using System.Net.WebSockets;
using Vanguard.Shared.Protocol;

namespace Vanguard.Server.Realtime;

/// <summary>Чтение одного кадра протокола из бинарных сообщений WebSocket.</summary>
internal static class ProtocolFrameReader
{
    public static async Task<ClientFrame?> ReadAsync(WebSocket socket, CancellationToken cancellationToken)
    {
        var buffer = new byte[16 * 1024];
        using var stream = new MemoryStream();

        while (true)
        {
            var result = await socket.ReceiveAsync(buffer.AsMemory(), cancellationToken);

            if (result.MessageType == WebSocketMessageType.Close)
                return null;

            if (result.MessageType != WebSocketMessageType.Binary)
                throw new ProtocolFormatException("Ожидался бинарный кадр.");

            stream.Write(buffer, 0, result.Count);

            if (stream.Length > ProtocolConstants.MaxFrameBytes)
                throw new ProtocolFormatException(
                    $"Кадр больше {ProtocolConstants.MaxFrameBytes} байт.");

            if (result.EndOfMessage)
                break;
        }

        return ProtocolSerializer.DecodeClient(stream.ToArray());
    }
}

/// <summary>Не больше N интентов в секунду с одного соединения.</summary>
internal sealed class IntentRateLimiter
{
    private readonly int _limit;
    private readonly TimeProvider _time;
    private DateTimeOffset _windowStart;
    private int _count;

    public IntentRateLimiter(int limit, TimeProvider time)
    {
        _limit = limit;
        _time = time;
        _windowStart = time.GetUtcNow();
    }

    public bool TryAcquire()
    {
        var now = _time.GetUtcNow();
        if (now - _windowStart >= TimeSpan.FromSeconds(1))
        {
            _windowStart = now;
            _count = 0;
        }

        return ++_count <= _limit;
    }
}