part1.ts

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

let result = 0;

const rows = input.length;
const cols = input[0].length;

const startingRow = input.findIndex((row) => row.includes('S'));
const startingCol = input[startingRow].indexOf('S');

const canGoUp = ['|', '7', 'F'].includes(input[startingRow - 1][startingCol]);
const canGoDown = ['|', 'L', 'J'].includes(input[startingRow + 1][startingCol]);
const canGoLeft = ['-', 'L', 'F'].includes(input[startingRow][startingCol - 1]);
const canGoRight = ['-', '7', 'J'].includes(input[startingRow][startingCol + 1]);

let direction = 0; // up, right, down, left

if (canGoUp && canGoDown) {
	direction = 0;
} else if (canGoUp && canGoRight) {
	direction = 0;
} else if (canGoUp && canGoLeft) {
	direction = 0;
} else if (canGoDown && canGoRight) {
	direction = 2;
} else if (canGoDown && canGoLeft) {
	direction = 2;
} else if (canGoLeft && canGoRight) {
	direction = 1;
}

const rowDirections = [-1, 0, 1, 0];
const colDirections = [0, 1, 0, -1];

let row = startingRow;
let col = startingCol;

while (true) {
	result++;
	row += rowDirections[direction];
	col += colDirections[direction];
	switch (input[row][col]) {
		case 'L':
		case '7':
			direction ^= 3;
			break;
		case 'J':
		case 'F':
			direction ^= 1;
			break;
	}

	if (row == startingRow && col == startingCol) {
		break;
	}
}

console.log(Math.floor(result / 2));