using System.Numerics;
using System.Security.Cryptography.X509Certificates;

// Main1();
Main2();

void Main1()
{
    var data = LoadData1(Path.Join("..", "..", "09a.txt"));
    int i = 0;
    int j = data.Length - 1;
    while (i < j)
    {
        if (data[i] == -1)
        {
            while (data[j] == -1)
                j--;
            data[i] = data[j];
            data[j] = -1;
        }
        i++;
    }
    i--;
    BigInteger checksum = 0;
    while (i >= 0)
    {
        if (data[i] < 0)
            throw new Exception($"Index {i} Value {data[i]}");
        checksum += i * data[i];
        i--;
    }
    Console.WriteLine($"Part1: {checksum,15}");
}

void Main2()
{
    var (files, empties) = LoadData2(Path.Join("..", "..", "09a.txt"));
    for (int i = files.Count-1; i >= 1; i--)
    {
        var file = files[i];
        for (int j = 0; j < empties.Count; j++)
        {
            var empty = empties[j];
            if (file.Location < empty.Location)
                break;
            if (file.Length <= empty.Length)
            {
                file.Location = empty.Location;
                empties[j] = new(empty.Location + file.Length, empty.Length - file.Length);
                break;
            }
        }
    }
    //long is big enough but changing it didn't help execution time so...
    BigInteger checksum = 0;
    foreach (var f in files)
    {
        for (int i = 0; i < f.Length; i++)
        {
            checksum += f.Id * (f.Location + i);
        }
    }
    Console.WriteLine($"Part2: {checksum,15}");
}

int[] LoadData1(string filepath)
{
    int next_id = 0;
    bool next_is_blank = false;
    int GetId()
    {
        if (next_is_blank)
        {
            next_is_blank = false;
            return -1;
        }
        else
        {
            next_is_blank = true;
            return next_id++;
        }
    }
    var data = File.ReadAllText(filepath).Trim().SelectMany(c => Enumerable.Repeat(GetId(), c - '0')).ToArray();
    return data;
}

(List<Filelike>,List<Empty>) LoadData2(string filepath)
{
    short next_id = 0;
    bool next_is_blank = false;
    int location = 0;
    List<Filelike> files = [];
    List<Empty> empties = [];
    foreach (char c in File.ReadAllText(filepath).Trim())
    {
        int length = c - '0';
        if (next_is_blank)
        {
            if (length > 0)
                empties.Add(new (location, length));
            next_is_blank = false;
            location += length;
        }
        else
        {
            next_is_blank = true;
            if (length > 0)
                files.Add(new (location, length, next_id));
            location += length;
            next_id++;
        }
    }
    return (files,empties);
}

class Filelike(int Location, int Length, short Id)
{
    public int Location = Location;
    public int Length = Length;
    public short Id = Id;
}
class Empty(int Location, int Length)
{
    public int Location = Location;
    public int Length = Length;
}

// class Filelike(int Location, int Length, int Id)
// {
//     public int Location = Location;
//     public int Length = Length;
//     public int Id = Id;
// }
// class Empty(int Location, int Length)
// {
//     public int Location = Location;
//     public int Length = Length;
// }