using System;
using System.Collections.Generic;
using System.Numerics;
using AcDream.Core.Physics;
using Xunit;

namespace AcDream.Core.Tests.Physics;

public class PhysicsEngineTests
{
    private static float[] LinearHeightTable()
    {
        var table = new float[256];
        for (int i = 0; i < 256; i++) table[i] = i * 1.0f;
        return table;
    }

    private static byte[] FlatHeightmap(byte value = 50)
    {
        var heights = new byte[81];
        Array.Fill(heights, value);
        return heights;
    }

    private PhysicsEngine MakeFlatEngine(float terrainZ = 50f)
    {
        var engine = new PhysicsEngine();
        var terrain = new TerrainSurface(FlatHeightmap((byte)terrainZ), LinearHeightTable());
        engine.AddLandblock(0xA9B4FFFFu, terrain, Array.Empty<CellSurface>(), Array.Empty<PortalPlane>(),
            worldOffsetX: 0f, worldOffsetY: 0f);
        return engine;
    }

    [Fact]
    public void ResolveWithTransition_OutdoorCellBoundary_UpdatesLowCellId()
    {
        var engine = MakeFlatEngine(terrainZ: 50f);

        var result = engine.ResolveWithTransition(
            currentPos: new Vector3(23f, 10f, 50f),
            targetPos:  new Vector3(25f, 10f, 50f),
            cellId: 0x0001u,
            sphereRadius: 0.5f,
            sphereHeight: 1.2f,
            stepUpHeight: 0.4f,
            stepDownHeight: 0.4f,
            isOnGround: true);

        Assert.True(result.IsOnGround);
        Assert.InRange(result.Position.X, 24.9f, 25.1f);
        // Phase D fix: ResolveOutdoorCellId now always applies the matched
        // landblock's high-16 prefix — 0xA9B4 prefix from the registered
        // landblock (0xA9B4FFFF) is now included in the returned CellId.
        Assert.Equal(0xA9B40009u, result.CellId);
    }

    [Fact]
    public void ResolveWithTransition_EdgeSlideFlag_AllowsNormalFlatMovement()
    {
        var engine = MakeFlatEngine(terrainZ: 50f);

        var result = engine.ResolveWithTransition(
            currentPos: new Vector3(96f, 96f, 50f),
            targetPos:  new Vector3(98f, 96f, 50f),
            cellId: 0x0025u,
            sphereRadius: 0.5f,
            sphereHeight: 1.2f,
            stepUpHeight: 0.4f,
            stepDownHeight: 0.4f,
            isOnGround: true,
            moverFlags: ObjectInfoState.EdgeSlide);

        Assert.True(result.IsOnGround);
        Assert.InRange(result.Position.X, 97.9f, 98.1f);
        // Phase D fix: ResolveOutdoorCellId now always applies the matched
        // landblock's high-16 prefix — 0xA9B4 prefix from the registered
        // landblock (0xA9B4FFFF) is now included in the returned CellId.
        Assert.Equal(0xA9B40025u, result.CellId);
    }

    [Fact]
    public void ResolveWithTransition_EdgeSlideStopsAtLoadedTerrainBoundary()
    {
        var engine = MakeFlatEngine(terrainZ: 50f);
        var body = new PhysicsBody
        {
            Position = new Vector3(191.25f, 96f, 50f),
            TransientState = TransientStateFlags.Contact | TransientStateFlags.OnWalkable,
            ContactPlaneValid = true,
            ContactPlane = new Plane(Vector3.UnitZ, -50f),
            ContactPlaneCellId = 0x003Du,
        };

        var result = engine.ResolveWithTransition(
            currentPos: new Vector3(191.25f, 96f, 50f),
            targetPos:  new Vector3(193f, 96f, 50f),
            cellId: 0x003Du,
            sphereRadius: 0.5f,
            sphereHeight: 1.2f,
            stepUpHeight: 0.4f,
            stepDownHeight: 0.4f,
            isOnGround: true,
            body: body,
            moverFlags: ObjectInfoState.EdgeSlide);

        Assert.True(result.IsOnGround);
        Assert.InRange(result.Position.X, 190.75f, 192.0001f);
        Assert.Equal(50f, result.Position.Z, precision: 2);
    }

