using System.Net.WebSockets;
using HSchool.Protocol;

namespace HSchool.AppHost.Tests;

/// <summary>
/// Talks to the realtime channel the way the browser does: binary frames over a WebSocket.
/// The clock only moves while a connection has the school open, which is what these assert.
/// </summary>
[Collection(AppHostCollection.Name)]
public class GameSocketTests(AppHostFixture fixture)
{
    private static readonly TimeSpan DefaultTimeout = TimeSpan.FromSeconds(30);
    private static readonly DateTime StartDate = new(2012, 4, 3, 6, 0, 0, DateTimeKind.Utc);

    [Fact]
    public async Task Handshake_AnswersWithAWelcomeFrame()
    {
        using var socket = await ConnectAsync();

        var welcome = ProtocolCodec.ReadWelcome(await ReceiveUntilAsync(socket, MessageType.ServerWelcome));

        Assert.Equal(ProtocolConstants.Version, welcome.ProtocolVersion);
        Assert.Equal(20, welcome.TickRate);
        Assert.Equal(6, welcome.MaxSchools);
    }

    [Fact]
    public async Task ChangingSpeed_DoesNotResumeAPausedSchool()
    {
        using var client = fixture.App.CreateHttpClient("server");
        await SchoolApiTests.ResetAsync(client);
        var school = await SchoolApiTests.CreateAsync(client, "Пауза и скорость", StartDate);

        using var socket = await OpenSchoolAsync(school.Id);
        await ReceiveClockAsync(socket);

        await SendAsync(socket, buffer =>
            ProtocolCodec.WriteSetRunning(buffer, new ClientSetRunningMessage(Running: false)));
        var paused = await ReceiveClockWhereAsync(socket, clock => !clock.Running);

        await SendAsync(socket, buffer =>
            ProtocolCodec.WriteSetSpeed(buffer, new ClientSetSpeedMessage(SpeedIndex: 3)));
        var afterSpeedChange = await ReceiveClockWhereAsync(socket, clock => clock.SpeedIndex == 3);
        var later = await ReceiveClockAfterAsync(socket, TimeSpan.FromSeconds(1));

        Assert.False(afterSpeedChange.Running);
        Assert.False(later.Running);
        Assert.Equal(paused.GameTimeUnixMs, later.GameTimeUnixMs);
    }

    [Fact]
    public async Task NoSchoolOpen_MeansNoClockFramesButTheCalendarKeepsRunning()
    {
        using var client = fixture.App.CreateHttpClient("server");
        await SchoolApiTests.ResetAsync(client);
        var school = await SchoolApiTests.CreateAsync(client, "Живёт сама", StartDate);

        using var socket = await ConnectAsync();
        await ReceiveUntilAsync(socket, MessageType.ServerWelcome);

        // A connection that opened nothing gets no clock frames…
        await Assert.ThrowsAsync<TimeoutException>(() =>
            ReceiveUntilAsync(socket, MessageType.ServerClock, TimeSpan.FromSeconds(1)));

        // …but the school moved on anyway, which is what the menu cards show.
        var reloaded = await FindAsync(client, school.Id);
        Assert.True(reloaded.Running);
        Assert.True(reloaded.GameTime > StartDate, $"The calendar stood still at {reloaded.GameTime:O}.");
    }

    [Fact]
    public async Task OpeningASchool_StreamsItsClock()
    {
        using var client = fixture.App.CreateHttpClient("server");
        await SchoolApiTests.ResetAsync(client);
        var school = await SchoolApiTests.CreateAsync(client, "Ход времени", StartDate);

        using var socket = await OpenSchoolAsync(school.Id);
        var first = await ReceiveClockAsync(socket);

        Assert.Equal(school.Id, first.SchoolId);
        Assert.True(first.Running);
        Assert.Equal(1, first.SpeedIndex);

        // 5 game minutes per real second at ×1, so one second of ticks has to move the calendar.
        var later = await ReceiveClockAfterAsync(socket, TimeSpan.FromSeconds(1));
        var elapsed = ToDate(later) - ToDate(first);

        Assert.InRange(elapsed.TotalMinutes, 3, 8);
    }

    [Fact]
    public async Task Pausing_FreezesTheClock()
    {
        using var client = fixture.App.CreateHttpClient("server");
        await SchoolApiTests.ResetAsync(client);
        var school = await SchoolApiTests.CreateAsync(client, "Пауза", StartDate);

        using var socket = await OpenSchoolAsync(school.Id);
        await ReceiveClockAsync(socket);

        await SendAsync(socket, buffer =>
            ProtocolCodec.WriteSetRunning(buffer, new ClientSetRunningMessage(Running: false)));

        var paused = await ReceiveClockWhereAsync(socket, clock => !clock.Running);
        var later = await ReceiveClockAfterAsync(socket, TimeSpan.FromSeconds(1));

        Assert.False(later.Running);
        Assert.Equal(paused.GameTimeUnixMs, later.GameTimeUnixMs);
    }

