class Pagy

def series(size: @vars[:size])
  return [] if size.empty?
  raise VariableError.new(self, :size, 'to contain 4 items >= 0', size) \
        unless size.is_a?(Array) && size.size == 4 && size.all? { |num| !num.negative? rescue false } # rubocop:disable Style/RescueModifier
  # This algorithm is up to ~5x faster and ~2.3x lighter than the previous one (pagy < 4.3)
  left_gap_start  =     1 + size[0]   # rubocop:disable Layout/ExtraSpacing, Layout/SpaceAroundOperators
  left_gap_end    = @page - size[1] - 1
  right_gap_start = @page + size[2] + 1
  right_gap_end   = @last - size[3]
  left_gap_end    = right_gap_end  if left_gap_end   > right_gap_end
  right_gap_start = left_gap_start if left_gap_start > right_gap_start
  series          = []
  start           = 1
  if (left_gap_end - left_gap_start).positive?
    series.push(*start..(left_gap_start - 1), :gap)
    start = left_gap_end + 1
  end
  if (right_gap_end - right_gap_start).positive?
    series.push(*start..(right_gap_start - 1), :gap)
    start = right_gap_end + 1
  end
  series.push(*start..@last)
  series[series.index(@page)] = @page.to_s
  series
end