    [Fact]
    public void ResolveWithTransition_EdgeSlideAtLoadedTerrainBoundary_PreservesTangentMotion()
    {
        var engine = MakeFlatEngine(terrainZ: 50f);
        var body = new PhysicsBody
        {
            Position = new Vector3(191f, 96f, 50f),
            TransientState = TransientStateFlags.Contact | TransientStateFlags.OnWalkable,
            ContactPlaneValid = true,
            ContactPlane = new Plane(Vector3.UnitZ, -50f),
            ContactPlaneCellId = 0x003Du,
        };

        var settled = engine.ResolveWithTransition(
            currentPos: new Vector3(191f, 96f, 50f),
            targetPos:  new Vector3(191.25f, 96f, 50f),
            cellId: 0x003Du,
            sphereRadius: 0.5f,
            sphereHeight: 1.2f,
            stepUpHeight: 0.4f,
            stepDownHeight: 0.4f,
            isOnGround: true,
            body: body,
            moverFlags: ObjectInfoState.EdgeSlide);

        Assert.True(body.WalkablePolygonValid);
        Assert.NotNull(body.WalkableVertices);

        var result = engine.ResolveWithTransition(
            currentPos: settled.Position,
            targetPos:  new Vector3(193f, 98f, 50f),
            cellId: 0x003Du,
            sphereRadius: 0.5f,
            sphereHeight: 1.2f,
            stepUpHeight: 0.4f,
            stepDownHeight: 0.4f,
            isOnGround: true,
            body: body,
            moverFlags: ObjectInfoState.EdgeSlide);

        Assert.True(result.IsOnGround);
        Assert.InRange(result.Position.X, 190.75f, 192.0001f);
        Assert.True(result.Position.Y > 96.2f);
        Assert.Equal(50f, result.Position.Z, precision: 2);
    }

    [Fact]
    public void ResolveWithTransition_LandblockBoundary_UpdatesFullOutdoorCellId()
    {
        var engine = new PhysicsEngine();

        var terrainA = new TerrainSurface(FlatHeightmap(50), LinearHeightTable());
        engine.AddLandblock(0xA9B4FFFFu, terrainA, Array.Empty<CellSurface>(),
            Array.Empty<PortalPlane>(), worldOffsetX: 0f, worldOffsetY: 0f);

        var terrainB = new TerrainSurface(FlatHeightmap(50), LinearHeightTable());
        engine.AddLandblock(0xAAB4FFFFu, terrainB, Array.Empty<CellSurface>(),
            Array.Empty<PortalPlane>(), worldOffsetX: 192f, worldOffsetY: 0f);

        var result = engine.ResolveWithTransition(
            currentPos: new Vector3(191f, 10f, 50f),
            targetPos:  new Vector3(193f, 10f, 50f),
            cellId: 0xA9B40039u,
            sphereRadius: 0.5f,
            sphereHeight: 1.2f,
            stepUpHeight: 0.4f,
            stepDownHeight: 0.4f,
            isOnGround: true);

        Assert.True(result.IsOnGround);
        Assert.InRange(result.Position.X, 192.9f, 193.1f);
        Assert.Equal(0xAAB40001u, result.CellId);
    }

    /// <summary>
    /// #42 lock — when the moving entity's own ShadowEntry is registered
    /// in <see cref="ShadowObjectRegistry"/> at the body's exact position
    /// (the production pattern from <c>GameWindow.cs:2545</c> spawn → register
    /// + <c>UpdatePosition</c> live tracking), the airborne sweep MUST skip
    /// it. Without the gate, <c>FindObjCollisions</c> sees the cylinder as
    /// a foreign collidable and slides the sphere ~1m horizontally on the
    /// first non-zero-motion frame — the bug observed by the [SWEEP-OBJ]
    /// trace and reported as the post-jump XY drift in #42.
    /// <para>
    /// Mirrors retail's self-skip at <c>CObjCell::find_obj_collisions</c>
    /// (named-retail <c>acclient_2013_pseudo_c.txt:308931</c>):
    /// <c>physobj != arg2->object_info.object</c>.
    /// </para>
    /// </summary>
    [Fact]
    public void ResolveWithTransition_SelfShadowEntry_NotPushedWhenIdMatches()
    {
        var freshCache = new PhysicsDataCache();
        var engine = new PhysicsEngine { DataCache = freshCache };
        engine.AddLandblock(
            0xA9B4FFFFu,
            new TerrainSurface(FlatHeightmap(50), LinearHeightTable()),
            Array.Empty<CellSurface>(),
            Array.Empty<PortalPlane>(),
            worldOffsetX: 0f,
            worldOffsetY: 0f);
        // FindObjCollisions early-returns when DataCache is null. An empty
        // cache is enough for cylinder objects; only BSP objects look up
        // entries inside.
        // #145 D: register terrain for 0xA9B4 at (0,0,0) so TryGetTerrainOrigin
        // succeeds for the outdoor seed cell (0xA9B40039). In production the
        // streaming-center landblock is always resident before outdoor resolves run;
        // we replicate that invariant here by registering a flat dummy terrain.
        freshCache.CellGraph.RegisterTerrain(0xA9B4FFFFu, new TerrainSurface(FlatHeightmap(50), LinearHeightTable()), Vector3.Zero);

