module TelegramOnSteroids::Keyboard::Paginatable
  DEFAULT_PER_PAGE = 2

  def paginatable
    true
  end

  def to_telegram_format
    action.session.write(:current_page, current_page)
    return buttons if first_page? && last_page?

    buttons[offset...offset + per_page].push(navigation_buttons)
  end

  def navigation_buttons
    return [prev_button] if last_page?
    return [next_button] if first_page?

    [prev_button, next_button]
  end

  def per_page
    @per_page || DEFAULT_PER_PAGE
  end

  def per_page=(val)
    @per_page = val
  end

  def current_page
    return action.session.read(:current_page) || 1 unless request.params.callback_data =~ /page/

    request.params.callback_data.scan(/\d+/).first.to_i
  end

  def offset
    (current_page - 1) * per_page
  end

  def last_page?
    current_page * per_page >= buttons.size
  end

  def first_page?
    current_page == 1
  end

  def prev_button
    { text: '<< Prev', callback_data: "page_#{current_page - 1}" }
  end

  def next_button
    { text: 'Next >>', callback_data: "page_#{current_page + 1}" }
  end
end