import { IRect } from '.';

export function grid_toWorld(
  cellSize: number,
  cx: number,
  cy: number
): [number, number] {
  return [(cx - 1) * cellSize, (cy - 1) * cellSize];
}

export function grid_toCell(
  cellSize: number,
  x: number,
  y: number
): [number, number] {
  return [Math.floor(x / cellSize) + 1, Math.floor(y / cellSize) + 1];
}

//grid_traverse * functions are based on "A Fast Voxel Traversal Algorithm for Ray Tracing",
//by John Amanides and Andrew Woo - http://www.cse.yorku.ca/~amana/research/grid.pdf
//It has been modified to include both cells when the ray "touches a grid corner",
//and with a different exit condition

export function grid_traverse_initStep(
  cellSize: number,
  ct: number,
  t1: number,
  t2: number
): [number, number, number] {
  const v: number = t2 - t1;

  if (v > 0) return [1, cellSize / v, ((ct + v) * cellSize - t1) / v];
  else if (v < 0)
    return [-1, -cellSize / v, ((ct + v - 1) * cellSize - t1) / v];
  else return [0, Number.MAX_SAFE_INTEGER, Number.MAX_SAFE_INTEGER];
}

export function grid_traverse(
  cellSize: number,
  x1: number,
  y1: number,
  x2: number,
  y2: number,
  traverseFunction: (cx: number, cy: number) => void
): void {
  const [cx1, cy1] = grid_toCell(cellSize, x1, y1);
  const [cx2, cy2] = grid_toCell(cellSize, x2, y2);
  let [stepX, dx, tx] = grid_traverse_initStep(cellSize, cx1, x1, x2);
  let [stepY, dy, ty] = grid_traverse_initStep(cellSize, cy1, y1, y2);
  let [cx, cy] = [cx1, cy1];

  traverseFunction(cx, cy);

  // The default implementation had an infinite loop problem when
  // approaching the last cell in some occassions. We finish iterating
  // when we are *next* to the last cell.
  do {
    if (tx < ty) {
      [tx, cx] = [tx + dx, cx + stepX];

      traverseFunction(cx, cy);
    } else {
      // Addition: include both cells when going through corners
      if (tx == ty) traverseFunction(cx + stepX, cy);

      ty = ty + dy;
      cy = cy + stepY;

      traverseFunction(cx, cy);
    }
  } while (Math.abs(cx - cx2) + Math.abs(cy - cy2) > 1);

  //If we have not arrived to the last cell, use it
  if (cx != cx2 || cy != cy2) traverseFunction(cx2, cy2);
}

export function grid_toCellRect(cellSize: number, rect: IRect): IRect {
  let [cx, cy] = grid_toCell(cellSize, rect.x, rect.y);

  const cr: number = Math.ceil((rect.x + rect.w) / cellSize);
  const cb: number = Math.ceil((rect.y + rect.h) / cellSize);

  return { x: cx, y: cy, w: cr - cx + 1, h: cb - cy + 1 };
}