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

namespace SeaHaven.Services.Helpers
{
    /// <summary>
    /// Generation and hashing for invite tokens and email confirmation codes. Raw
    /// values exist only in memory and in the email sent to the invitee.
    /// </summary>
    public static class TeamMemberInviteSecrets
    {
        /// <summary>256 bits from the OS CSPRNG.</summary>
        public const int TokenBytes = 32;

        /// <summary>Upper bound on an accepted token string; a 32-byte base64url token is 43 characters.</summary>
        public const int MaxTokenLength = 128;

        public static string NewToken()
        {
            return Convert.ToBase64String(RandomNumberGenerator.GetBytes(TokenBytes))
                .Replace('+', '-')
                .Replace('/', '_')
                .TrimEnd('=');
        }

        public static string HashToken(string token)
        {
            ArgumentNullException.ThrowIfNull(token);
            return Sha256Hex(token);
        }

        public static string NewCode()
        {
            return RandomNumberGenerator.GetInt32(0, 1_000_000).ToString("D6", CultureInfo.InvariantCulture);
        }

        public static string NewCodeSalt()
        {
            return Convert.ToHexString(RandomNumberGenerator.GetBytes(16)).ToLowerInvariant();
        }

        public static string HashCode(string salt, string code)
        {
            ArgumentNullException.ThrowIfNull(salt);
            ArgumentNullException.ThrowIfNull(code);
            return Sha256Hex(salt + ":" + code);
        }

        public static bool CodeMatches(string salt, string candidate, string expectedHash)
        {
            var actual = Encoding.ASCII.GetBytes(HashCode(salt, candidate));
            var expected = Encoding.ASCII.GetBytes(expectedHash);
            return CryptographicOperations.FixedTimeEquals(actual, expected);
        }

        private static string Sha256Hex(string value)
        {
            return Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(value))).ToLowerInvariant();
        }
    }
}