import java.util.ArrayList;

public class ChunkManager {
  private static ArrayList<ArrayList<PhysicsObject>> chunks;
  private static int width;
  private static int height;
  private static int chunks_x;
  private static int chunks_y;

  public static void init(int width, int height, int chunks_x, int chunks_y) {
    ChunkManager.width = width;
    ChunkManager.height = height;
    ChunkManager.chunks_x = chunks_x;
    ChunkManager.chunks_y = chunks_y;
    ChunkManager.chunks = new ArrayList<ArrayList<PhysicsObject>>(chunks_x * chunks_y);
    ChunkManager.clear();
  }

  public static void clear() {
    chunks.clear();
    for (int i = 0; i < chunks_x * chunks_y; i++) {
      chunks.add(new ArrayList<PhysicsObject>());
    }
  }

  private static int[] to_chunk_coordinates(int x, int y) {
    return new int[] { (x * chunks_x) / width, (y * chunks_y) / height };
  }

  private static int get_chunk_index(int x, int y) {
    return x + (y * chunks_x);
  }

  private static int wrap(int index, int max) {
    int normalized = index;
    while (normalized < 0) {
      normalized += max;
    }
    return normalized % max;
  }

  public static void register(PhysicsObject obj) {
    int[] chunk = to_chunk_coordinates((int)obj.x, (int)obj.y);
    int index = get_chunk_index(chunk[0], chunk[1]);
    chunks.get(index).add(obj);
  }

  public static ArrayList<PhysicsObject> get_objects(int x, int y) {
    int[] chunk = to_chunk_coordinates(x, y);
    int[][] chunks = new int[][] {
      chunk,
      new int[] {wrap(chunk[0] + 1,chunks_x), chunk[1]},
      new int[] {wrap(chunk[0] - 1,chunks_x), chunk[1]},
      new int[] {wrap(chunk[0] + 1,chunks_x), wrap(chunk[1] + 1, chunks_y)},
      new int[] {wrap(chunk[0] - 1,chunks_x), wrap(chunk[1] + 1, chunks_y)},
      new int[] {wrap(chunk[0] + 1,chunks_x), wrap(chunk[1] - 1, chunks_y)},
      new int[] {wrap(chunk[0] - 1,chunks_x), wrap(chunk[1] - 1, chunks_y)},
      new int[] {chunk[0], wrap(chunk[1] + 1, chunks_y)},
      new int[] {chunk[0], wrap(chunk[1] - 1, chunks_y)}
    };
    ArrayList<PhysicsObject> objects = new ArrayList<PhysicsObject>();
    for (int[] c : chunks) {
      int index = get_chunk_index(c[0], c[1]);
      objects.addAll(ChunkManager.chunks.get(index));
    }
    return objects;
  }
}