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, uint cellId = 0)
        => new LightSource
        {
            Kind = LightKind.Point,
            WorldPosition = pos,
            Range = range,
            IsLit = lit,
            OwnerId = ownerId,
            CellId = cellId,
        };

    private static LightSource MakeDynamic(Vector3 pos, float range, uint cellId = 0)
        => new LightSource
        {
            Kind = LightKind.Point,
            WorldPosition = pos,
            Range = range,
            IsLit = true,
            IsDynamic = true,
            CellId = cellId,
        };

    [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);
    }

    // ── Fix B: per-object selection (minimize_object_lighting) ────────────────

    [Fact]
    public void BuildPointLightSnapshot_ExcludesDirectionalAndUnlit()
    {
        var mgr = new LightManager();
        mgr.Register(MakePoint(new Vector3(1, 0, 0), 5f));               // in
        mgr.Register(MakePoint(new Vector3(2, 0, 0), 5f, lit: false));   // unlit → out
        mgr.Register(new LightSource { Kind = LightKind.Directional });  // sun → out

        mgr.BuildPointLightSnapshot(Vector3.Zero);

        Assert.Single(mgr.PointSnapshot);
        Assert.Equal(1f, mgr.PointSnapshot[0].WorldPosition.X, 3);
    }

    [Fact]
    public void BuildPointLightSnapshot_IndexStable_InBudget()
    {
        var mgr = new LightManager();
        // Registration order preserved when under MaxGlobalLights (no sort).
        mgr.Register(MakePoint(new Vector3(100, 0, 0), 5f));  // far
        mgr.Register(MakePoint(new Vector3(1, 0, 0), 5f));    // near

        mgr.BuildPointLightSnapshot(Vector3.Zero);

        Assert.Equal(2, mgr.PointSnapshot.Count);
        Assert.Equal(100f, mgr.PointSnapshot[0].WorldPosition.X, 3);  // index 0 = first registered
        Assert.Equal(1f, mgr.PointSnapshot[1].WorldPosition.X, 3);
    }

    // ── Resident collection (#176 corrected reading, 2026-07-06) ───────────────
    // Retail collects the pool from ALL RESIDENT EnvCells each frame:
    // CEnvCell::add_dynamic_lights (0x0052d410) walks the WHOLE static
    // CEnvCell::visible_cell_table — the loaded-cell registry add_visible_cell
    // (0x0052de40) fills from each activated cell + its dat visible-cell list. It
    // is NOT the per-frame portal flood; camera gaze cannot change the pool. The
    // earlier flood-scoped port (c500912b) made the under-room portal purples
    // enter/leave the pool as the camera turned — the #176 seam-floor blink.

    [Fact]
    public void PointSnapshot_ResidentCollection_CellTagDoesNotFilter()
    {
        var mgr = new LightManager();
        mgr.Register(MakePoint(new Vector3(1, 0, 0), 5f, cellId: 0xAAAA0101u));  // "visible" room
        mgr.Register(MakePoint(new Vector3(2, 0, 0), 5f, cellId: 0xAAAA0102u));  // under-room
        mgr.Register(MakePoint(new Vector3(3, 0, 0), 5f, cellId: 0u));           // cell-less (viewer fill)

        mgr.BuildPointLightSnapshot(Vector3.Zero);

        // ALL resident lights are candidates. The under-room portal light reaching
        // the corridor's pool is retail-correct — the live cdb capture
        // (tools/cdb/issue176-floor-light.cdb) showed retail applying the
        // intensity-100 purples to EVERY Hub cell; the faceted purple wedge is
        // faithful, only its gaze-coupled blinking was ours.
        Assert.Equal(3, mgr.PointSnapshot.Count);
    }

