using MoreLinq.Extensions;

namespace AOC2021;

/// <summary>
/// Day 13: <a href="https://adventofcode.com/2021/day/13"/>
/// </summary>
public sealed class Day13() : Day(2021, 13, "Transparent Origami")
{
    private List<(int x, int y)>? _dots;
    private List<(char axis, int index)>? _folds;

    public override void ProcessInput()
    {
        var s = Input.Split("").ToList();

        _dots = s[0].Select(p =>
        {
            var i = p.Split(',', 2).Select(int.Parse).ToList();
            return (i[0], i[1]);
        }).ToList();

        _folds = s[1].Select(p => p.Split(' ').Skip(2).First()).Select(p =>
        {
            var i = p.Split('=', 2);
            return (i[0][0], int.Parse(i[1]));
        }).ToList();
    }

    private static List<(int x, int y)> DoFold(List<(int x, int y)> grid, char axis, int at)
    {
        List<(int, int)> result = [];

        switch (axis)
        {
            case 'x':
                foreach (var (x, y) in grid) result.Add((x > at ? 2 * at - x : x, y));
                break;
            case 'y':
                foreach (var (x, y) in grid) result.Add((x, y > at ? 2 * at - y : y));
                break;
            default: throw new ArgumentException("invalid fold axis", nameof(axis));
        }

        return result.Distinct().ToList();
    }

    private string PrintGrid()
    {
        var xMax = _dots!.Max(g => g.x);
        var yMax = _dots!.Max(g => g.y);
        var s = new StringBuilder();

        for (var y = 0; y <= yMax; y++)
        {
            for (var x = 0; x <= xMax; x++)
                s.Append(_dots!.Contains((x, y)) ? "█" : "▒");

            if (y < yMax) s.AppendLine();
        }

        return s.ToString();
    }

    public override object Part1() =>
        DoFold(_dots!, _folds![0].axis, _folds[0].index).Count;

    public override object Part2()
    {
        foreach (var (axis, at) in _folds!)
            _dots = DoFold(_dots!, axis, at);

        return PrintGrid();
    }
}