using System;

using System.Net.Http;

using System.Collections.Generic;

using System.Linq;

​

// Get data

var response = await new HttpClient().GetStringAsync("https://tompafireadventofcode.free.beeceptor.com/day5");

​

var lines = response.Split("\n").Select(line =>

{

    var parts = line.Split(" -> ");

​

    var coordinate1Parts = parts.First().Split(',').Select(int.Parse);

    var coordinate2Parts = parts.Last().Split(',').Select(int.Parse);

​

    var coordinate1 = new Coordinate(coordinate1Parts.First(), coordinate1Parts.Last());

    var coordinate2 = new Coordinate(coordinate2Parts.First(), coordinate2Parts.Last());

​

    return new Line(coordinate1, coordinate2);

});

​

// Part 1

​

var straightLines = lines.Where(line =>

    line.Start.X == line.End.X ||

    line.Start.Y == line.End.Y

    ).ToList();

​

var pointsCovered = straightLines.SelectMany(line => GetPointsCovered(line));

var pointsWithAtLeast2Crossings = pointsCovered.GroupBy(c => c).Count(x => x.Count() >= 2);

​

Console.WriteLine(pointsWithAtLeast2Crossings);

​

// Part 2

​

var straightOrDiagonalLines = lines.Where(line =>

    line.Start.X == line.End.X ||

    line.Start.Y == line.End.Y ||

    Math.Abs(line.End.X - line.Start.X) == Math.Abs(line.End.Y - line.Start.Y)

    ).ToList();

​

var pointsCoveredPart2 = straightOrDiagonalLines.SelectMany(line => GetPointsCovered(line));

var pointsWithAtLeast2CrossingsPart2 = pointsCoveredPart2.GroupBy(c => c).Count(x => x.Count() >= 2);

​

Console.WriteLine(pointsWithAtLeast2CrossingsPart2);

​

​

IEnumerable<Coordinate> GetPointsCovered(Line line)

{

    Func<int, int> operationX = line switch

    {

        { } when line.Start.X < line.End.X => v => ++v,

        { } when line.Start.X > line.End.X => v => --v,

        _ => v => v

    };

​

    Func<int, int> operationY = line switch

    {

        { } when line.Start.Y < line.End.Y => v => ++v,

        { } when line.Start.Y > line.End.Y => v => --v,

        _ => v => v

    };

​

    var current = line.Start;

​

    while (true)

    {

        yield return current;

​

        if (current == line.End)

        {

            break;

        }

​

        current = current with { X = operationX(current.X), Y = operationY(current.Y) };

    }

}

​

public record struct Coordinate(int X, int Y);

​

public record struct Line(Coordinate Start, Coordinate End);