class TestFileFinder::FileFinder

  def initialize(paths: [])
    @paths = [paths].flatten
  end

  def test_files
    search
  end

  private

  attr_reader :paths

  def search
    file_path_guesses.select { |path| File.exist?(path) }
  end

  def file_path_guesses
    paths.map do |path|
      guess_test_files_for(path)
    end.compact.uniq
  end

  def context
    {
      app:      %r{^app/(.+)\.rb$},
      lib:      %r{^lib/(.+)\.rb$},
      spec:     %r{^spec/(.+)_spec.rb$},
      spec_dir: 'spec',
    }
  end

  def guess_test_files_for(path)
    if (match = context[:app]&.match(path))
      return "#{context[:spec_dir]}/#{match[1]}_spec.rb"
    end

    if (match = context[:lib]&.match(path))
      return "#{context[:spec_dir]}/lib/#{match[1]}_spec.rb"
    end

    if context[:spec]&.match(path)
      return path
    end
  end
end