using System.Security.Cryptography;
using Microsoft.Extensions.Options;

namespace lxc_songlist.Services;

public sealed class AdminPasswordService(IOptions<AdminAuthOptions> options)
{
    private const int SaltBytes = 16;
    private const int HashBytes = 32;
    private const int Iterations = 210_000;

    public bool Verify(string password)
    {
        var configuredHash = options.Value.PasswordHash;
        if (!string.IsNullOrWhiteSpace(configuredHash))
        {
            return VerifyHash(password, configuredHash);
        }

        var configuredPassword = options.Value.Password;
        return !string.IsNullOrEmpty(configuredPassword)
            && CryptographicOperations.FixedTimeEquals(
                System.Text.Encoding.UTF8.GetBytes(password),
                System.Text.Encoding.UTF8.GetBytes(configuredPassword));
    }

    public static string CreateHash(string password)
    {
        var salt = RandomNumberGenerator.GetBytes(SaltBytes);
        var hash = Rfc2898DeriveBytes.Pbkdf2(password, salt, Iterations, HashAlgorithmName.SHA256, HashBytes);
        return $"pbkdf2${Iterations}${Convert.ToBase64String(salt)}${Convert.ToBase64String(hash)}";
    }

    private static bool VerifyHash(string password, string storedHash)
    {
        var parts = storedHash.Split('$');
        if (parts.Length != 4 || parts[0] != "pbkdf2" || !int.TryParse(parts[1], out var iterations))
        {
            return false;
        }

        try
        {
            var salt = Convert.FromBase64String(parts[2]);
            var expectedHash = Convert.FromBase64String(parts[3]);
            var actualHash = Rfc2898DeriveBytes.Pbkdf2(password, salt, iterations, HashAlgorithmName.SHA256, expectedHash.Length);
            return CryptographicOperations.FixedTimeEquals(actualHash, expectedHash);
        }
        catch (FormatException)
        {
            return false;
        }
    }
}