module Puppet::Parser::Functions
  newfunction(:ensure_prefix, type: :rvalue, doc: <<-EOS
    This function ensures a prefix for all elements in an array or the keys in a hash.

    *Examples:*

      ensure_prefix({'a' => 1, 'b' => 2, 'p.c' => 3}, 'p.')

    Will return:
      {
        'p.a' => 1,
        'p.b' => 2,
        'p.c' => 3,
      }

      ensure_prefix(['a', 'p.b', 'c'], 'p.')

    Will return:
      ['p.a', 'p.b', 'p.c']
EOS
             ) do |arguments|
    if arguments.size < 2
      raise(Puppet::ParseError, 'ensure_prefix(): Wrong number of arguments ' \
        "given (#{arguments.size} for 2)")
    end

    enumerable = arguments[0]

    unless enumerable.is_a?(Array) || enumerable.is_a?(Hash)
      raise Puppet::ParseError, "ensure_prefix(): expected first argument to be an Array or a Hash, got #{enumerable.inspect}"
    end

    prefix = arguments[1] if arguments[1]

    if prefix
      unless prefix.is_a?(String)
        raise Puppet::ParseError, "ensure_prefix(): expected second argument to be a String, got #{prefix.inspect}"
      end
    end

    result = if enumerable.is_a?(Array)
               # Turn everything into string same as join would do ...
               enumerable.map do |i|
                 i = i.to_s
                 prefix && !i.start_with?(prefix) ? prefix + i : i
               end
             else
               Hash[enumerable.map do |k, v|
                 k = k.to_s
                 [prefix && !k.start_with?(prefix) ? prefix + k : k, v]
               end]
             end

    return result
  end
end