    [Fact]
    public void PointSnapshot_OverCap_DynamicsNeverEvictedByNearerStatics()
    {
        var mgr = new LightManager();
        // More statics than the cap, ALL nearer the player than every dynamic.
        for (int i = 0; i < LightManager.MaxGlobalLights + 20; i++)
            mgr.Register(MakePoint(new Vector3(i * 0.01f, 0, 0), 5f, ownerId: (uint)(i + 1)));
        // 7 dynamics farther out (retail's dynamics live in their own 7-slot pool —
        // Render::add_dynamic_light 0x0054d420 — statics can never crowd them out).
        var dyns = new LightSource[7];
        for (int i = 0; i < dyns.Length; i++)
        {
            dyns[i] = MakeDynamic(new Vector3(50f + i, 0, 0), range: 9f);
            mgr.Register(dyns[i]);
        }

        mgr.BuildPointLightSnapshot(Vector3.Zero);

        Assert.Equal(LightManager.MaxGlobalLights, mgr.PointSnapshot.Count);
        foreach (var d in dyns)
            Assert.Contains(d, mgr.PointSnapshot);
    }

    [Fact]
    public void PointSnapshot_OverCap_KeepsNearestThePlayer()
    {
        var mgr = new LightManager();
        // A big cluster far from the player (where a chase camera might sit) and
        // one torch beside the player. Retail sorts by distance to
        // Render::player_pos (insert_light 0x0054d1b0) — the near-player torch
        // must survive the cap no matter how many far lights exist.
        for (int i = 0; i < LightManager.MaxGlobalLights + 50; i++)
            mgr.Register(MakePoint(new Vector3(200f + i * 0.05f, 0, 0), 5f, ownerId: (uint)(i + 1)));
        var torch = MakePoint(new Vector3(2f, 0, 0), range: 15f, ownerId: 0xF00Du);
        mgr.Register(torch);

        mgr.BuildPointLightSnapshot(playerWorldPos: Vector3.Zero);

        Assert.Contains(torch, mgr.PointSnapshot);
    }

    [Fact]
    public void SelectForObject_EmptySnapshot_ReturnsZero()
    {
        Span<int> idx = stackalloc int[8];
        int n = LightManager.SelectForObject(System.Array.Empty<LightSource>(), Vector3.Zero, 1f, idx);
        Assert.Equal(0, n);
    }

    [Fact]
    public void SelectForObject_InRange_Selected()
    {
        var snapshot = new[] { MakePoint(new Vector3(3, 0, 0), range: 5f) };  // dist 3 < range 5
        Span<int> idx = stackalloc int[8];
        int n = LightManager.SelectForObject(snapshot, Vector3.Zero, radius: 0f, idx);
        Assert.Equal(1, n);
        Assert.Equal(0, idx[0]);
    }

    [Fact]
    public void SelectForObject_OutOfRange_Excluded()
    {
        // dist 10, range 5, radius 0 → 10 >= 5 → excluded.
        var snapshot = new[] { MakePoint(new Vector3(10, 0, 0), range: 5f) };
        Span<int> idx = stackalloc int[8];
        int n = LightManager.SelectForObject(snapshot, Vector3.Zero, radius: 0f, idx);
        Assert.Equal(0, n);
    }

    [Fact]
    public void SelectForObject_ObjectRadiusExtendsReach()
    {
        // dist 7, range 5: out of reach at radius 0, but a radius-3 object sphere
        // overlaps (7 < 5+3). The whole object catches the light — retail uses the
        // object's bounding sphere, not its centre point.
        var snapshot = new[] { MakePoint(new Vector3(7, 0, 0), range: 5f) };
        Span<int> idx = stackalloc int[8];

        Assert.Equal(0, LightManager.SelectForObject(snapshot, Vector3.Zero, radius: 0f, idx));
        Assert.Equal(1, LightManager.SelectForObject(snapshot, Vector3.Zero, radius: 3f, idx));
    }

