using System.Collections.Generic;
using AcDream.App.Streaming;
using AcDream.Core.World;
using DatReaderWriter.DBObjs;
using Xunit;

namespace AcDream.Core.Tests.Streaming;

public class StreamingControllerTests
{
    private sealed class FakeStreamer
    {
        public List<uint> Loads { get; } = new();
        public List<uint> Unloads { get; } = new();
        public Queue<LandblockStreamResult> Pending { get; } = new();

        public void EnqueueLoad(uint id) => Loads.Add(id);
        public void EnqueueUnload(uint id) => Unloads.Add(id);
        public IReadOnlyList<LandblockStreamResult> DrainCompletions(int max)
        {
            var batch = new List<LandblockStreamResult>();
            while (batch.Count < max && Pending.Count > 0)
                batch.Add(Pending.Dequeue());
            return batch;
        }
    }

    [Fact]
    public void FirstTick_EnqueuesWholeVisibleWindow()
    {
        var state = new GpuWorldState();
        var fake = new FakeStreamer();
        var controller = new StreamingController(
            enqueueLoad: fake.EnqueueLoad,
            enqueueUnload: fake.EnqueueUnload,
            drainCompletions: fake.DrainCompletions,
            applyTerrain: (_, _) => { },
            state: state,
            radius: 2);

        // Center at (50, 50); no landblocks loaded yet.
        controller.Tick(observerCx: 50, observerCy: 50);

        // 5×5 window = 25 loads enqueued, 0 unloads.
        Assert.Equal(25, fake.Loads.Count);
        Assert.Empty(fake.Unloads);
    }

    [Fact]
    public void SecondTick_SamePosition_EnqueuesNothing()
    {
        var state = new GpuWorldState();
        var fake = new FakeStreamer();
        var controller = new StreamingController(
            fake.EnqueueLoad, fake.EnqueueUnload, fake.DrainCompletions,
            (_, _) => { }, state, radius: 2);

        controller.Tick(50, 50);
        fake.Loads.Clear();

        controller.Tick(50, 50);

        Assert.Empty(fake.Loads);
        Assert.Empty(fake.Unloads);
    }

    [Fact]
    public void DrainingLoadedResult_AddsToState()
    {
        var state = new GpuWorldState();
        var fake = new FakeStreamer();
        var applied = new List<LoadedLandblock>();
        var controller = new StreamingController(
            fake.EnqueueLoad, fake.EnqueueUnload, fake.DrainCompletions,
            (lb, _) => applied.Add(lb), state, radius: 2);

        // Note: LoadedLandblock's actual fields are LandblockId, Heightmap,
        // Entities (positional record). Adjust if the first positional arg
        // name differs.
        var lb = new LoadedLandblock(0x32320FFEu, new LandBlock(), System.Array.Empty<WorldEntity>());
        // A.5 T10-T12 follow-up: use a real empty mesh instance instead of
        // default! so any future test that flows MeshData through the apply
        // callback gets a non-null reference to inspect rather than an NRE.
        var stubMesh = new AcDream.Core.Terrain.LandblockMeshData(
            System.Array.Empty<AcDream.Core.Terrain.TerrainVertex>(),
            System.Array.Empty<uint>());
        fake.Pending.Enqueue(new LandblockStreamResult.Loaded(0x32320FFEu, LandblockStreamTier.Near, lb, stubMesh));

        controller.Tick(50, 50);

        Assert.Single(applied);
        Assert.True(state.IsLoaded(0x32320FFEu));
    }

    [Fact]
    public void DrainingUnloadedResult_RemovesFromState()
    {
        var state = new GpuWorldState();
        var fake = new FakeStreamer();
        var controller = new StreamingController(
            fake.EnqueueLoad, fake.EnqueueUnload, fake.DrainCompletions,
            (_, _) => { }, state, radius: 2);

        var lb = new LoadedLandblock(0x32320FFEu, new LandBlock(), System.Array.Empty<WorldEntity>());
        state.AddLandblock(lb);
        fake.Pending.Enqueue(new LandblockStreamResult.Unloaded(0x32320FFEu));

        controller.Tick(50, 50);

        Assert.False(state.IsLoaded(0x32320FFEu));
    }
}