Validate a directive.
        :param directive: The directive to validate.
        :return: A tuple of action, patterns, thedir, dir_patterns

def _parse_directive(self, directive):
        """
        Validate a directive.
        :param directive: The directive to validate.
        :return: A tuple of action, patterns, thedir, dir_patterns
        """
        words = directive.split()
        if len(words) == 1 and words[0] not in ('include', 'exclude',
                                                'global-include',
                                                'global-exclude',
                                                'recursive-include',
                                                'recursive-exclude',
                                                'graft', 'prune'):
            # no action given, let's use the default 'include'
            words.insert(0, 'include')

        action = words[0]
        patterns = thedir = dir_pattern = None

        if action in ('include', 'exclude',
                      'global-include', 'global-exclude'):
            if len(words) < 2:
                raise DistlibException(
                    '%r expects <pattern1> <pattern2> ...' % action)

            patterns = [convert_path(word) for word in words[1:]]

        elif action in ('recursive-include', 'recursive-exclude'):
            if len(words) < 3:
                raise DistlibException(
                    '%r expects <dir> <pattern1> <pattern2> ...' % action)

            thedir = convert_path(words[1])
            patterns = [convert_path(word) for word in words[2:]]

        elif action in ('graft', 'prune'):
            if len(words) != 2:
                raise DistlibException(
                    '%r expects a single <dir_pattern>' % action)

            dir_pattern = convert_path(words[1])

        else:
            raise DistlibException('unknown action %r' % action)

        return action, patterns, thedir, dir_pattern