module LdapEscape
  extend self

  FILTER = {
    "\u0000" => "\\00", # null
    "\u0028" => "\\28", # (
    "\u0029" => "\\29", # )
    "\u002a" => "\\2a", # *
    "\u005c" => "\\5c", # \
  }
  FILTER_REGEX = /(\0|\x28|\x29|\x2a|\x5c)/

  DN_BEGIN = {
    "\u0020" => "\\ ", # space
  }
  DN_BEGIN_REGEX = /^(\x20)/

  DN = {
    "\u0022" => "\\\"", # "
    "\u0023" => "\\#",  # #
    "\u002b" => "\\+",  # +
    "\u002c" => "\\,",  # ,
    "\u003b" => "\\;",  # ;
    "\u003c" => "\\<",  # <
    "\u003d" => "\\=",  # =
    "\u003e" => "\\>",  # >
    "\u005c" => "\\\\", # \
  }
  DN_REGEX = /(\x22|\x23|\x2b|\x2c|\x3b|\x3c|\x3d|\x3e|\x5c)/

  DN_END = {
    '\u0020' => "\\ ", # space
  }
  DN_END_REGEX = /(\x20)$/

  def filter(input : String) : String
    input.gsub(FILTER_REGEX) { |match| FILTER[match] }
  end

  def dn(input : String) : String
    input
      .gsub(DN_BEGIN_REGEX) { |match| DN_BEGIN[match] }
      .gsub(DN_REGEX) { |match| DN[match] }
      .gsub(DN_END_REGEX) { |match| DN_END[match] }
  end
end