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

namespace HSchool.AppHost.Tests;

/// <summary>
/// Talks to the running server exactly the way the browser client does: binary frames over
/// a WebSocket, plus the HTTP endpoints the dashboard and probes use.
/// </summary>
[Collection(AppHostCollection.Name)]
public class GameServerIntegrationTests(AppHostFixture fixture)
{
    private static readonly TimeSpan DefaultTimeout = TimeSpan.FromSeconds(30);

    private DistributedApplication App => fixture.App;

    [Fact]
    public async Task HealthEndpoint_ReportsHealthy()
    {
        using var client = App.CreateHttpClient("server");

        using var response = await client.GetAsync("/health", TestContext.Current.CancellationToken);

        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
    }

    [Fact]
    public async Task StatusEndpoint_ReportsARunningLoop()
    {
        using var client = App.CreateHttpClient("server");

        using var response = await client.GetAsync("/api/status", TestContext.Current.CancellationToken);
        response.EnsureSuccessStatusCode();

        var status = JsonSerializer.Deserialize<StatusResponse>(
            await response.Content.ReadAsStringAsync(TestContext.Current.CancellationToken),
            JsonSerializerOptions.Web);

        Assert.NotNull(status);
        Assert.Equal(20, status.TickRate);
        Assert.True(status.WorldWidth > 0);

        // The loop runs on its own thread; give it a moment to produce a tick.
        await WaitUntilAsync(
            async () => (await GetStatusAsync(client)).Tick > 0,
            TimeSpan.FromSeconds(5));
    }

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

        var welcome = await ReceiveWelcomeAsync(socket);

        Assert.Equal(ProtocolConstants.Version, welcome.ProtocolVersion);
        Assert.Equal(20, welcome.TickRate);
        Assert.True(welcome.PlayerEntityId > 0);
    }

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

        var entities = await ReceiveSnapshotWithAsync(socket, welcome.PlayerEntityId);

        Assert.Contains(entities, entity => entity.Kind == EntityKind.Obstacle);
    }

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

        var first = await ReceiveSnapshotWithAsync(socket, welcome.PlayerEntityId);
        var startX = first.Single(entity => entity.Id == welcome.PlayerEntityId).X;

        // Hold "right" for a few ticks, draining snapshots so the socket never backs up.
        var sequence = 0u;
        var lastX = startX;
        for (var i = 0; i < 20; i++)
        {
            await SendAsync(socket, buffer =>
                ProtocolCodec.WriteInput(buffer, new ClientInputMessage(++sequence, InputButtons.Right)));

            var entities = await ReceiveSnapshotWithAsync(socket, welcome.PlayerEntityId);
            lastX = entities.Single(entity => entity.Id == welcome.PlayerEntityId).X;
        }

        Assert.True(lastX > startX, $"Player did not move right: {startX} -> {lastX}.");
    }

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

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

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

        Assert.Equal(ClientTime, ProtocolCodec.ReadPong(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), "stale-client")));

        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 async Task<ClientWebSocket> ConnectAsync(string playerName = "integration-test")
    {
        var socket = await ConnectRawAsync();
        await SendAsync(socket, buffer =>
            ProtocolCodec.WriteHello(buffer, new ClientHelloMessage(ProtocolConstants.Version, playerName)));
        return socket;
    }

    private async Task<ClientWebSocket> ConnectRawAsync()
    {
        var http = 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[64];
        var length = write(buffer);

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

    private static async Task<ServerWelcomeMessage> ReceiveWelcomeAsync(WebSocket socket) =>
        ProtocolCodec.ReadWelcome(await ReceiveUntilAsync(socket, MessageType.ServerWelcome));

    private static async Task<EntitySnapshot[]> ReceiveSnapshotAsync(WebSocket socket)
    {
        var frame = await ReceiveUntilAsync(socket, MessageType.ServerSnapshot);

        var entities = new EntitySnapshot[ushort.MaxValue];
        var count = ProtocolCodec.ReadSnapshot(frame, entities, out _);

        return entities[..count];
    }

    /// <summary>
    /// Reads snapshots until the given entity shows up. The very first snapshot after a join can
    /// still describe the tick before the spawn was applied.
    /// </summary>
    private static async Task<EntitySnapshot[]> ReceiveSnapshotWithAsync(WebSocket socket, uint entityId)
    {
        for (var attempt = 0; attempt < 10; attempt++)
        {
            var entities = await ReceiveSnapshotAsync(socket);
            if (Array.Exists(entities, entity => entity.Id == entityId))
            {
                return entities;
            }
        }

        throw new InvalidOperationException($"Entity {entityId} never appeared in a snapshot.");
    }

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

        var buffer = new byte[ProtocolConstants.MaxMessageSize];

        while (true)
        {
            var result = await socket.ReceiveAsync(buffer, timeout.Token);
            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;
            }
        }
    }

    private static async Task<StatusResponse> GetStatusAsync(HttpClient client)
    {
        var json = await client.GetStringAsync("/api/status", TestContext.Current.CancellationToken);
        return JsonSerializer.Deserialize<StatusResponse>(json, JsonSerializerOptions.Web)!;
    }

    private static async Task WaitUntilAsync(Func<Task<bool>> condition, TimeSpan timeout)
    {
        var deadline = DateTime.UtcNow + timeout;

        while (DateTime.UtcNow < deadline)
        {
            if (await condition())
            {
                return;
            }

            await Task.Delay(100, TestContext.Current.CancellationToken);
        }

        Assert.Fail($"Condition was not met within {timeout}.");
    }

    private sealed record StatusResponse(
        uint Tick,
        int TickRate,
        int Players,
        int Connections,
        float WorldWidth,
        float WorldHeight);
}