class InvocaGems::Gemfile
  def initialize(path)
    @path = path
    @lines = File.readlines(path).map(&:chomp)
  end

  def find(gem_name, allow_missing: false)
    if index = @lines.find_index { |l| l =~ /\A\s*gem\s+.*[\'\"]#{gem_name}[\'\"]/ }
      InvocaGems::GemfileLine.new(self, @lines[index], index)
    else
      allow_missing or InvocaGems::Presenter.stop_with_message "could not find gem #{gem_name}"
      nil
    end
  end

  def append(gem_name)
    InvocaGems::GemfileLine.new(self, "gem '#{gem_name}'", -1)
  end

  def save!(gemspec)
    update_gemspec(gemspec)
    File.open(@path, "w") { |f| f.write(@lines.join("\n") + "\n") }
  end

  private

  def update_gemspec(gemspec)
    if gemspec.index == -1
      @lines << gemspec.line
    else
      @lines = @lines[0, gemspec.index] + [gemspec.line] + @lines[gemspec.index+1..-1]
    end
  end
end