using OpenTK.Mathematics;
using VoxelEngine.Core;
using VoxelEngine.World;
using VoxelEngine.World.Blocks;
using VoxelEngine.World.Chunk;
using VoxelEngine.World.Persistence;
using VoxelEngine.World.Streaming;
using Xunit;
using VoxelChunk = VoxelEngine.World.Chunk.Chunk;

namespace VoxelEngine.Tests.Streaming;

// Synchronous executor: runs the submitted action on the calling thread.
internal sealed class SynchronousJobExecutor : IJobExecutor
{
    public void Submit(Action work) => work();
}

// Fake renderer: never touches GL. Just records lifecycle.
internal sealed class FakeRenderer : IChunkRenderer
{
    public bool Disposed { get; private set; }
    public int DrawCount { get; private set; }
    public float[] Mesh { get; }

    public FakeRenderer(float[] mesh) { this.Mesh = mesh; }
    public void Draw() => this.DrawCount++;
    public void Dispose() => this.Disposed = true;
}

// Minimal mesher returning a fixed-length non-empty mesh.
internal sealed class FakeMesher : IChunkMesher
{
    public float[] Build(VoxelChunk chunk, BlockRegistry registry, Func<int, int, int, bool>? neighborOpaqueOutside = null)
        => new float[6]; // one vertex worth
}

public class ChunkStreamerTests
{
    private static (ChunkStreamer streamer, World.World world, List<FakeRenderer> created) CreateStreamer(Configuration cfg)
    {
        var registry = new BlockRegistry();
        var store = new InMemoryChunkModificationStore();
        var world = new World.World(registry, store);
        var mesher = new FakeMesher();
        var executor = new SynchronousJobExecutor();
        var created = new List<FakeRenderer>();
        Func<float[], IChunkRenderer> factory = m =>
        {
            var r = new FakeRenderer(m);
            created.Add(r);
            return r;
        };
        Func<Vector3i, VoxelChunk> generate = _ => new VoxelChunk();
        var streamer = new ChunkStreamer(cfg, world, generate, mesher, registry, executor, factory);
        return (streamer, world, created);
    }

    [Fact]
    public void Tick_FirstCall_LoadsAllChunksInLoadBox()
    {
        var cfg = new Configuration
        {
            RenderDistanceHorizontal = 1,
            RenderDistanceVertical = 0,
            MaxGenerateJobsInFlight = 100,
            MaxMeshUploadsPerFrame = 100,
        };
        var (streamer, world, created) = CreateStreamer(cfg);

        streamer.Tick(new Vector3i(0, 0, 0));

        // Load box H=1, V=0 → 3 × 1 × 3 = 9 chunks
        Assert.Equal(9, created.Count);
        for (int x = -1; x <= 1; x++)
        for (int z = -1; z <= 1; z++)
        {
            var pos = new Vector3i(x, 0, z);
            Assert.NotNull(world.GetChunk(pos));
            Assert.True(streamer.IsReady(pos));
        }
    }

    [Fact]
    public void Tick_PlayerMoves_LoadsNewChunks()
    {
        var cfg = new Configuration
        {
            RenderDistanceHorizontal = 1,
            RenderDistanceVertical = 0,
            MaxGenerateJobsInFlight = 100,
            MaxMeshUploadsPerFrame = 100,
        };
        var (streamer, world, created) = CreateStreamer(cfg);

        streamer.Tick(new Vector3i(0, 0, 0));     // loads 9

        // After the second tick the 3 new x=2 chunks must be ready.
        // Cardinal-neighbor dirty-marking may also produce remesh renderers, so
        // we assert on world state rather than an exact renderer count.
        streamer.Tick(new Vector3i(1, 0, 0));

        for (int z = -1; z <= 1; z++)
        {
            var newPos = new Vector3i(2, 0, z);
            Assert.NotNull(world.GetChunk(newPos));
            Assert.True(streamer.IsReady(newPos));
        }
        // x=-1 column must be unloaded
        for (int z = -1; z <= 1; z++)
        {
            Assert.Null(world.GetChunk(new Vector3i(-1, 0, z)));
            Assert.False(streamer.IsReady(new Vector3i(-1, 0, z)));
        }
    }

