part1.ts

import * as fs from 'fs';
const input = fs.readFileSync('input', 'utf8');

const DIRECTION_MAP = [
	{ x: 1, y: 0 },
	{ x: 0, y: 1 },
	{ x: -1, y: 0 },
	{ x: 0, y: -1 },
];

const walk = (pos: { x: number; y: number; direction: number }, steps: number) => {
	for (; steps > 0; steps--) {
		const heading = DIRECTION_MAP[pos.direction];
		let next = { ...pos };
		next.x += heading.x;
		next.y += heading.y;
		if (maze[next.y]?.[next.x] !== '.' && maze[next.y]?.[next.x] !== '#') {
			next = wrap(pos);
		}
		if (maze[next.y][next.x] === '#') {
			break;
		}
		pos = next;
	}
	return pos;
};

const wrap = (pos: { x: number; y: number; direction: number }) => {
	const heading = DIRECTION_MAP[pos.direction];
	const opposite = { x: heading.x * -1, y: heading.y * -1 };
	const wrap = { ...pos };
	while (
		maze[wrap.y + opposite.y]?.[wrap.x + opposite.x] === '.' ||
		maze[wrap.y + opposite.y]?.[wrap.x + opposite.x] === '#'
	) {
		wrap.x += opposite.x;
		wrap.y += opposite.y;
	}
	return wrap;
};

let [maze, directions] = input.split('\n\n');
let pos = { x: 0, y: 0, direction: 0 };
maze = maze.split('\n');

directions = directions.replace(/(R|L)/g, ',$1,').split(',');
while (maze[pos.y][pos.x] !== '.') {
	pos.x++;
}
while (directions.length > 0) {
	const next = directions.shift();
	if (next === 'R') {
		pos.direction = (pos.direction + 1) % 4;
	} else if (next === 'L') {
		pos.direction = (4 + pos.direction - 1) % 4;
	} else if (Number.isInteger(+next)) {
		pos = walk(pos, +next);
	}
}

const result = (pos.y + 1) * 1000 + (pos.x + 1) * 4 + pos.direction;

console.log(result);