using System.Buffers.Binary;
using System.Net;
using AcDream.Core.Net.Cryptography;
using AcDream.Core.Net.Packets;
using AcDream.Core.Net.Transport;

namespace AcDream.Core.Net.Tests.Transport;

/// <summary>
/// Campaign N Slice N6 — the ConnectResponse handshake retransmit.
///
/// <para>
/// Retail: while a connection sits in <c>cs_ConnectionRequestAcked</c>,
/// <c>ClientNet::ProcessConnection @ 0x00545450</c> (case 0 at 0x0054547B)
/// re-sends the ConnectResponse every 0.333333333 s — strictly-greater gate
/// on <c>lastSentHandshake_</c> (mask-0x41 x87 test at 0x0054548C) —
/// through <c>ClientNet::SendConnectAck @ 0x005440F0</c>, which re-stamps
/// the clock (0x00544102) and rebuilds the same cookie packet. The resend
/// stops when the first successfully processed non-ConnectRequest packet
/// promotes the connection to <c>cs_Connected</c>
/// (<c>ClientNet::ProcessPacket @ 0x00545100</c>, the state set at
/// 0x00545160).
/// </para>
///
/// <para>
/// Clocking: the retry cadence rides the TransportClock, so these tests
/// drive it on VIRTUAL time (<c>TransportClockSource</c> +
/// <c>AutoAdvanceOnBlockingReceive</c>); only the Connect deadline is
/// wall-clock. Before N6 the first test hung to that deadline — a lost
/// ConnectResponse was an unconditional Connect failure, and the N5 loss
/// decorator deliberately arms AFTER the handshake window, so nothing
/// covered it.
/// </para>
/// </summary>
public sealed class ConnectResponseRetransmitTests
{
    /// <summary>THE N6 conformance test: the first ConnectResponse datagram
    /// dies on the wire; the 0.333 s retry lands; the session completes.
    /// Exactly one retry — confirmation (the first decoded server packet)
    /// stops the cadence.</summary>
    [Fact]
    public void Connect_FirstConnectResponseDropped_RetryHealsHandshake()
    {
        var fake = new FakeAceTransport
        {
            AutoAdvanceOnBlockingReceive = TimeSpan.FromMilliseconds(200),
        };
        int connectResponsesSent = 0;
        fake.Link.Drop(LinkDirection.ClientToServer, (_, datagram) =>
        {
            if (!IsConnectResponse(datagram))
                return false;
            connectResponsesSent++;
            return connectResponsesSent == 1; // only the FIRST one dies
        });
        int accepted = 0;
        fake.Model.ConnectResponseAccepted += () => accepted++;

        using var session = new WorldSession(
            new IPEndPoint(IPAddress.Loopback, 9000),
            fake);
        session.TransportClockSource =
            (fake.Clock.GetTimestamp, fake.Clock.Frequency);

        session.Connect("testaccount", "testpassword", TimeSpan.FromSeconds(10));

        Assert.Equal(WorldSession.State.InCharacterSelect, session.CurrentState);
        Assert.NotNull(session.Characters);
        // Original + exactly one retry, and none after confirmation (the
        // CharacterList response follows the accepted retry immediately).
        Assert.Equal(2, connectResponsesSent);
        Assert.Equal(1, accepted);
        // The retry arrived while ACE was still AuthConnectResponse — the
        // NetworkManager pre-route accepted it; nothing was state-dropped
        // and no keystream/CRC cost was paid anywhere.
        Assert.Equal(0, fake.Model.StateDropCount);
        Assert.Equal(0, fake.Model.CrcDropCount);
        Assert.Equal(0, fake.Model.DuplicateDropCount);
        Assert.Equal(256, fake.Model.Crypto.Headroom);
    }

