/** Grid math. Origin at world center, +x east, +y south, Dir 0..3 = N,E,S,W clockwise. */
import type { Dir, Vec2 } from '../contracts';

export const DIR_VEC: ReadonlyArray<Vec2> = [
  { x: 0, y: -1 }, // 0 N
  { x: 1, y: 0 },  // 1 E
  { x: 0, y: 1 },  // 2 S
  { x: -1, y: 0 }, // 3 W
];

export const GRID_MIN = -32;
export const GRID_MAX = 31;

/** Packs a tile into a unique number so occupancy can live in a flat Map. */
export function tileKey(x: number, y: number): number {
  return (x + 32768) * 65536 + (y + 32768);
}

export function inBounds(x: number, y: number): boolean {
  return x >= GRID_MIN && x <= GRID_MAX && y >= GRID_MIN && y <= GRID_MAX;
}

/** Footprint after rotation — facing E or W swaps width and height. */
export function footprintOf(fp: Vec2, dir: Dir): Vec2 {
  return dir === 1 || dir === 3 ? { x: fp.y, y: fp.x } : { x: fp.x, y: fp.y };
}