using System.Numerics;
using AcDream.Core.Lighting;
using Xunit;

namespace AcDream.Core.Tests.Lighting;

public sealed class LightManagerTests
{
    private static LightSource MakePoint(Vector3 pos, float range, uint ownerId = 0, bool lit = true)
        => new LightSource
        {
            Kind = LightKind.Point,
            WorldPosition = pos,
            Range = range,
            IsLit = lit,
            OwnerId = ownerId,
        };

    [Fact]
    public void Register_Unregister_TracksList()
    {
        var mgr = new LightManager();
        var a = MakePoint(Vector3.Zero, 5f);
        var b = MakePoint(new Vector3(10, 0, 0), 5f);
        mgr.Register(a);
        mgr.Register(b);
        Assert.Equal(2, mgr.RegisteredCount);

        mgr.Unregister(a);
        Assert.Equal(1, mgr.RegisteredCount);
    }

    [Fact]
    public void Register_DuplicateInstance_Idempotent()
    {
        var mgr = new LightManager();
        var light = MakePoint(Vector3.Zero, 5f);
        mgr.Register(light);
        mgr.Register(light);
        Assert.Equal(1, mgr.RegisteredCount);
    }

    [Fact]
    public void Tick_SelectsByDistance_Top8()
    {
        var mgr = new LightManager();
        // 12 lights at varying distances, all with range 100 so none filter out.
        for (int i = 0; i < 12; i++)
            mgr.Register(MakePoint(new Vector3(i, 0, 0), 100f));

        mgr.Tick(viewerWorldPos: Vector3.Zero);

        Assert.Equal(8, mgr.ActiveCount);
        // Top 8 should be the closest (i=0..7).
        foreach (var l in mgr.Active)
        {
            Assert.NotNull(l);
            Assert.True(l!.WorldPosition.X <= 7f);
        }
    }

    [Fact]
    public void Tick_SelectsByDistance_RegardlessOfViewerRange()
    {
        // Retail D3D-style: candidacy is distance-only (the nearest 8). A torch
        // lights its OWN surfaces — the shader applies the hard `d < range` cutoff
        // PER FRAGMENT (mesh_modern.frag) — so a torch the VIEWER is standing
        // outside the range of is still selected; it lights the wall it sits on.
        // Replaces the old viewer-range candidacy filter that suppressed it, which
        // left dungeon rooms (2227 registered torches) at activeLights≈1 / flat 0.2
        // ambient — the "dungeon lighting off" report (#133 A7).
        var mgr = new LightManager();
        mgr.Register(MakePoint(new Vector3(20, 0, 0), range: 5f));  // viewer outside the torch's range

        mgr.Tick(viewerWorldPos: Vector3.Zero);

        Assert.Equal(1, mgr.ActiveCount);   // selected by distance; the shader culls per-surface
    }

    [Fact]
    public void Tick_IncludesNearbyLight()
    {
        var mgr = new LightManager();
        // A nearby point light is selected (distance-only candidacy; the shader
        // applies the per-fragment range cutoff).
        mgr.Register(MakePoint(new Vector3(5, 0, 0), range: 5f));

        mgr.Tick(viewerWorldPos: Vector3.Zero);
        Assert.Equal(1, mgr.ActiveCount);
    }

    [Fact]
    public void Tick_SunSlot0_PreservedAcrossTicks()
    {
        var mgr = new LightManager();
        var sun = new LightSource { Kind = LightKind.Directional, WorldForward = -Vector3.UnitZ };
        mgr.Sun = sun;

        mgr.Register(MakePoint(Vector3.Zero, 100f));
        mgr.Tick(Vector3.Zero);

        Assert.Equal(2, mgr.ActiveCount);
        Assert.Same(sun, mgr.Active[0]);
    }

    [Fact]
    public void Tick_UnlitLight_Excluded()
    {
        var mgr = new LightManager();
        var light = MakePoint(Vector3.Zero, 100f, lit: false);
        mgr.Register(light);

        mgr.Tick(Vector3.Zero);
        Assert.Equal(0, mgr.ActiveCount);

        // Toggle lit: should now appear.
        light.IsLit = true;
        mgr.Tick(Vector3.Zero);
        Assert.Equal(1, mgr.ActiveCount);
    }

    [Fact]
    public void UnregisterByOwner_RemovesAttachedLights()
    {
        var mgr = new LightManager();
        mgr.Register(MakePoint(Vector3.Zero, 5f, ownerId: 42));
        mgr.Register(MakePoint(new Vector3(1, 0, 0), 5f, ownerId: 42));
        mgr.Register(MakePoint(new Vector3(2, 0, 0), 5f, ownerId: 99));

        mgr.UnregisterByOwner(42);
        Assert.Equal(1, mgr.RegisteredCount);
    }

    [Fact]
    public void DistSq_UpdatedEachTick()
    {
        var mgr = new LightManager();
        var light = MakePoint(new Vector3(3, 0, 4), 10f);   // dist 5
        mgr.Register(light);

        mgr.Tick(Vector3.Zero);
        Assert.Equal(25f, light.DistSq, 2);

        mgr.Tick(new Vector3(3, 0, 0));   // same x, same y, z diff 4
        Assert.Equal(16f, light.DistSq, 2);
    }
}