var diskMap = File.ReadAllText("input.txt");
var disk = GenerateFileSystem(diskMap); // I could create a class for this, but... meh
var part1 = DefragBlocks(new List<int>(disk.Item1));
var part2 = DefragFiles(new List<int>(disk.Item1), new List<(int Id, int Length, int Position)>(disk.Item2), disk.Item3);

Console.WriteLine($"Part1: {part1}\nPart2: {part2}");

long DefragFiles(List<int> fileSystem, List<(int Id, int Length, int Position)> files, List<(int Length, int Position)> free)
{
    for (var i = files.Count - 1; i >= 0; i--)
    {
        var file = files[i];
        for (var j = 0; j < free.Count; j++)
        {
            var slot = free[j];
            if (file.Position < slot.Position)
            {
                break;
            }

            if (slot.Length >= file.Length)
            {
                for (var k = 0; k < file.Length; k++)
                {
                    (fileSystem[slot.Position + k], fileSystem[file.Position + k]) = (fileSystem[file.Position + k], fileSystem[slot.Position + k]);
                }

                free[j] = (slot.Length - file.Length, slot.Position + file.Length);

                break;
            }
        }
    }

    return CalculateChecksum(fileSystem);
}

long DefragBlocks(List<int> fileSystem)
{
    (int left, int right) = (0, fileSystem.Count - 1);
    while (left < right)
    {
        if (fileSystem[left] != -1)
        {
            left++;
        }
        else
        {
            if (fileSystem[right] == -1)
            {
                right--;
            }
            else
            {
                (fileSystem[left], fileSystem[right]) = (fileSystem[right], fileSystem[left]);
            }
        }
    }

    return CalculateChecksum(fileSystem);
}

long CalculateChecksum(List<int> fileSystem)
{
    var checksum = 0L;
    for (var i = 0; i < fileSystem.Count; i++)
    {
        var value = fileSystem[i];

        if (value != -1)
        {
            checksum += value * i;
        }

    }

    return checksum;
}

(List<int>, List<(int Id, int Length, int Position)>, List<(int Length, int Position)>) GenerateFileSystem(string diskMapDescription)
{

    var file = true;
    var fileSystem = new List<int>();
    var freeSpace = new List<(int Length, int Position)>();
    var files = new List<(int Id, int Length, int Position)>();
    var id = 0;

    foreach (var length in diskMapDescription.Select(c => int.Parse(c + "")))
    {
        var value = file ? id : -1;
        var position = fileSystem.Count;

        if (file)
        {
            files.Add((id, length, position));
            id += 1;
        }
        else
        {
            freeSpace.Add((length, position));
        }

        for (int i = 0; i < length; i++)
        {
            fileSystem.Add(value);
        }

        file = !file;
    }

    return (fileSystem, files, freeSpace);
}