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

namespace API.Services;

public class TokenService : ITokenService
{
    private readonly byte[] _secretKey;

    public TokenService(IConfiguration? configuration = null)
    {
        var secret = configuration?["Jwt:Secret"] ?? "ChronoCCG_Super_Secret_Key_For_Jwt_Authentication_2026_Long_Key!";
        _secretKey = Encoding.UTF8.GetBytes(secret);
    }

    public string GenerateToken(string username)
    {
        var payload = new TokenPayload
        {
            Username = username,
            ExpiresAt = DateTimeOffset.UtcNow.AddDays(7).ToUnixTimeSeconds()
        };
        var json = JsonSerializer.Serialize(payload);
        var payloadBytes = Encoding.UTF8.GetBytes(json);
        var payloadBase64 = Convert.ToBase64String(payloadBytes);

        using var hmac = new HMACSHA256(_secretKey);
        var sigBytes = hmac.ComputeHash(Encoding.UTF8.GetBytes(payloadBase64));
        var sigBase64 = Convert.ToBase64String(sigBytes);

        return $"{payloadBase64}.{sigBase64}";
    }

    public string? ValidateToken(string? token)
    {
        if (string.IsNullOrWhiteSpace(token)) return null;

        var parts = token.Split('.');
        if (parts.Length != 2) return null;

        var payloadBase64 = parts[0];
        var sigBase64 = parts[1];

        using var hmac = new HMACSHA256(_secretKey);
        var expectedSigBytes = hmac.ComputeHash(Encoding.UTF8.GetBytes(payloadBase64));
        var expectedSigBase64 = Convert.ToBase64String(expectedSigBytes);

        if (sigBase64 != expectedSigBase64) return null;

        try
        {
            var payloadBytes = Convert.FromBase64String(payloadBase64);
            var json = Encoding.UTF8.GetString(payloadBytes);
            var payload = JsonSerializer.Deserialize<TokenPayload>(json);
            if (payload == null || string.IsNullOrWhiteSpace(payload.Username)) return null;

            if (DateTimeOffset.UtcNow.ToUnixTimeSeconds() > payload.ExpiresAt) return null;

            return payload.Username;
        }
        catch
        {
            return null;
        }
    }

    private class TokenPayload
    {
        public string Username { get; set; } = string.Empty;
        public long ExpiresAt { get; set; }
    }
}