using System.Collections.Generic;
using System.Numerics;
using AcDream.App.Rendering;
using AcDream.App.Rendering.Wb;
using AcDream.Core.Meshing;
using AcDream.Core.World;
using Xunit;

namespace AcDream.Core.Tests.Rendering.Wb;

/// <summary>
/// Tests for <see cref="WbDrawDispatcher.WalkEntities"/> — the pure-CPU
/// visibility filter extracted in A.5 T17. These tests exercise the two
/// key perf changes from Phase A.5 spec §4.6:
///
/// <list type="bullet">
///   <item>Change #1 (T17): invisible LB + animated set → iterate
///         <c>animatedEntityIds</c> directly, not the full entity list.</item>
///   <item>Change #2 (T18): per-entity AABB cull reads the cached AABB
///         (<see cref="WorldEntity.AabbMin"/>/<c>AabbMax</c>) rather than
///         recomputing Position±5 per frame.</item>
/// </list>
/// </summary>
public sealed class WbDrawDispatcherBucketingTests
{
    // ── helpers ──────────────────────────────────────────────────────────────

    private static WorldEntity MakeEntity(uint id, Vector3 position)
        => new WorldEntity
        {
            Id = id,
            SourceGfxObjOrSetupId = 0,
            Position = position,
            Rotation = Quaternion.Identity,
            MeshRefs = System.Array.Empty<MeshRef>(),
        };

    private static WorldEntity MakeEntityWithMesh(uint id, Vector3 position)
        => new WorldEntity
        {
            Id = id,
            SourceGfxObjOrSetupId = 0,
            Position = position,
            Rotation = Quaternion.Identity,
            // Single dummy MeshRef so it passes the MeshRefs.Count == 0 guard.
            MeshRefs = new[] { new MeshRef { GfxObjId = 0x01000001u } },
        };

    private static Dictionary<uint, WorldEntity> BuildById(IEnumerable<WorldEntity> entities)
    {
        var d = new Dictionary<uint, WorldEntity>();
        foreach (var e in entities) d[e.Id] = e;
        return d;
    }

    /// <summary>
    /// A frustum positioned at (1e6+1, 1e6+1, 1e6+1) looking toward (1e6, 1e6, 1e6)
    /// with a very narrow near/far. Any AABB near the origin (0..20000) is
    /// far behind the near plane and fails all six planes.
    /// </summary>
    private static FrustumPlanes MakeFarAwayFrustum()
    {
        var view = Matrix4x4.CreateLookAt(
            new Vector3(1e6f + 1f, 1e6f + 1f, 1e6f + 1f),
            new Vector3(1e6f, 1e6f, 1e6f),
            Vector3.UnitZ);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(
            MathF.PI / 4f, 1f, 0.1f, 1f);
        return FrustumPlanes.FromViewProjection(view * proj);
    }

    // ── T17 Change #1 tests ───────────────────────────────────────────────

    [Fact]
    public void WalkEntities_InvisibleLb_NoAnimated_SkipsEntireBlock()
    {
        // When LB is invisible AND animatedEntityIds is empty/null,
        // WalkEntities should not walk any entities at all.
        var entities = new List<WorldEntity>();
        for (int i = 0; i < 500; i++)
            entities.Add(MakeEntityWithMesh((uint)i, new Vector3(i, 0, 0)));

        var byId = BuildById(entities);
        var entries = new[]
        {
            new WbDrawDispatcher.LandblockEntry(
                0xAAAA_FFFFu,
                new Vector3(10000, 10000, 10000),
                new Vector3(20000, 20000, 20000),
                entities,
                byId),
        };

        var result = WbDrawDispatcher.WalkEntities(
            entries,
            frustum: MakeFarAwayFrustum(),
            neverCullLandblockId: null,
            visibleCellIds: null,
            animatedEntityIds: null);

        Assert.Equal(0, result.EntitiesWalked);
        Assert.Empty(result.ToDraw);
    }

