class Mutant::Repository::Diff

def diff_index(root)
  world
    .capture_command(%W[git diff-index #{to}])
    .bind do |status|
      Mutant
        .traverse(->(line) { parse_line(root, line) }, status.stdout.lines)
        .fmap do |paths|
          paths.to_h { |path| [path.path, path] }
        end
    end
end

def parse_line(root, line)
  match = FORMAT.match(line)
  if match
    Either::Right.new(
      Path.new(
        path:  root.join(Util.one(match.captures)),
        to:,
        world:
      )
    )
  else
    Either::Left.new("Invalid git diff-index line: #{line}")
  end
end

def repository_root
  world
    .capture_command(%w[git rev-parse --show-toplevel])
    .fmap { |status| world.pathname.new(status.stdout.chomp) }
end

def touched_path(path, &)
  touched_paths.from_right { |message| fail Error, message }.fetch(path, &)
end

def touched_paths
  repository_root.bind(&method(:diff_index))
end

def touches?(path, line_range)
  touched_path(path) { return false }
    .touches?(line_range)
end

def touches_path?(path)
  touched_path(path) { return false }
  true
end