module Signet

def self.parse_auth_param_list auth_param_string
  # Production rules from:
  # http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-12
  token = /[-!#{$OUTPUT_RECORD_SEPARATOR}%&'*+.^_`|~0-9a-zA-Z]+/
  d_qdtext = /[\s\x21\x23-\x5B\x5D-\x7E\x80-\xFF]/n
  d_quoted_pair = /\\[\s\x21-\x7E\x80-\xFF]/n
  d_qs = /"(?:#{d_qdtext}|#{d_quoted_pair})*"/
  # Production rules that allow for more liberal parsing, i.e. single quotes
  s_qdtext = /[\s\x21-\x26\x28-\x5B\x5D-\x7E\x80-\xFF]/n
  s_quoted_pair = /\\[\s\x21-\x7E\x80-\xFF]/n
  s_qs = /'(?:#{s_qdtext}|#{s_quoted_pair})*'/
  # Combine the above production rules to find valid auth-param pairs.
  auth_param = /((?:#{token})\s*=\s*(?:#{d_qs}|#{s_qs}|#{token}))/
  auth_param_pairs = []
  last_match = nil
  remainder = auth_param_string
  # Iterate over the string, consuming pair matches as we go.  Verify that
  # pre-matches and post-matches contain only allowable characters.
  #
  # This would be way easier in Ruby 1.9, but we want backwards
  # compatibility.
  while (match = remainder.match auth_param)
    if match.pre_match && match.pre_match !~ /^[\s,]*$/
      raise ParseError,
            "Unexpected auth param format: '#{auth_param_string}'."
    end
    auth_param_pairs << match.captures[0] # Appending pair
    remainder = match.post_match
    last_match = match
  end
  if last_match.post_match && last_match.post_match !~ /^[\s,]*$/
    raise ParseError,
          "Unexpected auth param format: '#{auth_param_string}'."
  end
  # Now parse the auth-param pair strings & turn them into key-value pairs.
  (auth_param_pairs.each_with_object [] do |pair, accu|
    name, value = pair.split "=", 2
    case value
    when /^".*"$/
      value = value.gsub(/^"(.*)"$/, '\1').gsub(/\\(.)/, '\1')
    when /^'.*'$/
      value = value.gsub(/^'(.*)'$/, '\1').gsub(/\\(.)/, '\1')
    when %r{[()<>@,;:\\"/\[\]?={}]}
      # Certain special characters are not allowed
      raise ParseError,
            "Unexpected characters in auth param " \
            "list: '#{auth_param_string}'."
    end
    accu << [name, value]
  end)
end