AdventOfCode23/Day1/FilePipeline.cs

using System.Text.RegularExpressions;

namespace Day1;

public partial class FilePipeline
{
    private readonly string _fileName;
    private readonly IStringTransform[] _transforms;

    public FilePipeline(string fileName, params IStringTransform[] transforms)
    {
        _fileName = fileName;
        _transforms = transforms;
    }

    public IEnumerable<int> Extract()
    {
        using var reader = File.OpenText(_fileName);
        while (!reader.EndOfStream)
        {
            var line = reader.ReadLine();
            var result = _transforms.Aggregate(line!, (prev, transform) => transform.Transform(prev));
            
            if (result.Length < 1)
            {
                throw new InvalidOperationException($"Not enough digits: '{line}'");
            }
            yield return int.Parse(new string(new char[] { result.First(), result.Last() }));
        }
    }

}