AoC day 9 part 2 solution

const fs = require('fs');

const data = fs
    .readFileSync('./input.txt')
    .toString()
    .trim()
    .replace(/\r/g, '')
    .split('')
    .map(Number);

const unpackedDisk = [];

for (let i = 0; i < data.length; i++) {
    const file = [];
    for (let j = data[i]; j > 0; j--) {
        if (i % 2 === 0) {
            file.push(i / 2);
        } else {
            file.push('.');
        }
    }
    if (file.length) {
        unpackedDisk.push(file);
    }
}

// defrag
const movedIds = [];
outer: for (let i = unpackedDisk.length - 1; i >= 0; i--) {
    if (unpackedDisk[i][0] !== '.' && !movedIds.includes(unpackedDisk[i][0])) {
        for (let j = 0; j <= i; j++) {
            if (
                unpackedDisk[j][0] === '.' &&
                unpackedDisk[j].length >= unpackedDisk[i].length
            ) {
                if (unpackedDisk[j].length === unpackedDisk[i].length) {
                    movedIds.push(unpackedDisk[i][0]);
                    let temp = [...unpackedDisk[j]];
                    unpackedDisk[j] = unpackedDisk[i];
                    unpackedDisk[i] = temp;
                    continue outer;
                } else {
                    movedIds.push(unpackedDisk[i][0]);
                    const temp = [...unpackedDisk[i]];
                    unpackedDisk[i].fill('.');
                    unpackedDisk.splice(
                        j,
                        1,
                        temp,
                        unpackedDisk[j].toSpliced(0, unpackedDisk[i].length)
                    );
                    i++;
                    continue outer;
                }
            }
        }
    }
}

const defraggedDisk = unpackedDisk.flat();

let checksum = 0;

defraggedDisk.forEach((block, id) => {
    if (block !== '.') {
        checksum += block * id;
    }
});

console.log(checksum);