class RuboCop::Cop::Style::TrailingBlankLines

def autocorrect(range)
  @corrections << lambda do |corrector|
    corrector.replace(range, style == :final_newline ? "\n" : "\n\n")
  end
end

def investigate(processed_source)
  sb = processed_source.buffer
  return if sb.source.empty?
  whitespace_at_end = sb.source[/\s*\Z/]
  blank_lines = whitespace_at_end.count("\n") - 1
  wanted_blank_lines = style == :final_newline ? 0 : 1
  return unless blank_lines != wanted_blank_lines
  begin_pos = sb.source.length - whitespace_at_end.length
  autocorrect_range = Parser::Source::Range.new(sb, begin_pos,
                                                sb.source.length)
  begin_pos += "\n".length unless whitespace_at_end.length == 0
  report_range = Parser::Source::Range.new(sb, begin_pos,
                                           sb.source.length)
  add_offense(autocorrect_range, report_range,
              message(wanted_blank_lines, blank_lines))
end

def message(wanted_blank_lines, blank_lines)
  case blank_lines
  when -1
    'Final newline missing.'
  when 0
    'Trailing blank line missing.'
  else
    instead_of = if wanted_blank_lines == 0
                   ''
                 else
                   "instead of #{wanted_blank_lines} "
                 end
    format('%d trailing blank lines %sdetected.', blank_lines,
           instead_of)
  end
end