voxel/World.cs

using OpenTK.Mathematics;
using System.Collections.Generic;
using System.Drawing;

namespace Voxel
{
    public class World
    {
        private Dictionary<(int, int), Chunk> _chunks;

        private (int x, int z) _lastCenter = (0, 0);
        private int _loadDistance = 8;
        bool chunkLoadingInitialized = false;

        private static readonly Dictionary<Orientation, (int x, int y)> _neighborOffsets = new()
        {
            { Orientation.West, (1, 0) },
            { Orientation.East, (-1, 0) },
            { Orientation.North, (0, 1) },
            { Orientation.South, (0, -1) }
        };

        public World()
        {
            _chunks = new Dictionary<(int, int), Chunk>();
        }

        public Chunk GetChunk(int chunkX, int chunkZ)
        {
            _chunks.TryGetValue((chunkX, chunkZ), out Chunk chunk);
            return chunk;
        }

        public void AddChunk(Chunk chunk)
        {
            _chunks[(chunk.X, chunk.Y)] = chunk;

            UpdateNeighboringChunks(chunk);
            chunk.UpdateChunkMesh();
            Renderer.MarkBuffersDirty();
        }

        public void RemoveChunk(int chunkX, int chunkZ)
        {
            if (_chunks.TryGetValue((chunkX, chunkZ), out Chunk chunk))
            {
                var neighbors = GetChunkNeighbors(chunk).ToList();
                _chunks.Remove((chunkX, chunkZ));

                // 3. For each neighbor, remove reference to this chunk
                foreach (var (orientation, neighbor) in neighbors)
                {
                    var opposite = GetOppositeOrientation(orientation);
                    neighbor.Neighbors[opposite] = null;
                    neighbor.UpdateChunkMesh();
                }
            }
        }

        public new void UpdateChunkLoading(Vector3 playerPosition)
        {
            int centerX = (int)Math.Floor(playerPosition.X / Chunk.Size);
            int centerZ = (int)Math.Floor(playerPosition.Z / Chunk.Size);

            // Quick check - skip if still in same chunk
            if ((centerX == _lastCenter.x && centerZ == _lastCenter.z) && chunkLoadingInitialized)
                return;

            _lastCenter = (centerX, centerZ);

            // Calculate bounds
            int minX = centerX - _loadDistance;
            int maxX = centerX + _loadDistance;
            int minZ = centerZ - _loadDistance;
            int maxZ = centerZ + _loadDistance;

            // Unload chunks outside range
            UnloadDistantChunks(minX, maxX, minZ, maxZ);

            // Load chunks inside range
            LoadChunksInRange(minX, maxX, minZ, maxZ);

            chunkLoadingInitialized = true;
        }

        private void UnloadDistantChunks(int minX, int maxX, int minZ, int maxZ)
        {
            var chunksToRemove = new List<(int, int)>();

            foreach (var (chunkX, chunkZ) in _chunks.Keys)
            {
                if (chunkX < minX || chunkX > maxX || chunkZ < minZ || chunkZ > maxZ)
                {
                    chunksToRemove.Add((chunkX, chunkZ));
                }
            }

            foreach (var chunkPos in chunksToRemove)
            {
                RemoveChunk(chunkPos.Item1, chunkPos.Item2);
            }
        }

        private void LoadChunksInRange(int minX, int maxX, int minZ, int maxZ)
        {
            for (int x = minX; x <= maxX; x++)
            {
                for (int z = minZ; z <= maxZ; z++)
                {
                    if (!_chunks.ContainsKey((x, z)))
                    {
                        Chunk chunk = new Chunk(x, z);
                        AddChunk(chunk);
                    }
                }
            }
        }

        public void UpdateNeighboringChunks(Chunk chunk)
        {
            chunk.Neighbors[Orientation.West] = null;
            chunk.Neighbors[Orientation.East] = null;
            chunk.Neighbors[Orientation.North] = null;
            chunk.Neighbors[Orientation.South] = null;

            foreach (var (orientation, neighbor) in GetChunkNeighbors(chunk))
            {
                Orientation opposite = GetOppositeOrientation(orientation);
                neighbor.Neighbors[opposite] = chunk;
                chunk.Neighbors[orientation] = neighbor;
                neighbor.UpdateChunkMesh();
            }
        }

        private Orientation GetOppositeOrientation(Orientation orientation)
        {
            return orientation switch
            {
                Orientation.West => Orientation.East,
                Orientation.East => Orientation.West,
                Orientation.North => Orientation.South,
                Orientation.South => Orientation.North,
                _ => orientation
            };
        }

        public IEnumerable<Chunk> GetAllChunks()
        {
            return _chunks.Values;
        }

        public Blocks GetBlock(int worldX, int worldY, int worldZ)
        {
            var (chunkX, chunkZ, localX, localZ) = WorldToChunkCoords(worldX, worldZ);

