using System.Net;
using System.Text.Json;

namespace MusicBridge.Agent.Network;

// QR payload contract only. Rendering/scanning and the native client are separate steps.
internal sealed record ConnectionInvitation(int Version, string Endpoint, string CertificateSha256,
    string Code, DateTimeOffset ExpiresAt)
{
    public static ConnectionInvitation Create(Uri endpoint, string fingerprint, PairingWindow window, DateTimeOffset now)
    {
        if (!IsLocalEndpoint(endpoint)) throw new ArgumentException("Нужен HTTPS IPv4-адрес домашней сети без пути и параметров.");
        if (fingerprint.Length != 64 || !fingerprint.All(Uri.IsHexDigit)) throw new ArgumentException("Неверный отпечаток сертификата.");
        if (window.Code.Length != 8 || !window.Code.All(char.IsAsciiDigit) || window.ExpiresAt <= now)
            throw new ArgumentException("Окно сопряжения закрыто или код неверен.");
        return new(1, endpoint.GetLeftPart(UriPartial.Authority), fingerprint.ToUpperInvariant(), window.Code, window.ExpiresAt);
    }

    public string ToQrPayload()
    {
        var json = JsonSerializer.SerializeToUtf8Bytes(this, new JsonSerializerOptions(JsonSerializerDefaults.Web));
        var data = Convert.ToBase64String(json).TrimEnd('=').Replace('+', '-').Replace('/', '_');
        return "musicbridge://pair?data=" + data;
    }

    public static bool IsLocalEndpoint(Uri endpoint)
    {
        if (!endpoint.IsAbsoluteUri || endpoint.Scheme != "https" || endpoint.UserInfo != ""
            || endpoint.AbsolutePath != "/" || endpoint.Query != "" || endpoint.Fragment != ""
            || !IPAddress.TryParse(endpoint.Host, out var ip)) return false;
        var bytes = ip.GetAddressBytes();
        return bytes.Length == 4 && (bytes[0] == 10 || bytes[0] == 172 && bytes[1] is >= 16 and <= 31
            || bytes[0] == 192 && bytes[1] == 168);
    }
}