module Regexp::Syntax

def comparable(name)
  # add .99 to treat versions without a patch value as latest patch version
  Gem::Version.new((name.to_s.scan(/\d+/) << 99).join('.'))
end

def const_missing(const_name)
  if const_name =~ VERSION_CONST_REGEXP
    return fallback_version_class(const_name)
  end
  super
end

def fallback_version_class(version)
  sorted = (specified_versions + [version]).sort_by { |ver| comparable(ver) }
  index = sorted.index(version)
  index > 0 && const_get(sorted[index - 1])
end

def for(name)
  (@alias_map ||= {})[name] ||= version_class(name)
end

def new(name)
  warn 'Regexp::Syntax.new is deprecated in favor of Regexp::Syntax.for. '\
       'It does not return distinct instances and will be removed in v3.0.0.'
  self.for(name)
end

def specified_versions
  constants.select { |const_name| const_name =~ VERSION_CONST_REGEXP }
end

def supported?(name)
  name =~ VERSION_REGEXP && comparable(name) >= comparable('1.8.6')
end

def version_class(version)
  return Regexp::Syntax::Any if ['*', 'any'].include?(version.to_s)
  version =~ VERSION_REGEXP || raise(InvalidVersionNameError, version)
  version_const_name = "V#{version.to_s.scan(/\d+/).join('_')}"
  const_get(version_const_name) || raise(UnknownSyntaxNameError, version)
end