    [Fact]
    public void Tick_RespectsMaxMeshUploadsPerFrame()
    {
        var cfg = new Configuration
        {
            RenderDistanceHorizontal = 1,
            RenderDistanceVertical = 0,
            MaxGenerateJobsInFlight = 100,
            MaxMeshUploadsPerFrame = 2,   // cap drains per tick
        };
        var (streamer, _, created) = CreateStreamer(cfg);

        // With sync executor every submitted job completes immediately and
        // posts into _completed. The cap throttles how many drain per Tick().
        streamer.Tick(new Vector3i(0, 0, 0));   // dispatch fills the queue; drain ≤ 2
        Assert.Equal(2, created.Count);

        streamer.Tick(new Vector3i(0, 0, 0));   // same player chunk, drains 2 more
        Assert.Equal(4, created.Count);
    }

    [Fact]
    public void Tick_ClampsYToWorldBounds()
    {
        var cfg = new Configuration
        {
            RenderDistanceHorizontal = 0,
            RenderDistanceVertical = 2,
            MaxGenerateJobsInFlight = 100,
            MaxMeshUploadsPerFrame = 100,
        };
        var (streamer, world, created) = CreateStreamer(cfg);

        // Player at y=0 (chunk Y = 0). V=2 wants Y ∈ [-2, 2], but valid Y is [0, 8).
        // So only Y ∈ {0, 1, 2} qualifies → 1 × 3 × 1 = 3 chunks.
        streamer.Tick(new Vector3i(0, 0, 0));
        Assert.Equal(3, created.Count);
        Assert.NotNull(world.GetChunk(new Vector3i(0, 0, 0)));
        Assert.NotNull(world.GetChunk(new Vector3i(0, 1, 0)));
        Assert.NotNull(world.GetChunk(new Vector3i(0, 2, 0)));
    }

    [Fact]
    public void Tick_AppliesModificationDiffOnLoad()
    {
        var cfg = new Configuration
        {
            RenderDistanceHorizontal = 0,
            RenderDistanceVertical = 0,
            MaxGenerateJobsInFlight = 100,
            MaxMeshUploadsPerFrame = 100,
        };
        var registry = new BlockRegistry();
        var store = new InMemoryChunkModificationStore();
        var world = new World.World(registry, store);
        var mesher = new FakeMesher();
        var executor = new SynchronousJobExecutor();
        Func<float[], IChunkRenderer> factory = m => new FakeRenderer(m);
        Func<Vector3i, VoxelChunk> generate = _ => new VoxelChunk();  // all air

        // Pre-record an edit before the chunk loads.
        var pos = new Vector3i(0, 0, 0);
        int localIndex = (5 * VoxelChunk.Size + 6) * VoxelChunk.Size + 7;
        store.RecordEdit(pos, localIndex, registry.Stone.Id);

        var streamer = new ChunkStreamer(cfg, world, generate, mesher, registry, executor, factory);
        streamer.Tick(pos);

        Assert.Equal(registry.Stone.Id, world.GetBlock(5, 6, 7).Id);
    }

    [Fact]
    public void Tick_PlayerMovesAway_UnloadsOldChunksAndDisposesRenderer()
    {
        var cfg = new Configuration
        {
            RenderDistanceHorizontal = 0,
            RenderDistanceVertical = 0,
            MaxGenerateJobsInFlight = 100,
            MaxMeshUploadsPerFrame = 100,
        };
        var (streamer, world, created) = CreateStreamer(cfg);

        streamer.Tick(new Vector3i(0, 0, 0));   // loads (0,0,0)
        Assert.Single(created);
        Assert.NotNull(world.GetChunk(new Vector3i(0, 0, 0)));

        streamer.Tick(new Vector3i(5, 0, 0));   // (0,0,0) now out of range; (5,0,0) loaded

        Assert.True(created[0].Disposed);
        Assert.Null(world.GetChunk(new Vector3i(0, 0, 0)));
        Assert.False(streamer.IsReady(new Vector3i(0, 0, 0)));
    }

