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 Resolve_FlatTerrain_ZMatchesTerrain()
    {
        var engine = MakeFlatEngine(terrainZ: 50f);

        var result = engine.Resolve(
            new Vector3(96f, 96f, 50f), cellId: 0x0001, delta: new Vector3(1f, 0f, 0f),
            stepUpHeight: 2f);

        Assert.Equal(50f, result.Position.Z, precision: 1);
        Assert.True(result.IsOnGround);
    }

    [Fact]
    public void Resolve_WalkUpSmallSlope_Accepted()
    {
        // Heights slope from 50 to 52 across X — small enough for step height.
        var heights = new byte[81];
        for (int x = 0; x < 9; x++)
            for (int y = 0; y < 9; y++)
                heights[x * 9 + y] = (byte)(50 + x / 4);  // gentle slope

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

        var result = engine.Resolve(
            new Vector3(48f, 96f, 50f), cellId: 0x0001, delta: new Vector3(48f, 0f, 0f),
            stepUpHeight: 5f);

        Assert.True(result.IsOnGround);
        Assert.True(result.Position.Z >= 50f);  // moved uphill
    }

    [Fact]
    public void Resolve_StepUpExceedsHeight_MovementBlocked()
    {
        // Heights jump sharply: left half = 50, right half = 100.
        var heights = new byte[81];
        for (int x = 0; x < 9; x++)
            for (int y = 0; y < 9; y++)
                heights[x * 9 + y] = (byte)(x < 5 ? 50 : 100);

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

        // Try to walk from the low side to the high side.
        var result = engine.Resolve(
            new Vector3(96f, 96f, 50f), cellId: 0x0001, delta: new Vector3(48f, 0f, 0f),
            stepUpHeight: 2f);

        // Movement should be blocked — Z delta (50→100) exceeds step height (2).
        Assert.Equal(96f, result.Position.X, precision: 1);  // didn't move
        Assert.True(result.IsOnGround);
    }

    [Fact]
    public void Resolve_OutdoorThroughPortal_TransitionsToIndoor()
    {
        var engine = new PhysicsEngine();
        var terrain = new TerrainSurface(FlatHeightmap(50), LinearHeightTable());

        // A CellSurface for the indoor cell with floor at Z=50.
        var cellVerts = new Dictionary<ushort, Vector3>
        {
            [0] = new(40f, 40f, 50f),
            [1] = new(60f, 40f, 50f),
            [2] = new(60f, 60f, 50f),
            [3] = new(40f, 60f, 50f),
        };
        var cellPolys = new List<List<short>> { new() { 0, 1, 2, 3 } };
        var cell = new CellSurface(0x0100, cellVerts, cellPolys);

        // A portal plane at X=45 (vertical plane facing +X).
        // OwnerCellId = 0x0100 (the indoor cell), TargetCellId = 0xFFFF (faces outdoor).
        // From outside, walking through this portal enters OwnerCellId.
        var portal = PortalPlane.FromVertices(
            new Vector3(45f, 40f, 45f),
            new Vector3(45f, 60f, 45f),
            new Vector3(45f, 60f, 55f),
            targetCellId: 0xFFFF, ownerCellId: 0x0100, flags: 0);

        engine.AddLandblock(0xA9B4FFFFu, terrain, new[] { cell }, new[] { portal },
            worldOffsetX: 0f, worldOffsetY: 0f);

        // Walk from X=40 (outdoor) through X=45 (portal) to X=50 (indoor).
        var result = engine.Resolve(
            new Vector3(40f, 50f, 50f), cellId: 0x0001, delta: new Vector3(10f, 0f, 0f),
            stepUpHeight: 5f);

        // Should have transitioned to indoor cell 0x0100.
        Assert.Equal(0x0100u, result.CellId & 0xFFFFu);
        Assert.True(result.IsOnGround);
    }

    [Fact]
    public void Resolve_IndoorThroughExitPortal_TransitionsToOutdoor()
    {
        var engine = new PhysicsEngine();
        var terrain = new TerrainSurface(FlatHeightmap(50), LinearHeightTable());

        var cellVerts = new Dictionary<ushort, Vector3>
        {
            [0] = new(40f, 40f, 50f),
            [1] = new(60f, 40f, 50f),
            [2] = new(60f, 60f, 50f),
            [3] = new(40f, 60f, 50f),
        };
        var cellPolys = new List<List<short>> { new() { 0, 1, 2, 3 } };
        var cell = new CellSurface(0x0100, cellVerts, cellPolys);

