false;
            var salt = Convert.FromHexString(parts[0]);
            var expected = Convert.FromHexString(parts[1]);
            var actual = Rfc2898DeriveBytes.Pbkdf2(password, salt, Iterations, HashAlgorithmName.SHA256, expected.Length);
            return CryptographicOperations.FixedTimeEquals(actual, expected);
        }

        /// <summary>生成随机盐字符串（供外部使用）</summary>
        public static string NewSalt()
        {
            var salt = RandomNumberGenerator.GetBytes(SaltSize);
            return Convert.ToHexString(salt).ToLowerInvariant();
        }

        /// <summary>SHA256（供 RefreshToken 等场景）</summary>
        public static string Sha256(string input)
        {
            var bytes = SHA256.HashData(Encoding.UTF8.GetBytes(input));
            return Convert.ToHexString(bytes).ToLowerInvariant();
        }
    }
}