Puppet::Parser::Functions.newfunction(
  :fqdn_rand_string,
  :arity => -2,
  :type => :rvalue,
  :doc => <<-DOC
  @summary
    Generates a random alphanumeric string. Combining the `$fqdn` fact and an
    optional seed for repeatable randomness.

  Optionally, you can specify a character set for the function (defaults to alphanumeric).

  Arguments
  * An integer, specifying the length of the resulting string.
  * Optionally, a string specifying the character set.
  * Optionally, a string specifying the seed for repeatable randomness.

  @return [String]

  @example Example Usage:
    fqdn_rand_string(10)
    fqdn_rand_string(10, 'ABCDEF!@$%^')
    fqdn_rand_string(10, '', 'custom seed')
  DOC
) do |args|
  raise(ArgumentError, 'fqdn_rand_string(): wrong number of arguments (0 for 1)') if args.empty?
  Puppet::Parser::Functions.function('is_integer')
  raise(ArgumentError, 'fqdn_rand_string(): first argument must be a positive integer') unless function_is_integer([args[0]]) && args[0].to_i > 0
  raise(ArgumentError, 'fqdn_rand_string(): second argument must be undef or a string') unless args[1].nil? || args[1].is_a?(String)

  Puppet::Parser::Functions.function('fqdn_rand')

  length = args.shift.to_i
  charset = args.shift.to_s.chars.to_a

  charset = (0..9).map { |i| i.to_s } + ('A'..'Z').to_a + ('a'..'z').to_a if charset.empty?

  rand_string = ''
  for current in 1..length # rubocop:disable Style/For : An each loop would not work correctly in this circumstance
    rand_string << charset[function_fqdn_rand([charset.size, (args + [current.to_s]).join(':')]).to_i]
  end

  rand_string
end