        const uint movingEntityId = 0xDEADBEEFu;
        var bodyPos   = new Vector3(96f, 96f, 50f);
        var targetPos = bodyPos + new Vector3(0f, 0f, 0.022f);   // stationary +Z

        // Register the moving entity's own ShadowEntry — humanoid Cylinder
        // sized to match the live-spawn registration in production
        // (GameWindow.cs:2545). The gfxObj id 0x02000001 is the standard
        // human setup; radius/height match the [SWEEP-OBJ] trace observed
        // during run #2 of the #42 investigation.
        engine.ShadowObjects.Register(
            entityId:      movingEntityId,
            gfxObjId:      0x02000001u,
            worldPos:      bodyPos,
            rotation:      Quaternion.Identity,
            radius:        0.679f,
            worldOffsetX:  0f, worldOffsetY: 0f,
            landblockId:   0xA9B4FFFFu,
            collisionType: ShadowCollisionType.Cylinder,
            cylHeight:     1.835f);

        // Without the gate (movingEntityId == 0): the sweep must be
        // INTERFERED WITH by the self-entry. This proves the registry
        // actually causes a collision, so the following filtered case is not
        // a vacuous pass.
        //
        // Observable updated for the 2026-07-05 CCylSphere family port: the
        // old hand-rolled response radial-pushed the sphere ~1 m sideways
        // (the original #42 symptom this test asserted). Retail's dispatcher
        // (0x0053b440) resolves this geometry — airborne, dead-center on the
        // cylinder axis, moving up — through land_on_cylinder → the Collide
        // re-test, whose interp gate hard-stops (COLLIDED); ValidateTransition
        // then reverts to a stay-put (no sideways teleport, Ok=true). The
        // response-model-independent interference signal is the DENIED +Z
        // movement: the sweep must NOT reach the +0.022 target.
        var unfiltered = engine.ResolveWithTransition(
            currentPos: bodyPos, targetPos: targetPos,
            cellId: 0xA9B40039u,
            sphereRadius: 0.48f, sphereHeight: 1.2f,
            stepUpHeight: 0.4f, stepDownHeight: 0.4f,
            isOnGround: false,
            movingEntityId: 0u);

        Assert.True(unfiltered.Position.Z < targetPos.Z - 0.01f,
            $"Without movingEntityId, the sweep must collide with the mover's own " +
            $"ShadowEntry and deny the +Z movement (retail: land_on_cylinder → " +
            $"Collide re-test → COLLIDED → stay-put). Got Z={unfiltered.Position.Z:F4}, " +
            $"target Z={targetPos.Z:F4}");

        // With the gate: the sweep must leave XY unchanged.
        var filtered = engine.ResolveWithTransition(
            currentPos: bodyPos, targetPos: targetPos,
            cellId: 0xA9B40039u,
            sphereRadius: 0.48f, sphereHeight: 1.2f,
            stepUpHeight: 0.4f, stepDownHeight: 0.4f,
            isOnGround: false,
            movingEntityId: movingEntityId);

        float filteredXY = MathF.Sqrt(
            (filtered.Position.X - targetPos.X) * (filtered.Position.X - targetPos.X) +
            (filtered.Position.Y - targetPos.Y) * (filtered.Position.Y - targetPos.Y));
        Assert.InRange(filteredXY, 0f, 0.001f);
    }
}