// Tests for EnvCellRenderer (Phase A8, 2026-05-28).
// These cover the pure data-handling portions of EnvCellRenderer.
// The GL-dependent Render() and RenderModernMDIInternal() paths require a
// GL context and are visual-verified at the render frame (Task 10).

using System.Collections.Generic;
using System.Numerics;
using System.Runtime.InteropServices;
using AcDream.App.Rendering.Wb;
using Xunit;

namespace AcDream.App.Tests.Rendering.Wb;

public class EnvCellRendererTests
{
    // -----------------------------------------------------------------------
    // GetEnvCellGeomId — verbatim port of WB EnvCellRenderManager.cs:94-103
    // -----------------------------------------------------------------------

    [Fact]
    public void GetEnvCellGeomId_DedupBitSet()
    {
        var id = EnvCellRenderer.GetEnvCellGeomId(0x42, 7, new List<ushort> { 1, 2, 3 });
        // Bit 33 (0x2_0000_0000) must be set — distinguishes dedup geom from per-cell ids.
        Assert.NotEqual(0UL, id & 0x2_0000_0000UL);
    }

    [Fact]
    public void GetEnvCellGeomId_Deterministic()
    {
        var s = new List<ushort> { 1, 2, 3 };
        var a = EnvCellRenderer.GetEnvCellGeomId(0x42, 7, s);
        var b = EnvCellRenderer.GetEnvCellGeomId(0x42, 7, s);
        Assert.Equal(a, b);
    }

    [Fact]
    public void GetEnvCellGeomId_DiffersByEnvironmentId()
    {
        var a = EnvCellRenderer.GetEnvCellGeomId(0x42, 7, new List<ushort> { 1 });
        var b = EnvCellRenderer.GetEnvCellGeomId(0x43, 7, new List<ushort> { 1 });
        Assert.NotEqual(a, b);
    }

    [Fact]
    public void GetEnvCellGeomId_DiffersByCellStructure()
    {
        var a = EnvCellRenderer.GetEnvCellGeomId(0x42, 7, new List<ushort> { 1 });
        var b = EnvCellRenderer.GetEnvCellGeomId(0x42, 8, new List<ushort> { 1 });
        Assert.NotEqual(a, b);
    }

    [Fact]
    public void GetEnvCellGeomId_DiffersBySurfaces()
    {
        var a = EnvCellRenderer.GetEnvCellGeomId(0x42, 7, new List<ushort> { 1 });
        var b = EnvCellRenderer.GetEnvCellGeomId(0x42, 7, new List<ushort> { 2 });
        Assert.NotEqual(a, b);
    }

    // -----------------------------------------------------------------------
    // Constructor — pure data, no GL
    // -----------------------------------------------------------------------

    [Fact]
    public void NewRenderer_NeedsPrepareIsTrue()
    {
        // GL and meshManager are null — only valid for pure-data tests (no
        // Initialize() is called, so no GL calls are made).
        var r = new EnvCellRenderer(gl: null!, meshManager: null!, frustum: new WbFrustum());
        Assert.True(r.NeedsPrepare);
    }

    [Fact]
    public void NewRenderer_NotDisposed()
    {
        var r = new EnvCellRenderer(gl: null!, meshManager: null!, frustum: new WbFrustum());
        Assert.False(r.IsDisposed);
    }

    // -----------------------------------------------------------------------
    // RemoveLandblock — pure data path
    // -----------------------------------------------------------------------

    [Fact]
    public void RemoveLandblock_NonExistent_DoesNotThrow()
    {
        var r = new EnvCellRenderer(gl: null!, meshManager: null!, frustum: new WbFrustum());
        // Should silently no-op.
        r.RemoveLandblock(0xA9B40000u);
        Assert.True(r.NeedsPrepare);
    }

    // -----------------------------------------------------------------------
    // GetEnvCellGeomId — additional edge cases
    // -----------------------------------------------------------------------

    [Fact]
    public void GetEnvCellGeomId_EmptySurfaces_Deterministic()
    {
        var a = EnvCellRenderer.GetEnvCellGeomId(1, 0, new List<ushort>());
        var b = EnvCellRenderer.GetEnvCellGeomId(1, 0, new List<ushort>());
        Assert.Equal(a, b);
        Assert.NotEqual(0UL, a & 0x2_0000_0000UL);
    }

    [Fact]
    public void GetEnvCellGeomId_SurfaceOrderMatters()
    {
        var a = EnvCellRenderer.GetEnvCellGeomId(1, 1, new List<ushort> { 10, 20 });
        var b = EnvCellRenderer.GetEnvCellGeomId(1, 1, new List<ushort> { 20, 10 });
        // The hash is order-sensitive (matches WB's foreach loop), so
        // swapped order should produce a different id.
        Assert.NotEqual(a, b);
    }

    // (Render() requires a GL context — visual-verified in Task 10.)