    [Fact]
    public async Task SpeedIndex_ChangesHowFastTheCalendarMoves()
    {
        using var client = fixture.App.CreateHttpClient("server");
        await SchoolApiTests.ResetAsync(client);
        var school = await SchoolApiTests.CreateAsync(client, "Быстрая", StartDate);

        using var socket = await OpenSchoolAsync(school.Id);
        await ReceiveClockAsync(socket);

        await SendAsync(socket, buffer =>
            ProtocolCodec.WriteSetSpeed(buffer, new ClientSetSpeedMessage(SpeedIndex: 4)));

        var fast = await ReceiveClockWhereAsync(socket, clock => clock.SpeedIndex == 4);
        var later = await ReceiveClockAfterAsync(socket, TimeSpan.FromSeconds(1));
        var elapsed = ToDate(later) - ToDate(fast);

        // ×4 means 20 game minutes per real second.
        Assert.InRange(elapsed.TotalMinutes, 12, 30);
    }

    [Fact]
    public async Task LeavingASchool_KeepsItsClockRunning()
    {
        using var client = fixture.App.CreateHttpClient("server");
        await SchoolApiTests.ResetAsync(client);
        var school = await SchoolApiTests.CreateAsync(client, "Выход", StartDate);

        using (var socket = await OpenSchoolAsync(school.Id))
        {
            await ReceiveClockAsync(socket);
            await SendAsync(socket, buffer => ProtocolCodec.WriteCloseSchool(buffer));
        }

        var afterLeaving = await FindAsync(client, school.Id);
        await Task.Delay(TimeSpan.FromSeconds(1), TestContext.Current.CancellationToken);
        var later = await FindAsync(client, school.Id);

        Assert.True(later.Running);
        Assert.True(later.GameTime > afterLeaving.GameTime, "The calendar stopped when the client left.");
    }

    [Fact]
    public async Task APausedSchool_StaysPausedAfterLeaving()
    {
        using var client = fixture.App.CreateHttpClient("server");
        await SchoolApiTests.ResetAsync(client);
        var school = await SchoolApiTests.CreateAsync(client, "Оставлена на паузе", StartDate);

        using (var socket = await OpenSchoolAsync(school.Id))
        {
            await ReceiveClockAsync(socket);
            await SendAsync(socket, buffer =>
                ProtocolCodec.WriteSetRunning(buffer, new ClientSetRunningMessage(Running: false)));
            await ReceiveClockWhereAsync(socket, clock => !clock.Running);
            await SendAsync(socket, buffer => ProtocolCodec.WriteCloseSchool(buffer));
        }

        var afterLeaving = await FindAsync(client, school.Id);
        await Task.Delay(TimeSpan.FromSeconds(1), TestContext.Current.CancellationToken);
        var later = await FindAsync(client, school.Id);

        Assert.False(later.Running);
        Assert.Equal(afterLeaving.GameTime, later.GameTime);
    }

    [Fact]
    public async Task DeletingTheOpenSchool_TellsTheClient()
    {
        using var client = fixture.App.CreateHttpClient("server");
        await SchoolApiTests.ResetAsync(client);
        var school = await SchoolApiTests.CreateAsync(client, "Исчезнет", StartDate);

        using var socket = await OpenSchoolAsync(school.Id);
        await ReceiveClockAsync(socket);

        using var deleted = await client.DeleteAsync($"/api/schools/{school.Id}", TestContext.Current.CancellationToken);
        deleted.EnsureSuccessStatusCode();

        var gone = ProtocolCodec.ReadSchoolGone(await ReceiveUntilAsync(socket, MessageType.ServerSchoolGone));

        Assert.Equal(school.Id, gone.SchoolId);
    }

    [Fact]
    public async Task OpeningASchoolThatDoesNotExist_IsAnsweredWithSchoolGone()
    {
        using var socket = await ConnectAsync();
        await ReceiveUntilAsync(socket, MessageType.ServerWelcome);

        await SendAsync(socket, buffer =>
            ProtocolCodec.WriteOpenSchool(buffer, new ClientOpenSchoolMessage(999999)));

        var gone = ProtocolCodec.ReadSchoolGone(await ReceiveUntilAsync(socket, MessageType.ServerSchoolGone));

        Assert.Equal(999999, gone.SchoolId);
    }

    [Fact]
    public async Task Ping_IsAnsweredWithTheSameTimestamp()
    {
        using var socket = await ConnectAsync();
        await ReceiveUntilAsync(socket, MessageType.ServerWelcome);

        const long ClientTime = 1_700_000_000_123;
        await SendAsync(socket, buffer => ProtocolCodec.WritePing(buffer, new ClientPingMessage(ClientTime)));

        var pong = ProtocolCodec.ReadPong(await ReceiveUntilAsync(socket, MessageType.ServerPong));