    [Fact]
    public void SelectForObject_MoreThan8_KeepsNearest8()
    {
        // 10 candidate lights all in range; expect the 8 nearest the object centre,
        // ascending by distance, with the two farthest dropped.
        var snapshot = new LightSource[10];
        for (int i = 0; i < 10; i++)
            snapshot[i] = MakePoint(new Vector3(i + 1, 0, 0), range: 100f);  // dist i+1, all in range

        Span<int> idx = stackalloc int[8];
        int n = LightManager.SelectForObject(snapshot, Vector3.Zero, radius: 0f, idx);

        Assert.Equal(8, n);
        // Nearest-first: index 0 (dist 1) … index 7 (dist 8). The two farthest
        // (indices 8,9 / dist 9,10) are evicted.
        for (int k = 0; k < 8; k++)
            Assert.Equal(k, idx[k]);
    }

    [Fact]
    public void SelectForObject_CameraIndependent_DependsOnlyOnObjectCentre()
    {
        // Same snapshot, same object centre → identical selection regardless of
        // where any "camera" is (the method takes no camera). This is the property
        // that kills the "lights up as I approach" popping.
        var snapshot = new[]
        {
            MakePoint(new Vector3(2, 0, 0), range: 10f),
            MakePoint(new Vector3(20, 0, 0), range: 10f),  // out of reach of centre 0
        };
        Span<int> a = stackalloc int[8];
        Span<int> b = stackalloc int[8];
        int na = LightManager.SelectForObject(snapshot, Vector3.Zero, 1f, a);
        int nb = LightManager.SelectForObject(snapshot, Vector3.Zero, 1f, b);

        Assert.Equal(1, na);
        Assert.Equal(na, nb);
        Assert.Equal(a[0], b[0]);
    }

    // ── SelectForCell — retail minimize_envcell_lighting (all dynamics on every cell) ──

    [Fact]
    public void SelectForCell_AppliesAllDynamicLights_EvenOutOfReach()
    {
        // Retail enables the WHOLE dynamic subset for every cell (cdb-verified: the same
        // portal lights on every Facility Hub cell) — including ones that don't reach it,
        // since the shader's range cutoff zeroes those. Static lights still cull by reach.
        var snapshot = new[]
        {
            MakePoint(new Vector3(1, 0, 0), range: 5f),      // 0: static, reaches
            MakeDynamic(new Vector3(100, 0, 0), range: 5f),  // 1: dynamic, FAR (out of reach)
            MakeDynamic(new Vector3(2, 0, 0), range: 5f),    // 2: dynamic, near
            MakePoint(new Vector3(50, 0, 0), range: 5f),     // 3: static, far (out of reach)
        };
        Span<int> sel = stackalloc int[LightManager.MaxLightsPerObject];
        int n = LightManager.SelectForCell(snapshot, Vector3.Zero, radius: 1f, sel);

        bool d1 = false, d2 = false, s0 = false, s3 = false;
        for (int i = 0; i < n; i++)
        {
            if (sel[i] == 1) d1 = true;
            if (sel[i] == 2) d2 = true;
            if (sel[i] == 0) s0 = true;
            if (sel[i] == 3) s3 = true;
        }
        Assert.True(d1, "the FAR dynamic light must still be applied — retail enables all dynamics");
        Assert.True(d2, "the near dynamic light is applied");
        Assert.True(s0, "the near static light reaches the cell → selected");
        Assert.False(s3, "the far static light doesn't reach → not selected");
    }

    [Fact]
    public void SelectForCell_SameDynamicSet_ForCellsFarApart_NoFlap()
    {
        // The stability retail has and we lacked: two cells far apart get the SAME dynamic
        // set. A per-cell sphere-overlap cull of dynamics (the old SelectForObject path) let
        // that set differ/flip as the flood shifted → the floor lighting FLAPPED (#176).
        var snapshot = new[]
        {
            MakeDynamic(new Vector3(0, 0, 0), range: 5f),
            MakeDynamic(new Vector3(100, 0, 0), range: 5f),
        };
        Span<int> a = stackalloc int[8];
        Span<int> b = stackalloc int[8];
        int na = LightManager.SelectForCell(snapshot, new Vector3(0, 0, 0), 1f, a);
        int nb = LightManager.SelectForCell(snapshot, new Vector3(500, 0, 0), 1f, b);