    [Fact]
    public void WalkEntities_InvisibleLb_AnimatedSet_WalksOnlyAnimatedEntities()
    {
        // 1000 entities in an LB whose AABB is far outside the frustum.
        // Only entity Id=42 is in animatedEntityIds.
        // Pre-T17 behavior: walk all 1000 entities just to find #42.
        // Post-T17: walk only the 1 animated entity (EntitiesWalked == 1).
        const int Total = 1000;
        var entities = new List<WorldEntity>(Total);
        for (int i = 0; i < Total; i++)
            entities.Add(MakeEntityWithMesh((uint)i, new Vector3(i, 0, 0)));

        var byId = BuildById(entities);
        var animatedSet = new HashSet<uint> { 42 };

        var entries = new[]
        {
            new WbDrawDispatcher.LandblockEntry(
                0xAAAA_FFFFu,
                new Vector3(10000, 10000, 10000),
                new Vector3(20000, 20000, 20000),
                entities,
                byId),
        };

        var result = WbDrawDispatcher.WalkEntities(
            entries,
            frustum: MakeFarAwayFrustum(),
            neverCullLandblockId: null,
            visibleCellIds: null,
            animatedEntityIds: animatedSet);

        // Only the 1 animated entity should be walked — not 1000.
        Assert.Equal(1, result.EntitiesWalked);
        Assert.Single(result.ToDraw);
        Assert.Equal(42u, result.ToDraw[0].Entity.Id);
    }

    [Fact]
    public void WalkEntities_InvisibleLb_AnimatedIdAbsent_ZeroWalked()
    {
        // Animated entity ids 200 and 300 are NOT in this LB (which only
        // has ids 0..99). Should produce zero walks.
        var entities = new List<WorldEntity>();
        for (int i = 0; i < 100; i++)
            entities.Add(MakeEntityWithMesh((uint)i, Vector3.Zero));

        var byId = BuildById(entities);
        var animatedSet = new HashSet<uint> { 200, 300 }; // not in this LB

        var entries = new[]
        {
            new WbDrawDispatcher.LandblockEntry(
                0xBBBB_FFFFu,
                new Vector3(10000, 10000, 10000),
                new Vector3(20000, 20000, 20000),
                entities,
                byId),
        };

        var result = WbDrawDispatcher.WalkEntities(
            entries,
            frustum: MakeFarAwayFrustum(),
            neverCullLandblockId: null,
            visibleCellIds: null,
            animatedEntityIds: animatedSet);

        Assert.Equal(0, result.EntitiesWalked);
        Assert.Empty(result.ToDraw);
    }

    [Fact]
    public void WalkEntities_NeverCullLb_WalksAllEntitiesRegardlessOfFrustum()
    {
        // neverCullLandblockId bypasses the LB AABB check entirely.
        // All entities with at least one MeshRef should be walked.
        var entities = new List<WorldEntity>
        {
            MakeEntityWithMesh(1, Vector3.Zero),
            MakeEntityWithMesh(2, Vector3.Zero),
            MakeEntityWithMesh(3, Vector3.Zero),
        };

        var byId = BuildById(entities);
        const uint lbId = 0xCCCC_FFFFu;

        var entries = new[]
        {
            new WbDrawDispatcher.LandblockEntry(
                lbId,
                new Vector3(10000, 10000, 10000), // AABB would fail frustum
                new Vector3(20000, 20000, 20000),
                entities,
                byId),
        };

        var result = WbDrawDispatcher.WalkEntities(
            entries,
            frustum: MakeFarAwayFrustum(),
            neverCullLandblockId: lbId, // exempt from LB cull
            visibleCellIds: null,
            animatedEntityIds: null);

        Assert.Equal(3, result.EntitiesWalked);
    }

    [Fact]
    public void WalkEntities_NullFrustum_WalksEntitiesWithMeshRefs()
    {
        // Null frustum means no culling — all entities with MeshRefs pass.
        // Entities without MeshRefs are still filtered out.
        var entities = new List<WorldEntity>
        {
            MakeEntityWithMesh(1, Vector3.Zero),
            MakeEntity(2, Vector3.Zero),          // no MeshRefs — must be skipped
            MakeEntityWithMesh(3, Vector3.Zero),
        };

        var byId = BuildById(entities);
        var entries = new[]
        {
            new WbDrawDispatcher.LandblockEntry(
                0xDDDD_FFFFu, Vector3.Zero, Vector3.Zero,
                entities, byId),
        };

        var result = WbDrawDispatcher.WalkEntities(
            entries,
            frustum: null,
            neverCullLandblockId: null,
            visibleCellIds: null,
            animatedEntityIds: null);

        Assert.Equal(2, result.EntitiesWalked);
        Assert.Equal(2, result.ToDraw.Count);
    }