        // Same portal geometry — OwnerCellId = 0x0100, TargetCellId = 0xFFFF (outdoor exit).
        var portal = PortalPlane.FromVertices(
            new Vector3(45f, 40f, 45f),
            new Vector3(45f, 60f, 45f),
            new Vector3(45f, 60f, 55f),
            targetCellId: 0xFFFF, ownerCellId: 0x0100, flags: 0);

        engine.AddLandblock(0xA9B4FFFFu, terrain, new[] { cell }, new[] { portal },
            worldOffsetX: 0f, worldOffsetY: 0f);

        // Walk from X=50 (indoor) through X=45 (portal) to X=40 (outdoor).
        var result = engine.Resolve(
            new Vector3(50f, 50f, 50f), cellId: 0x0100, delta: new Vector3(-10f, 0f, 0f),
            stepUpHeight: 5f);

        // Should have transitioned to outdoor.
        Assert.True((result.CellId & 0xFFFFu) < 0x0100u);
        Assert.True(result.IsOnGround);
    }

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

        // Landblock A: flat at Z=50, offset at X=0.
        var terrainA = new TerrainSurface(FlatHeightmap(50), LinearHeightTable());
        engine.AddLandblock(0xA9B4FFFFu, terrainA, Array.Empty<CellSurface>(),
            Array.Empty<PortalPlane>(), worldOffsetX: 0f, worldOffsetY: 0f);

        // Landblock B: flat at Z=60, offset at X=192 (adjacent east).
        var terrainB = new TerrainSurface(FlatHeightmap(60), LinearHeightTable());
        engine.AddLandblock(0xAAB4FFFFu, terrainB, Array.Empty<CellSurface>(),
            Array.Empty<PortalPlane>(), worldOffsetX: 192f, worldOffsetY: 0f);

        // Walk from X=190 (landblock A) across to X=194 (landblock B).
        var result = engine.Resolve(
            new Vector3(190f, 96f, 50f), cellId: 0x0001, delta: new Vector3(4f, 0f, 0f),
            stepUpHeight: 15f);

        // Should be at Z=60 (landblock B's terrain) and position X≈194.
        Assert.Equal(60f, result.Position.Z, precision: 1);
        Assert.True(result.Position.X > 192f);
    }

    [Fact]
    public void Resolve_LeaveIndoorCell_TransitionsToOutdoor()
    {
        var engine = new PhysicsEngine();
        var terrain = new TerrainSurface(FlatHeightmap(50), LinearHeightTable());

        var cellVerts = new Dictionary<ushort, Vector3>
        {
            [0] = new(40f, 40f, 55f),
            [1] = new(60f, 40f, 55f),
            [2] = new(60f, 60f, 55f),
            [3] = new(40f, 60f, 55f),
        };
        var cellPolys = new List<List<short>> { new() { 0, 1, 2, 3 } };
        var cell = new CellSurface(0x0100, cellVerts, cellPolys);

        engine.AddLandblock(0xA9B4FFFFu, terrain, new[] { cell }, Array.Empty<PortalPlane>(),
            worldOffsetX: 0f, worldOffsetY: 0f);

        // Start inside the cell, walk out.
        var result = engine.Resolve(
            new Vector3(50f, 50f, 55f), cellId: 0x0100, delta: new Vector3(-20f, 0f, 0f),
            stepUpHeight: 10f);

        // Should transition back to outdoor.
        Assert.True(result.CellId < 0x0100u);
        Assert.Equal(50f, result.Position.Z, precision: 1);
        Assert.True(result.IsOnGround);
    }

    [Fact]
    public void Resolve_NoSurfaceUnderEntity_NotOnGround()
    {
        var engine = new PhysicsEngine();
        // No landblocks loaded — entity is floating in void.

        var result = engine.Resolve(
            new Vector3(0f, 0f, 100f), cellId: 0x0001, delta: Vector3.Zero,
            stepUpHeight: 2f);

        Assert.False(result.IsOnGround);
    }
}