            Chunk chunk = GetChunk(chunkX, chunkZ);
            if (chunk == null) return 0; // air if chunk not loaded

            return chunk.GetBlock(localX, worldY, localZ);
        }

        public void SetBlock(int worldX, int worldY, int worldZ, Blocks block)
        {
            var (chunkX, chunkZ, localX, localZ) = WorldToChunkCoords(worldX, worldZ);

            Chunk chunk = GetChunk(chunkX, chunkZ);
            if (chunk == null) return;

            chunk.SetBlock(localX, worldY, localZ, block);

            if (block == Blocks.Air && ((localX == Chunk.Size - 1 || localX == 0) || (localZ == Chunk.Size - 1 || localZ == 0)))
            {
                foreach (var orientation in GetEdgeOrientations(localX, localZ, Chunk.Size))
                {
                    if (chunk.Neighbors.TryGetValue(orientation, out var neighbor) && neighbor != null)
                    {
                        neighbor.UpdateChunkMesh();
                    }
                }
            }
        }

        public static (int chunkX, int chunkZ, int localX, int localZ) WorldToChunkCoords(int worldX, int worldZ)
        {
            int chunkX = worldX >= 0 ? worldX / Chunk.Size : (worldX + 1) / Chunk.Size - 1;
            int chunkZ = worldZ >= 0 ? worldZ / Chunk.Size : (worldZ + 1) / Chunk.Size - 1;

            int localX = ((worldX % Chunk.Size) + Chunk.Size) % Chunk.Size;
            int localZ = ((worldZ % Chunk.Size) + Chunk.Size) % Chunk.Size;

            return (chunkX, chunkZ, localX, localZ);
        }


        List<Orientation> GetEdgeOrientations(int localX, int localZ, int size)
        {
            var orientations = new List<Orientation>();

            if (localX == size - 1) orientations.Add(Orientation.West);
            if (localX == 0) orientations.Add(Orientation.East);
            if (localZ == size - 1) orientations.Add(Orientation.North);
            if (localZ == 0) orientations.Add(Orientation.South);

            return orientations;
        }

        public IEnumerable<(Orientation orientation, Chunk neighbor)> GetChunkNeighbors(Chunk chunk)
        {
            int chunkX = chunk.X;
            int chunkY = chunk.Y;

            foreach (var kv in _neighborOffsets)
            {
                Chunk neighbor = GetChunk(chunkX + kv.Value.x, chunkY + kv.Value.y);
                if (neighbor != null)
                    yield return (kv.Key, neighbor);
            }
        }

        public (bool success, Blocks block, int x, int y, int z, Vector3i normal) Raycast(Vector3 origin, Vector3 direction, float maxDistance)
        {
            int x = (int)MathF.Floor(origin.X);
            int y = (int)MathF.Floor(origin.Y);
            int z = (int)MathF.Floor(origin.Z);

            int stepX = direction.X > 0 ? 1 : -1;
            int stepY = direction.Y > 0 ? 1 : -1;
            int stepZ = direction.Z > 0 ? 1 : -1;

            float tDeltaX = direction.X != 0 ? MathF.Abs(1 / direction.X) : float.MaxValue;
            float tDeltaY = direction.Y != 0 ? MathF.Abs(1 / direction.Y) : float.MaxValue;
            float tDeltaZ = direction.Z != 0 ? MathF.Abs(1 / direction.Z) : float.MaxValue;

            float tMaxX = direction.X > 0 ? (MathF.Floor(origin.X) + 1 - origin.X) * tDeltaX
                : (origin.X - MathF.Floor(origin.X)) * tDeltaX;
            float tMaxY = direction.Y > 0 ? (MathF.Floor(origin.Y) + 1 - origin.Y) * tDeltaY
                : (origin.Y - MathF.Floor(origin.Y)) * tDeltaY;
            float tMaxZ = direction.Z > 0 ? (MathF.Floor(origin.Z) + 1 - origin.Z) * tDeltaZ
                : (origin.Z - MathF.Floor(origin.Z)) * tDeltaZ;

            float distance = 0f;
            Vector3i normal = Vector3i.Zero;

            while (distance <= maxDistance)
            {
                Blocks block = GetBlock(x, y, z);

                if (block != Blocks.Air)
                    return (true, block, x, y, z, normal);

                if (tMaxX < tMaxY && tMaxX < tMaxZ)
                {
                    x += stepX;
                    normal = new Vector3i(-stepX, 0, 0);
                    distance = tMaxX;
                    tMaxX += tDeltaX;
                }
                else if (tMaxY < tMaxZ)
                {
                    y += stepY;
                    normal = new Vector3i(0, -stepY, 0);
                    distance = tMaxY;
                    tMaxY += tDeltaY;
                }
                else
                {
                    z += stepZ;
                    normal = new Vector3i(0, 0, -stepZ);
                    distance = tMaxZ;
                    tMaxZ += tDeltaZ;
                }
            }

            return (false, Blocks.Air, 0, 0, 0, Vector3i.Zero);
        }

        public void Update()
        {

        }
    }
}