    /// <summary>A clean handshake sends exactly ONE ConnectResponse: with
    /// the virtual clock frozen (no auto-advance) the strict 0.333 s gate
    /// can never open, and confirmation lands on the first pump.</summary>
    [Fact]
    public void Connect_CleanHandshake_SendsExactlyOneConnectResponse()
    {
        var fake = new FakeAceTransport();
        int connectResponsesSent = 0;
        fake.Link.Drop(LinkDirection.ClientToServer, (_, datagram) =>
        {
            if (IsConnectResponse(datagram))
                connectResponsesSent++;
            return false; // tap only
        });

        using var session = new WorldSession(
            new IPEndPoint(IPAddress.Loopback, 9000),
            fake);
        session.TransportClockSource =
            (fake.Clock.GetTimestamp, fake.Clock.Frequency);

        session.Connect("testaccount", "testpassword", TimeSpan.FromSeconds(10));

        Assert.NotNull(session.Characters);
        Assert.Equal(1, connectResponsesSent);
        Assert.Equal(0, fake.Model.StateDropCount);
    }

    /// <summary>
    /// The duplicate-in-flight scenario: ACE accepted the ConnectResponse
    /// but its S2C responses died, so the unconfirmed client keeps
    /// retrying. Every duplicate lands harmlessly (ACE's
    /// <c>Session.CheckState</c> clause 2 drops it pre-CRC at zero
    /// keystream cost), and the dropped responses heal through the normal
    /// N2/N4 gap-walk → NAK → cached-retransmit path once ACE's 2 s ack
    /// reveals the gap.
    /// </summary>
    [Fact]
    public void Connect_ServerResponsesLost_RetriesDropHarmlessly_SessionHeals()
    {
        var fake = new FakeAceTransport
        {
            AutoAdvanceOnBlockingReceive = TimeSpan.FromMilliseconds(200),
        };
        // S2C transmit index 0 is the ConnectRequest; indices 1 and 2 are
        // the TimeSync + CharacterList responses to the accepted
        // ConnectResponse. Drop both responses.
        fake.Link.DropAt(LinkDirection.ServerToClient, 1);
        fake.Link.DropAt(LinkDirection.ServerToClient, 2);
        int connectResponsesSent = 0;
        fake.Link.Drop(LinkDirection.ClientToServer, (_, datagram) =>
        {
            if (IsConnectResponse(datagram))
                connectResponsesSent++;
            return false; // tap only
        });
        int accepted = 0;
        fake.Model.ConnectResponseAccepted += () => accepted++;

        using var session = new WorldSession(
            new IPEndPoint(IPAddress.Loopback, 9000),
            fake);
        session.TransportClockSource =
            (fake.Clock.GetTimestamp, fake.Clock.Frequency);

        session.Connect("testaccount", "testpassword", TimeSpan.FromSeconds(10));

        Assert.NotNull(session.Characters);
        // The first ConnectResponse was accepted; at least one retry went
        // out while the client sat unconfirmed, and every one of them was
        // state-dropped by the model without side effects.
        Assert.Equal(1, accepted);
        Assert.True(connectResponsesSent >= 2,
            $"expected retries, saw {connectResponsesSent}");
        Assert.True(fake.Model.StateDropCount >= 1,
            $"expected CheckState drops, saw {fake.Model.StateDropCount}");
        Assert.Equal(0, fake.Model.CrcDropCount);
        Assert.Equal(0, fake.Model.DuplicateDropCount);
        // The dropped TimeSync/CharacterList healed via the client NAK →
        // ACE cached-retransmit path, with the parked-key discipline intact.
        Assert.True(session.Transport!.Stats.NaksSent >= 1);
        Assert.True(session.Transport.Stats.KeysParked >= 2);
        Assert.Equal(0, session.Transport.Stats.ChecksumFailures);
        Assert.Equal(256, fake.Model.Crypto.Headroom);
    }

    /// <summary>Model-level pin of the ACE-safety claim: a duplicate
    /// ConnectResponse AFTER acceptance is dropped by CheckState clause 2
    /// (Session.cs:98-99 / NetworkManager.cs:60-66) before CRC — harmless,
    /// stateless, zero keystream cost.</summary>
    [Fact]
    public void AceModel_DuplicateConnectResponse_AfterAcceptance_DropsViaCheckState()
    {
        var clock = new VirtualClock();
        var model = new AceSessionModel(
            clock,
            FakeAceTransport.DefaultClientSeed,
            FakeAceTransport.DefaultServerSeed,
            FakeAceTransport.DefaultClientId,
            FakeAceTransport.DefaultCookie);
        int accepted = 0;
        model.ConnectResponseAccepted += () => accepted++;

        byte[] cookieBody = new byte[8];
        BinaryPrimitives.WriteUInt64LittleEndian(
            cookieBody, FakeAceTransport.DefaultCookie);
        byte[] connectResponse = PacketCodec.Encode(
            new PacketHeader
            {
                Sequence = 1,
                Flags = PacketHeaderFlags.ConnectResponse,
                Id = 0,
            },
            cookieBody,
            null);

