AdventOfCode23/Day15/InitializationStep.cs

using System.Text.RegularExpressions;

namespace Day15;

public partial class InitializationStep
{
    [GeneratedRegex(@"^(\w+)([=-])(\d+)?$")]
    private partial Regex InstructionMatcher();
    
    private readonly string _instruction;
    
    public string Label { get; }
    public char Operation { get; }
    public int? FocalLength { get; }

    public InitializationStep(string instruction)
    {
        _instruction = instruction;

        var match = InstructionMatcher().Match(_instruction);
        if (!match.Success)
        {
            throw new InvalidOperationException($"Invalid instruction {_instruction}");
        }

        Label = match.Groups[1].Value;
        Operation = match.Groups[2].Value[0];
        FocalLength = match.Groups[3].Success ? int.Parse(match.Groups[3].Value) : null;
    }

    public void Execute(List<List<Lens>> boxes)
    {
        var box = boxes[AsciiHash.Hash(Label)];
        switch (Operation)
        {
            case '=':
                var index = box.FindIndex(lens => lens.Label == Label);
                if (index >= 0)
                {
                    box[index] = new Lens(Label, FocalLength!.Value);
                }
                else
                {
                    box.Add(new Lens(Label, FocalLength!.Value));
                }
                break;
            case '-':
                box.RemoveAll(lens => lens.Label == Label);
                break;
        }
    }
    
    public byte GetHash()
    {
        return AsciiHash.Hash(_instruction);
    }
}