class RuboCop::Cop::Style::SpaceBeforeBlockBraces

def autocorrect(range)
  lambda do |corrector|
    case range.source
    when /\s/ then corrector.remove(range)
    else           corrector.insert_before(range, ' ')
    end
  end
end

def on_block(node)
  return if node.loc.begin.is?('do') # No braces.
  # If braces are on separate lines, and the BlockDelimiters cop is
  # enabled, those braces will be changed to do..end by the user or by
  # auto-correct, so reporting space issues is not useful, and it
  # creates auto-correct conflicts.
  if config.for_cop('Style/BlockDelimiters')['Enabled'] &&
     block_length(node) > 0
    return
  end
  left_brace = node.loc.begin
  space_plus_brace = range_with_surrounding_space(left_brace)
  used_style =
    space_plus_brace.source.start_with?('{') ? :no_space : :space
  case used_style
  when style  then correct_style_detected
  when :space then space_detected(left_brace, space_plus_brace)
  else             space_missing(left_brace)
  end
end

def space_detected(left_brace, space_plus_brace)
  space = Parser::Source::Range.new(left_brace.source_buffer,
                                    space_plus_brace.begin_pos,
                                    left_brace.begin_pos)
  add_offense(space, space, 'Space detected to the left of {.') do
    opposite_style_detected
  end
end

def space_missing(left_brace)
  add_offense(left_brace, left_brace,
              'Space missing to the left of {.') do
    opposite_style_detected
  end
end