require 'stringio'

module Net::BER::Extensions::String
  ##
  # Converts a string to a BER string. Universal octet-strings are tagged
  # with 0x04, but other values are possible depending on the context, so we
  # let the caller give us one.
  #
  # User code should call either #to_ber_application_string or
  # #to_ber_contextspecific.
  def to_ber(code = 0x04)
    [code].pack('C') + length.to_ber_length_encoding + self
  end

  ##
  # Creates an application-specific BER string encoded value with the
  # provided syntax code value.
  def to_ber_application_string(code)
    to_ber(0x40 + code)
  end

  ##
  # Creates a context-specific BER string encoded value with the provided
  # syntax code value.
  def to_ber_contextspecific(code)
    to_ber(0x80 + code)
  end

  ##
  # Nondestructively reads a BER object from this string.
  def read_ber(syntax = nil)
    StringIO.new(self).read_ber(syntax)
  end
  
  ##
  # Destructively reads a BER object from the string. 
  def read_ber!(syntax = nil)
    io = StringIO.new(self)

    result = io.read_ber(syntax)
    self.slice!(0...io.pos)
    
    return result
  end
end