        // AuthenticationHandler moves the session to AuthConnectResponse
        // when the ConnectRequest goes out.
        model.SendConnectRequest();
        Assert.Equal(AceSessionState.AuthConnectResponse, model.State);

        model.Receive(connectResponse);
        Assert.Equal(AceSessionState.AuthConnected, model.State);
        Assert.Equal(1, accepted);
        Assert.Equal(0, model.StateDropCount);

        // The duplicate: CheckState clause 2 drops it pre-CRC.
        model.Receive(connectResponse);
        Assert.Equal(AceSessionState.AuthConnected, model.State);
        Assert.Equal(1, accepted);
        Assert.Equal(1, model.StateDropCount);
        Assert.Equal(0, model.CrcDropCount);
        Assert.Equal(0, model.DuplicateDropCount);
        Assert.Equal(256, model.Crypto.Headroom);
    }

    private static bool IsConnectResponse(byte[] datagram) =>
        datagram.Length >= PacketHeader.Size
        && (BinaryPrimitives.ReadUInt32LittleEndian(datagram.AsSpan(4))
            & (uint)PacketHeaderFlags.ConnectResponse) != 0;
}

/// <summary>
/// Campaign N Slice N6 — the transport end of the fragment-assembler
/// eviction: <see cref="ReliableTransport.Sweep"/> runs
/// <see cref="FragmentAssembler.SweepExpired"/> on retail's 5 s flush
/// cadence (<c>Indicator::FlushTimedOutEphInfo @ 0x0054A3D0</c>).
/// </summary>
public sealed class ReliableTransportAssemblerSweepTests
{
    [Fact]
    public void Sweep_EvictsAgedPartial_KeepsFreshOne()
    {
        var clock = new VirtualClock();
        var assembler = new FragmentAssembler(() => clock.Seconds);
        var transport = new ReliableTransport(
            MakeIsaac(0x11AA22BBu),
            MakeIsaac(0x33CC44DDu),
            0x1234,
            1,
            _ => { },
            new TransportClock(clock.GetTimestamp, clock.Frequency),
            assembler: assembler);

        // Park a partial at t=0.
        IngestPartial(assembler, sequence: 10);
        Assert.Equal(1, assembler.PartialCount);

        // Well under the TTL: sweeps run (5 s cadence) but evict nothing.
        clock.Advance(TimeSpan.FromSeconds(30));
        transport.Sweep();
        Assert.Equal(1, assembler.PartialCount);

        // Park a second partial at t=58, then cross the first one's TTL.
        clock.Advance(TimeSpan.FromSeconds(28));
        IngestPartial(assembler, sequence: 11);
        clock.Advance(TimeSpan.FromSeconds(3.5)); // t = 61.5
        transport.Sweep();

        Assert.Equal(1, assembler.PartialCount); // 10 evicted, 11 kept
        transport.Dispose();
    }

    private static void IngestPartial(FragmentAssembler assembler, uint sequence)
    {
        var header = new MessageFragmentHeader
        {
            Sequence = sequence,
            Id = 0x80000000u,
            Count = 2,
            Index = 0,
            TotalSize = (ushort)(MessageFragmentHeader.Size + 1),
            Queue = 7,
        };
        byte[] payload = { 0x42 };
        Assert.False(assembler.TryIngest(
            new BorrowedMessageFragment(header, payload),
            out _,
            out _));
    }

    private static IsaacRandom MakeIsaac(uint seed)
    {
        Span<byte> seedBytes = stackalloc byte[4];
        BinaryPrimitives.WriteUInt32LittleEndian(seedBytes, seed);
        return new IsaacRandom(seedBytes);
    }
}