    [Fact]
    public void Tick_UnloadKeepsModificationStoreDiff()
    {
        var cfg = new Configuration
        {
            RenderDistanceHorizontal = 0,
            RenderDistanceVertical = 0,
            MaxGenerateJobsInFlight = 100,
            MaxMeshUploadsPerFrame = 100,
        };
        var registry = new BlockRegistry();
        var store = new InMemoryChunkModificationStore();
        var world = new World.World(registry, store);
        var mesher = new FakeMesher();
        var executor = new SynchronousJobExecutor();
        Func<float[], IChunkRenderer> factory = m => new FakeRenderer(m);
        Func<Vector3i, VoxelChunk> generate = _ => new VoxelChunk();
        var streamer = new ChunkStreamer(cfg, world, generate, mesher, registry, executor, factory);

        var pos = new Vector3i(0, 0, 0);
        streamer.Tick(pos);
        store.RecordEdit(pos, 0, registry.Stone.Id);

        streamer.Tick(new Vector3i(99, 0, 0));  // unloads (0,0,0)
        Assert.True(store.HasDiff(pos));        // diff survives unload
    }

    [Fact]
    public void SpawnReady_FlipsTrueOnceSpawnAreaLoaded()
    {
        var cfg = new Configuration
        {
            RenderDistanceHorizontal = 1,
            RenderDistanceVertical = 0,
            SpawnReadyRadiusHorizontal = 1,
            MaxGenerateJobsInFlight = 100,
            MaxMeshUploadsPerFrame = 1,         // throttle to expose progression
        };
        var (streamer, _, _) = CreateStreamer(cfg);

        Assert.False(streamer.SpawnReady);
        // Tick once per chunk needed (3×3×1 = 9 chunks at this Y). Spawn area
        // restricted by Y bounds (only Y=0 valid here) → 9 ticks.
        for (int i = 0; i < 9; i++) streamer.Tick(new Vector3i(0, 0, 0));
        Assert.True(streamer.SpawnReady);
    }

    [Fact]
    public void MarkDirty_RemeshesChunkOnNextTick()
    {
        var cfg = new Configuration
        {
            RenderDistanceHorizontal = 0,
            RenderDistanceVertical = 0,
            MaxGenerateJobsInFlight = 100,
            MaxMeshUploadsPerFrame = 100,
        };
        var (streamer, _, created) = CreateStreamer(cfg);

        streamer.Tick(new Vector3i(0, 0, 0));
        Assert.Single(created);
        var initialRenderer = created[0];

        streamer.MarkDirty(new Vector3i(0, 0, 0));
        streamer.Tick(new Vector3i(0, 0, 0));   // same chunk, but a remesh is queued

        // Two renderers exist over the lifetime — old disposed, new live.
        Assert.Equal(2, created.Count);
        Assert.True(initialRenderer.Disposed);
        Assert.False(created[1].Disposed);
    }

    [Fact]
    public void Tick_LoadingChunk_MarksReadyCardinalNeighborsDirty()
    {
        var cfg = new Configuration
        {
            RenderDistanceHorizontal = 1,
            RenderDistanceVertical = 0,
            MaxGenerateJobsInFlight = 100,
            MaxMeshUploadsPerFrame = 100,
        };
        var (streamer, _, created) = CreateStreamer(cfg);

        streamer.Tick(new Vector3i(0, 0, 0));   // load initial 3×3
        int firstWave = created.Count;           // 9 chunks

        // Move so we load a new x=2 column. The new chunks become ready and
        // mark their cardinal neighbors (x=1 column) dirty during Drain.
        streamer.Tick(new Vector3i(1, 0, 0));    // dispatch + drain new loads → dirty marks set
        streamer.Tick(new Vector3i(1, 0, 0));    // dispatch the queued remeshes → drain them

        // Should have: 3 new loads + at least 3 remeshes of the x=1 column.
        Assert.True(created.Count > firstWave + 3,
            $"Expected remeshes beyond the 3 new loads; got {created.Count - firstWave}");
    }

    [Fact]
    public void MarkDirty_OnUntrackedChunk_IsNoOp()
    {
        var cfg = new Configuration { RenderDistanceHorizontal = 0, RenderDistanceVertical = 0 };
        var (streamer, _, created) = CreateStreamer(cfg);

        streamer.MarkDirty(new Vector3i(99, 0, 99));
        streamer.Tick(new Vector3i(0, 0, 0));

        // Only the chunk in the load box was created; no spurious remesh.
        Assert.Single(created);
    }
}