using System.Net;
using System.Net.Sockets;
using MoShiro.Measurement;
using MoShiro.Protocol;
using MoShiro.TestSupport;

namespace MoShiro.Backend.Tests;

/// <summary>数据面协议拒绝错误首帧、伪造包、重放包和垃圾数据。</summary>
[Trait("Category", "Slow")]
public sealed class AgentDataPlaneTests : IClassFixture<BackendFixture>
{
    private readonly BackendFixture _backend;

    public AgentDataPlaneTests(BackendFixture backend)
    {
        _backend = backend;
    }

    private async Task<(AgentHarness Agent, ProbeSimulator Probe, LineTask Udp)> LineAsync()
    {
        AgentHarness agent = await AgentHarness.StartAsync(_backend);
        await agent.OverrideLineTasksAsync(rateHz: 30);
        ProbeSimulator probe = await agent.ConnectProbeAsync();
        LineTaskSet set = await probe.WaitForTasksAsync(s => s.Tasks.Any(t => t.Kind == "udp_echo" && t.Port == agent.App.QuicPorts[0]));
        return (agent, probe, set.Tasks.Single(t => t.Kind == "udp_echo"));
    }

    [Fact]
    public async Task TcpDataPlane_ClosesConnectionsWithoutAValidFirstFrame()
    {
        (AgentHarness agent, ProbeSimulator probe, _) = await LineAsync();
        await using (agent)
        await using (probe)
        {
            using var client = new TcpClient();
            await client.ConnectAsync(IPAddress.Loopback, agent.App.TcpPorts[0]);
            await client.GetStream().WriteAsync(new byte[TcpWire.AuthBytes]); // 全零：magic 不对
            byte[] buffer = new byte[16];
            Assert.Equal(0, await ReadOrResetAsync(client.GetStream(), buffer)); // 连接被关闭：没有任何字节（Windows 上可能是 RST）
            await BackendFixture.EventuallyAsync(() => Task.FromResult(agent.App.Counters.DroppedInvalid >= 1));
        }
    }

    [Fact]
    public async Task DataPlane_DropsForgedReplayedAndGarbagePackets_WithoutAnswering()
    {
        (AgentHarness agent, ProbeSimulator probe, LineTask udp) = await LineAsync();
        await using (agent)
        await using (probe)
        {
            long before = agent.App.Counters.DroppedInvalid;
            await probe.SendRawUdpAsync([1, 2, 3]);
            await probe.SendRawUdpAsync(new byte[64]);
            await probe.SendForgedEchoAsync(udp, 1);
            await BackendFixture.EventuallyAsync(() => Task.FromResult(agent.App.Counters.DroppedInvalid - before >= 3), because: "garbage and forged packets are counted");

            // 重放：同一个序号发两次，只有第一次被接受
            await probe.SendEchoAsync(udp, 500);
            await BackendFixture.EventuallyAsync(() => Task.FromResult(agent.App.Counters.PacketsOut >= 1));
            long dropped = agent.App.Counters.DroppedInvalid;
            await probe.SendEchoAsync(udp, 500);
            await BackendFixture.EventuallyAsync(() => Task.FromResult(agent.App.Counters.DroppedInvalid > dropped), because: "a replayed packet is dropped");
        }
    }

    private static async Task<int> ReadOrResetAsync(Stream stream, byte[] buffer)
    {
        try
        {
            return await stream.ReadAsync(buffer).AsTask().WaitAsync(TimeSpan.FromSeconds(10));
        }
        catch (IOException)
        {
            return 0;
        }
    }
}