class RuboCop::Cop::Style::RedundantRegexpCharacterClass

def backslash_b?(elem)
  # \b's behavior is different inside and outside of a character class, matching word
  # boundaries outside but backspace (0x08) when inside.
  elem == '\b'
end

def each_redundant_character_class(node)
  each_single_element_character_class(node) do |char_class|
    next unless redundant_single_element_character_class?(node, char_class)
    yield char_class.loc.body
  end
end

def each_single_element_character_class(node)
  node.parsed_tree&.each_expression do |expr|
    next if expr.type != :set || expr.expressions.size != 1
    next if expr.negative?
    next if %i[set posixclass nonposixclass].include?(expr.expressions.first.type)
    next if multiple_codepoints?(expr.expressions.first)
    yield expr
  end
end

def multiple_codepoints?(expression)
  expression.respond_to?(:codepoints) && expression.codepoints.count >= 2
end

def octal_requiring_char_class?(elem)
  # The octal escapes \1 to \7 only work inside a character class
  # because they would be a backreference outside it.
  elem.match?(/\A\\[1-7]\z/)
end

def on_regexp(node)
  each_redundant_character_class(node) do |loc|
    add_offense(
      loc, message: format(
        MSG_REDUNDANT_CHARACTER_CLASS,
        char_class: loc.source,
        element: without_character_class(loc)
      )
    ) do |corrector|
      corrector.replace(loc, without_character_class(loc))
    end
  end
end

def redundant_single_element_character_class?(node, char_class)
  class_elem = char_class.expressions.first.text
  non_redundant =
    whitespace_in_free_space_mode?(node, class_elem) ||
    backslash_b?(class_elem) || octal_requiring_char_class?(class_elem) ||
    requires_escape_outside_char_class?(class_elem)
  !non_redundant
end

def requires_escape_outside_char_class?(elem)
  REQUIRES_ESCAPE_OUTSIDE_CHAR_CLASS_CHARS.include?(elem)
end

def whitespace_in_free_space_mode?(node, elem)
  return false unless node.extended?
  /\s/.match?(elem)
end

def without_character_class(loc)
  without_character_class = loc.source[1..-2]
  # Adds `\` to prevent autocorrection that changes to an interpolated string when `[#]`.
  # e.g. From `/[#]{0}/` to `/#{0}/`
  loc.source == '[#]' ? "\\#{without_character_class}" : without_character_class
end