    [Fact]
    public void GpuInstanceUpload_UsesMeshModernMat4Stride()
    {
        // mesh_modern.vert declares SSBO InstanceData as exactly one mat4,
        // so the GPU array stride is 64 bytes. EnvCellRenderer's CPU
        // InstanceData also carries CellId/Flags for culling/filtering and
        // is 80 bytes; uploading that struct corrupts every instance after 0.
        Assert.Equal(64, Marshal.SizeOf<Matrix4x4>());
        Assert.Equal(80, Marshal.SizeOf<InstanceData>());

        var field = typeof(EnvCellRenderer).GetField("_gpuInstanceTransforms",
            System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
        Assert.NotNull(field);
        Assert.Equal(typeof(Matrix4x4[]), field!.FieldType);
    }

    // -----------------------------------------------------------------------
    // Pool-aliasing regression tests (2026-05-28 audit findings).
    //
    // Two interconnected bugs caused the post-Wave-5 visual chaos:
    //   1. GetPooledList didn't clear reused lists, causing AddRange to grow
    //      pool entries unbounded across frames.
    //   2. Render's pool cursor reset used `BatchedByCell.Count` (cell count,
    //      a small int with no relation to the pool) instead of WB's
    //      `PostPreparePoolIndex` (the pool high-water mark after Prepare),
    //      pointing Render's GetPooledList back into snapshot-owned lists.
    //
    // These tests use reflection to verify the fixes without widening
    // EnvCellRenderer's public API. If either fix regresses, the
    // corresponding test fails fast.
    // -----------------------------------------------------------------------

    [Fact]
    public void Snapshot_PostPreparePoolIndex_IsInitSettable()
    {
        // Compile-time guarantee: the field exists and is init-only.
        // If a future refactor renames or removes it, this test won't compile.
        var s = new EnvCellVisibilitySnapshot { PostPreparePoolIndex = 42 };
        Assert.Equal(42, s.PostPreparePoolIndex);
    }

    [Fact]
    public void Snapshot_PostPreparePoolIndex_DefaultsToZero()
    {
        var s = new EnvCellVisibilitySnapshot();
        Assert.Equal(0, s.PostPreparePoolIndex);
    }

    [Fact]
    public void GetPooledList_ReusedList_IsClearedBeforeReturn()
    {
        // The bug: WB's GetPooledList clears the list before returning so
        // the merge phase pattern `gfxDict[k] = list; list.AddRange(...)`
        // populates fresh data. The original port omitted Clear() — each
        // frame's lists grew unbounded with stale data layered on top.
        //
        // Reflection-based test that drives the private GetPooledList +
        // _poolIndex/_listPool fields. If a future refactor removes the
        // Clear() call, this test fails.
        var r = new EnvCellRenderer(gl: null!, meshManager: null!, frustum: new WbFrustum());

        var type = typeof(EnvCellRenderer);
        var getPooledListMethod = type.GetMethod("GetPooledList",
            System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
        Assert.NotNull(getPooledListMethod);
        var poolIndexField = type.GetField("_poolIndex",
            System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
        Assert.NotNull(poolIndexField);

        // First call — creates _listPool[0], _poolIndex 0 → 1.
        var first = (List<InstanceData>)getPooledListMethod!.Invoke(r, null)!;
        first.Add(new InstanceData());
        first.Add(new InstanceData());
        Assert.Equal(2, first.Count);

        // Reset cursor to 0 — simulates the start of the next prepare cycle.
        poolIndexField!.SetValue(r, 0);

        // Second call — returns _listPool[0] (same as first). With the fix
        // it should be cleared. Without the fix the list still has 2 items.
        var second = (List<InstanceData>)getPooledListMethod.Invoke(r, null)!;
        Assert.Same(first, second);            // reuses the same instance
        Assert.Empty(second);                  // and the data is gone
    }

    [Fact]
    public void GetPooledList_FreshList_IsAlwaysEmpty()
    {
        // Sanity check for the fresh-list branch. _poolIndex past _listPool.Count
        // should produce a brand-new empty list and grow the pool.
        var r = new EnvCellRenderer(gl: null!, meshManager: null!, frustum: new WbFrustum());

        var type = typeof(EnvCellRenderer);
        var getPooledListMethod = type.GetMethod("GetPooledList",
            System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);

        var a = (List<InstanceData>)getPooledListMethod!.Invoke(r, null)!;
        var b = (List<InstanceData>)getPooledListMethod.Invoke(r, null)!;

        Assert.NotSame(a, b);
        Assert.Empty(a);
        Assert.Empty(b);
    }
}