        Assert.Equal(2, na);   // both dynamics on the near cell
        Assert.Equal(2, nb);   // both dynamics on the far cell too — identical, no flap
    }

    /// <summary>
    /// #176/#177 (2026-07-06, corrected same day) — the end-state pin. The pool is
    /// retail's RESIDENT collection anchored at the PLAYER: a light in range of an
    /// object near the player is selected no matter where a chase camera sits,
    /// because the camera is not an input to <c>BuildPointLightSnapshot</c> at all
    /// (the two prior camera-coupled pools — nearest-camera cap, then frame-flood
    /// scoping <c>c500912b</c> — were each a #176 flicker mechanism). Here the
    /// player stands by the torch while 400 fixtures cluster 200 m away where a
    /// camera might look: the torch must always survive the cap and light the
    /// object. See <c>docs/research/2026-07-06-a7-per-cell-lighting-pseudocode.md</c>
    /// (corrected §1.3) — <c>CEnvCell::visible_cell_table</c> is the resident-cell
    /// registry, and <c>Render::insert_light</c> (0x0054d1b0) sorts by distance to
    /// <c>Render::player_pos</c>.
    /// </summary>
    [Fact]
    public void PointSnapshot_HubScaleLightCount_ObjectSelectionIsCameraInvariant()
    {
        var mgr = new LightManager();

        // 400 fixtures clustered far away (in the direction a camera might sit),
        // all in another cell. Under either old camera-coupled pool these could
        // displace or gate the player-side torch; under the player anchor they are
        // simply the farthest candidates.
        const uint farRoom = 0xAAAA0102u;
        for (int i = 0; i < 400; i++)
            mgr.Register(MakePoint(new Vector3(200f + i * 0.05f, 0, 0), range: 5f, ownerId: (uint)(i + 1), cellId: farRoom));

        // The target torch: beside the player, in the player's room.
        const uint playerRoom = 0xAAAA0101u;
        var torch = MakePoint(new Vector3(2f, 0, 0), range: 15f, ownerId: 0xF00DF00Du, cellId: playerRoom);
        mgr.Register(torch);

        Span<int> sel = stackalloc int[LightManager.MaxLightsPerObject];

        // The player (the ONLY positional input) stands at the origin. Rebuild
        // twice to mirror consecutive frames of a rotating camera — the pool and
        // the selection must be identical (no camera input exists to vary).
        mgr.BuildPointLightSnapshot(playerWorldPos: Vector3.Zero);
        int n1 = LightManager.SelectForObject(mgr.PointSnapshot, new Vector3(0f, 0, 0), 6f, sel);
        bool torchSelected1 = SelectedContains(mgr.PointSnapshot, sel, n1, torch);

        mgr.BuildPointLightSnapshot(playerWorldPos: Vector3.Zero);
        int n2 = LightManager.SelectForObject(mgr.PointSnapshot, new Vector3(0f, 0, 0), 6f, sel);
        bool torchSelected2 = SelectedContains(mgr.PointSnapshot, sel, n2, torch);

        Assert.True(torchSelected1,
            "an in-range light beside the player was evicted from the pool — " +
            "per-cell lighting would pop (the #176/#177 mechanism)");
        Assert.True(torchSelected2, "consecutive same-player builds must select identically");
        Assert.Equal(LightManager.MaxGlobalLights, mgr.PointSnapshot.Count);  // cap applied to the far cluster

        static bool SelectedContains(
            System.Collections.Generic.IReadOnlyList<LightSource> snapshot,
            Span<int> indices, int count, LightSource target)
        {
            for (int i = 0; i < count; i++)
                if (ReferenceEquals(snapshot[indices[i]], target)) return true;
            return false;
        }
    }
}