using System.Threading.Tasks;
using AcDream.App.Streaming;
using AcDream.Core.World;
using DatReaderWriter.DBObjs;
using Xunit;

namespace AcDream.Core.Tests.Streaming;

public class LandblockStreamerTests
{
    private const int SpinTimeoutMs = 2000;
    private const int SpinStepMs = 10;
    private const int SpinMaxIterations = SpinTimeoutMs / SpinStepMs;

    [Fact]
    public async Task Load_FollowedByDrain_ReturnsLoadedRecord()
    {
        var stubLandblock = new LoadedLandblock(
            0xA9B4FFFEu,
            new LandBlock(),
            System.Array.Empty<WorldEntity>());

        using var streamer = new LandblockStreamer(
            loadLandblock: id => id == 0xA9B4FFFEu ? stubLandblock : null);

        streamer.Start();
        streamer.EnqueueLoad(0xA9B4FFFEu);

        // Spin until the worker produces a completion, with a 2s timeout.
        LandblockStreamResult? result = null;
        for (int i = 0; i < SpinMaxIterations && result is null; i++)
        {
            var drained = streamer.DrainCompletions(maxBatchSize: LandblockStreamer.DefaultDrainBatchSize);
            if (drained.Count > 0) result = drained[0];
            else await Task.Delay(SpinStepMs);
        }

        Assert.NotNull(result);
        var loaded = Assert.IsType<LandblockStreamResult.Loaded>(result);
        Assert.Equal(0xA9B4FFFEu, loaded.LandblockId);
        Assert.Same(stubLandblock, loaded.Landblock);
    }

    [Fact]
    public async Task Load_WhenLoaderReturnsNull_ReportsFailed()
    {
        using var streamer = new LandblockStreamer(
            loadLandblock: _ => null);

        streamer.Start();
        streamer.EnqueueLoad(0x12340000u);

        LandblockStreamResult? result = null;
        for (int i = 0; i < SpinMaxIterations && result is null; i++)
        {
            var drained = streamer.DrainCompletions(LandblockStreamer.DefaultDrainBatchSize);
            if (drained.Count > 0) result = drained[0];
            else await Task.Delay(SpinStepMs);
        }

        Assert.NotNull(result);
        Assert.IsType<LandblockStreamResult.Failed>(result);
    }

    [Fact]
    public async Task Load_WhenLoaderThrows_ReportsFailedWithMessage()
    {
        using var streamer = new LandblockStreamer(
            loadLandblock: _ => throw new System.InvalidOperationException("boom"));

        streamer.Start();
        streamer.EnqueueLoad(0x55550000u);

        LandblockStreamResult? result = null;
        for (int i = 0; i < SpinMaxIterations && result is null; i++)
        {
            var drained = streamer.DrainCompletions(LandblockStreamer.DefaultDrainBatchSize);
            if (drained.Count > 0) result = drained[0];
            else await Task.Delay(SpinStepMs);
        }

        var failed = Assert.IsType<LandblockStreamResult.Failed>(result);
        Assert.Contains("boom", failed.Error);
    }

    [Fact]
    public async Task Unload_ProducesUnloadedResult()
    {
        using var streamer = new LandblockStreamer(loadLandblock: _ => null);

        streamer.Start();
        streamer.EnqueueUnload(0xABCD0000u);

        LandblockStreamResult? result = null;
        for (int i = 0; i < SpinMaxIterations && result is null; i++)
        {
            var drained = streamer.DrainCompletions(LandblockStreamer.DefaultDrainBatchSize);
            if (drained.Count > 0) result = drained[0];
            else await Task.Delay(SpinStepMs);
        }

        var unloaded = Assert.IsType<LandblockStreamResult.Unloaded>(result);
        Assert.Equal(0xABCD0000u, unloaded.LandblockId);
    }

    [Fact]
    public void Load_ExecutesLoaderSynchronously_OnCallingThread()
    {
        // Streamer was made synchronous after Phase A.1 visual verification
        // exposed concurrent dat reads as the cause of "ball of spikes"
        // terrain corruption — DatReaderWriter's DatCollection isn't
        // thread-safe and locking around every dat read on every render-
        // thread code path was too invasive. Until Phase A.3 introduces a
        // thread-safe dat wrapper, the load delegate runs on the calling
        // thread and the result is in the outbox by the time EnqueueLoad
        // returns. This test pins that contract.
        int testThreadId = System.Environment.CurrentManagedThreadId;
        int? loaderThreadId = null;
        var stubLandblock = new LoadedLandblock(
            0x77770FFEu,
            new LandBlock(),
            System.Array.Empty<WorldEntity>());

        using var streamer = new LandblockStreamer(loadLandblock: id =>
        {
            loaderThreadId = System.Environment.CurrentManagedThreadId;
            return stubLandblock;
        });

        streamer.Start();
        streamer.EnqueueLoad(0x77770FFEu);

        // Result is already in the outbox — no spinning needed.
        var drained = streamer.DrainCompletions(LandblockStreamer.DefaultDrainBatchSize);

        Assert.Single(drained);
        Assert.IsType<LandblockStreamResult.Loaded>(drained[0]);
        Assert.Equal(testThreadId, loaderThreadId);
    }
}