    // ── T18 Change #2 tests ───────────────────────────────────────────────

    [Fact]
    public void WalkEntities_VisibleLb_EntityFarAway_CulledViaCachedAabb()
    {
        // LB passes the LB-level cull; entity AABB is far from the frustum.
        // After RefreshAabb the entity should be culled by the per-entity check.
        var entity = MakeEntityWithMesh(1, new Vector3(50000, 50000, 50000));
        entity.RefreshAabb(); // populate cached AABB at (50000±5)

        var byId = BuildById(new[] { entity });
        var entries = new[]
        {
            // LB AABB near origin so it passes the LB cull; entity is far away.
            new WbDrawDispatcher.LandblockEntry(
                0xEEEE_FFFFu,
                new Vector3(-10, -10, -10),
                new Vector3(10, 10, 10),
                new List<WorldEntity> { entity },
                byId),
        };

        // Frustum centered at origin, range ±100.
        var view = Matrix4x4.CreateLookAt(new Vector3(-50, 0, 0), Vector3.Zero, Vector3.UnitZ);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(MathF.PI / 2f, 1f, 0.5f, 100f);
        var tightFrustum = FrustumPlanes.FromViewProjection(view * proj);

        var result = WbDrawDispatcher.WalkEntities(
            entries,
            frustum: tightFrustum,
            neverCullLandblockId: null,
            visibleCellIds: null,
            animatedEntityIds: null);

        // Entity at (50000,50000,50000) is outside the frustum — should be culled.
        Assert.Equal(0, result.EntitiesWalked);
    }

    [Fact]
    public void WalkEntities_AnimatedEntity_BypassesPerEntityAabbCull()
    {
        // Animated entities must always pass even if their AABB would be culled.
        var entity = MakeEntityWithMesh(7, new Vector3(50000, 50000, 50000));
        entity.RefreshAabb();

        var byId = BuildById(new[] { entity });
        var entries = new[]
        {
            new WbDrawDispatcher.LandblockEntry(
                0xEEEF_FFFFu,
                new Vector3(-10, -10, -10),
                new Vector3(10, 10, 10),
                new List<WorldEntity> { entity },
                byId),
        };

        var view = Matrix4x4.CreateLookAt(new Vector3(-50, 0, 0), Vector3.Zero, Vector3.UnitZ);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(MathF.PI / 2f, 1f, 0.5f, 100f);
        var tightFrustum = FrustumPlanes.FromViewProjection(view * proj);

        var animatedSet = new HashSet<uint> { 7 };

        var result = WbDrawDispatcher.WalkEntities(
            entries,
            frustum: tightFrustum,
            neverCullLandblockId: null,
            visibleCellIds: null,
            animatedEntityIds: animatedSet);

        // Animated entity bypasses per-entity cull.
        Assert.Equal(1, result.EntitiesWalked);
        Assert.Single(result.ToDraw);
        Assert.Equal(7u, result.ToDraw[0].Entity.Id);
    }

    [Fact]
    public void WalkEntities_AabbDirty_RefreshedLazilyBeforeCull()
    {
        // An entity with AabbDirty=true (initial state) should get its AABB
        // refreshed lazily by WalkEntities before the cull check.
        var entity = MakeEntityWithMesh(5, new Vector3(0, 0, 0));
        // AabbDirty starts true by default — do NOT call RefreshAabb manually.
        Assert.True(entity.AabbDirty);

        var byId = BuildById(new[] { entity });
        var entries = new[]
        {
            new WbDrawDispatcher.LandblockEntry(
                0xF0F0_FFFFu,
                new Vector3(-10, -10, -10),
                new Vector3(10, 10, 10),
                new List<WorldEntity> { entity },
                byId),
        };

        // A frustum that accepts things near origin.
        var view = Matrix4x4.CreateLookAt(new Vector3(-50, 0, 0), Vector3.Zero, Vector3.UnitZ);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(MathF.PI / 2f, 1f, 0.1f, 200f);
        var nearOriginFrustum = FrustumPlanes.FromViewProjection(view * proj);

        var result = WbDrawDispatcher.WalkEntities(
            entries,
            frustum: nearOriginFrustum,
            neverCullLandblockId: null,
            visibleCellIds: null,
            animatedEntityIds: null);

        // Entity at origin is inside the frustum after lazy RefreshAabb.
        Assert.Equal(1, result.EntitiesWalked);
        // AabbDirty should have been cleared by the lazy refresh.
        Assert.False(entity.AabbDirty);
    }
}