using System.Numerics;
using AcDream.Core.World;
using DatReaderWriter.Types;

namespace AcDream.Core.Tests.World;

/// <summary>
/// Tests for SceneryGenerator: road-exclusion, loop bounds, building
/// suppression, and slope filter. The full Generate() pipeline requires
/// real dat files so behavior is tested via internal helpers.
/// </summary>
public class SceneryGeneratorTests
{
    // Terrain word layout (ushort):
    //   bits 0-1  = Road  (non-zero → on a road)
    //   bits 2-6  = TerrainType
    //   bits 11-15 = SceneType

    [Theory]
    [InlineData(0x0000, false)]  // no road bits
    [InlineData(0x0001, true)]   // road bit 0 set
    [InlineData(0x0002, true)]   // road bit 1 set
    [InlineData(0x0003, true)]   // both road bits set
    [InlineData(0x007C, false)]  // terrain type bits only, no road
    [InlineData(0xF800, false)]  // scenery bits only, no road
    [InlineData(0xF803, true)]   // road + scenery bits
    public void IsRoadVertex_CorrectlyIdentifiesRoadBits(ushort raw, bool expectedIsRoad)
    {
        Assert.Equal(expectedIsRoad, SceneryGenerator.IsRoadVertex(raw));
    }

    [Fact]
    public void IsRoadVertex_ZeroTerrain_IsNotRoad()
    {
        Assert.False(SceneryGenerator.IsRoadVertex(0));
    }

    [Fact]
    public void IsRoadVertex_MatchesTerrainInfoRoadProperty()
    {
        for (ushort raw = 0; raw < 4; raw++)
        {
            TerrainInfo ti = raw;
            bool expectedFromStruct = ti.Road != 0;
            bool actual = SceneryGenerator.IsRoadVertex(raw);
            Assert.True(actual == expectedFromStruct,
                $"raw=0x{raw:X4}: IsRoadVertex={actual} but TerrainInfo.Road={ti.Road}");
        }
    }

    // --- Edge vertex displacement tests ---
    // Retail iterates 9×9 vertices (0..8 on each axis). Vertices at x=8 or y=8
    // have base positions at 192 (= 8 * 24), which is AT the landblock boundary.
    // These produce valid scenery when displacement shifts them back into [0, 192).

    [Fact]
    public void DisplaceObject_EdgeVertex_CanProduceValidPosition()
    {
        // Vertex (3, 8): base_y = 8 * 24 = 192.
        // With DisplaceY > 0, some LCG seeds will produce negative displacement,
        // shifting the Y back below 192 into the valid range.
        var obj = new ObjectDesc
        {
            DisplaceX = 12f,
            DisplaceY = 12f,
            BaseLoc = new Frame { Origin = new Vector3(0, 0, 0) }
        };

        // Search across a range of global cell coords to find at least one
        // case where vertex y=8 displaces into [0, 192).
        bool foundValid = false;
        for (uint gx = 0; gx < 64 && !foundValid; gx++)
        {
            for (uint gy = 0; gy < 64 && !foundValid; gy++)
            {
                var localPos = SceneryGenerator.DisplaceObject(obj, gx, gy, 0);
                // Vertex (3, 8): cell corner at (3*24, 8*24) = (72, 192)
                float lx = 3 * 24f + localPos.X;
                float ly = 8 * 24f + localPos.Y;
                if (ly >= 0 && ly < 192f && lx >= 0 && lx < 192f)
                    foundValid = true;
            }
        }

        Assert.True(foundValid,
            "Expected at least one (globalCellX, globalCellY) where vertex y=8 " +
            "displaces back into [0, 192) — retail's 9×9 loop relies on this");
    }

    [Fact]
    public void DisplaceObject_InteriorVertex_AlwaysNearOrigin()
    {
        var obj = new ObjectDesc
        {
            DisplaceX = 12f,
            DisplaceY = 12f,
            BaseLoc = new Frame { Origin = new Vector3(0, 0, 0) }
        };

        // For interior vertices (x < 8, y < 8), displacement is bounded by
        // DisplaceX/Y (max 12 units each), so the result stays within one
        // cell of the origin.
        var localPos = SceneryGenerator.DisplaceObject(obj, 100, 100, 0);
        Assert.True(Math.Abs(localPos.X) <= 12f,
            $"Interior displacement X={localPos.X} exceeds DisplaceX=12");
        Assert.True(Math.Abs(localPos.Y) <= 12f,
            $"Interior displacement Y={localPos.Y} exceeds DisplaceY=12");
    }
}