const fs = require('fs');

const input = fs.readFileSync(__dirname + '/input.txt', 'utf8');

interface MyFile { id: number, addr: number, size: number };

const freeSpaces: Array<{ addr: number, size: number }> = [];
const files: Array<MyFile> = [];
const reorderedFiles: Array<MyFile> = [];

let pointer = 0;
let id = 0;

for (let i = 0; i < input.length; i++) {
    const size = parseInt(input[i]);
    if (i % 2 === 0) {
        files.push({ id, size, addr: pointer });
        id++;
    } else if (size) {
        freeSpaces.push({ addr: pointer, size });
    }
    pointer += size;
}

const finalSpace = { addr: pointer, size: 0 };

if (input.length % 2 !== 0) {
    freeSpaces.push(finalSpace);
}

function printDisk() {
    const disk: Array<string> = [];
    files.forEach((file) => {
        for (let i = file.addr; i < file.addr + file.size; i++) {
            disk[i] = ''+file.id;
        }
    });
    reorderedFiles.forEach((file) => {
        for (let i = file.addr; i < file.addr + file.size; i++) {
            disk[i] = ''+file.id;
        }
    });
    freeSpaces.forEach((space) => {
        for (let i = space.addr; i < space.addr + space.size; i++) {
            disk[i] = '.';
        }
    });

    console.log(disk.join(''));
}
console.log(files);


while (true) {
    const lastFile = files.pop()!;
    let remainingSize = lastFile.size;
    console.log(files, lastFile, freeSpaces);
    while (remainingSize > 0) {
        const firstFreeSpace = freeSpaces.shift()!;
        let filePartSize;
        let remainingFreeSpace;
        if (remainingSize < firstFreeSpace.size) {
            filePartSize = remainingSize;
            remainingFreeSpace = firstFreeSpace.size - remainingSize;
        } else {
            filePartSize = firstFreeSpace.size;
            remainingFreeSpace = 0;
        }
        reorderedFiles.push({ addr: firstFreeSpace.addr, id: lastFile.id, size: filePartSize });
        finalSpace.size += filePartSize;
        finalSpace.addr -= filePartSize;
        remainingSize -= filePartSize;
        if (remainingFreeSpace) {
            freeSpaces.unshift({ addr: firstFreeSpace.addr + filePartSize, size: remainingFreeSpace });
        }
    }

    let i = freeSpaces.length - 2;
    if (!freeSpaces[i]) {
        break;
    }
    while (freeSpaces[i].addr + freeSpaces[i].size === finalSpace.addr) {
        finalSpace.addr = freeSpaces[i].addr;
        finalSpace.size += freeSpaces[i].size;
        freeSpaces[i] = finalSpace;
        freeSpaces.pop();
        i--;
    }
}

let checksum = 0;

const allFiles = files.concat(reorderedFiles);
allFiles.sort((a, b) => a.addr - b.addr);
console.log(allFiles, freeSpaces);

allFiles.forEach((file) => {
    for (let i = file.addr; i < file.addr + file.size; i++) {
        checksum += i * file.id;
    }
});

console.log(checksum);