/** @file The mower: Logo-turtle moves on a yard of cells. */

/** what a model is told about a mower: its type, with the moves explained */
export const aboutMower = {
	ts: `interface Mower {
  /** put the mower down, facing north, and cut the cell under it */
  start(): Promise<void>;
  /** move forward one cell (10 yards), cutting the cell it enters */
  push(): Promise<void>;
  /** turn right 90 degrees, in place */
  turn(): Promise<void>;
  /** park the mower */
  stop(): Promise<void>;
}`,
};

const headings = [
	[0, -1], // north
	[1, 0], // east
	[0, 1], // south
	[-1, 0], // west
] as const;

/** a mower on a `width` × `height` yard, starting at `at`; pushing past an
 * edge wraps to the other side (6d) */
export const makeMower = ({ width, height, at }: { width: number; height: number; at: { x: number; y: number } }) => {
	let { x, y } = at;
	let heading = 0;
	const cut = new Set<string>();
	const cutHere = () => cut.add(`${x},${y}`);
	return {
		start() {
			heading = 0;
			cutHere();
		},
		push() {
			const [dx, dy] = headings[heading];
			x = (x + dx + width) % width;
			y = (y + dy + height) % height;
			cutHere();
		},
		turn() {
			heading = (heading + 1) % headings.length;
		},
		stop() {},
		cutCells: () => [...cut],
	};
};

export type Mower = ReturnType<typeof makeMower>;