        Assert.Equal(ClientTime, pong.ClientTimeMs);
    }

    [Fact]
    public async Task VersionMismatch_IsRejected()
    {
        using var socket = await ConnectRawAsync();

        await SendAsync(socket, buffer => ProtocolCodec.WriteHello(
            buffer,
            new ClientHelloMessage((byte)(ProtocolConstants.Version + 1))));

        var buffer = new byte[ProtocolConstants.MaxMessageSize];
        var result = await socket.ReceiveAsync(buffer, TestContext.Current.CancellationToken);

        Assert.Equal(WebSocketMessageType.Close, result.MessageType);
        Assert.Equal(WebSocketCloseStatus.ProtocolError, socket.CloseStatus);
    }

    private static DateTime ToDate(ServerClockMessage clock) =>
        DateTimeOffset.FromUnixTimeMilliseconds(clock.GameTimeUnixMs).UtcDateTime;

    private async Task<SchoolApiTests.SchoolResponse> FindAsync(HttpClient client, int schoolId)
    {
        var state = await SchoolApiTests.GetSchoolsAsync(client);
        var school = state.Schools.SingleOrDefault(candidate => candidate.Id == schoolId);

        Assert.NotNull(school);
        return school;
    }

    private async Task<ClientWebSocket> OpenSchoolAsync(int schoolId)
    {
        var socket = await ConnectAsync();
        await ReceiveUntilAsync(socket, MessageType.ServerWelcome);
        await SendAsync(socket, buffer => ProtocolCodec.WriteOpenSchool(buffer, new ClientOpenSchoolMessage(schoolId)));
        return socket;
    }

    private async Task<ClientWebSocket> ConnectAsync()
    {
        var socket = await ConnectRawAsync();
        await SendAsync(socket, buffer =>
            ProtocolCodec.WriteHello(buffer, new ClientHelloMessage(ProtocolConstants.Version)));
        return socket;
    }

    private async Task<ClientWebSocket> ConnectRawAsync()
    {
        var http = fixture.App.GetEndpoint("server", "http");
        var uri = new UriBuilder(http) { Scheme = "ws", Path = "/ws/game" }.Uri;

        var socket = new ClientWebSocket();
        await socket.ConnectAsync(uri, TestContext.Current.CancellationToken).WaitAsync(DefaultTimeout);
        return socket;
    }

    private static async Task SendAsync(WebSocket socket, Func<byte[], int> write)
    {
        var buffer = new byte[ProtocolCodec.MaxFrameSize];
        var length = write(buffer);

        await socket.SendAsync(
            buffer.AsMemory(0, length),
            WebSocketMessageType.Binary,
            endOfMessage: true,
            TestContext.Current.CancellationToken);
    }

    private static async Task<ServerClockMessage> ReceiveClockAsync(WebSocket socket) =>
        ProtocolCodec.ReadClock(await ReceiveUntilAsync(socket, MessageType.ServerClock));

    /// <summary>Drains clock frames until one satisfies <paramref name="predicate"/>.</summary>
    private static async Task<ServerClockMessage> ReceiveClockWhereAsync(
        WebSocket socket,
        Func<ServerClockMessage, bool> predicate)
    {
        for (var attempt = 0; attempt < 40; attempt++)
        {
            var clock = await ReceiveClockAsync(socket);
            if (predicate(clock))
            {
                return clock;
            }
        }

        throw new InvalidOperationException("No clock frame matched within 40 frames.");
    }

    /// <summary>Keeps reading clock frames for <paramref name="duration"/> and returns the last one.</summary>
    private static async Task<ServerClockMessage> ReceiveClockAfterAsync(WebSocket socket, TimeSpan duration)
    {
        var deadline = DateTime.UtcNow + duration;
        var clock = await ReceiveClockAsync(socket);

        while (DateTime.UtcNow < deadline)
        {
            clock = await ReceiveClockAsync(socket);
        }

        return clock;
    }

    /// <summary>Reads frames until one of <paramref name="expected"/> shows up.</summary>
    private static async Task<byte[]> ReceiveUntilAsync(WebSocket socket, MessageType expected, TimeSpan? timeout = null)
    {
        using var cts = CancellationTokenSource.CreateLinkedTokenSource(TestContext.Current.CancellationToken);
        cts.CancelAfter(timeout ?? DefaultTimeout);

        var buffer = new byte[ProtocolConstants.MaxMessageSize];

        while (true)
        {
            WebSocketReceiveResult result;
            try
            {
                result = await socket.ReceiveAsync(buffer, cts.Token);
            }
            catch (OperationCanceledException) when (!TestContext.Current.CancellationToken.IsCancellationRequested)
            {
                throw new TimeoutException($"No {expected} frame arrived within {timeout ?? DefaultTimeout}.");
            }

            if (result.MessageType == WebSocketMessageType.Close)
            {
                throw new InvalidOperationException($"Socket closed while waiting for {expected}: {socket.CloseStatus}.");
            }

            var frame = buffer[..result.Count];
            if (ProtocolCodec.PeekMessageType(frame) == expected)
            {
                return frame;
            }
        }
    }
}