public static function get_conversation_counts_returns() {
        return new external_single_structure(
            [
                'favourites' => new external_value(PARAM_INT, 'Total number of favourite conversations'),
                'types' => new external_single_structure(
                    [
                        \core_message\api::MESSAGE_CONVERSATION_TYPE_INDIVIDUAL => new external_value(PARAM_INT,
                            'Total number of individual conversations'),
                        \core_message\api::MESSAGE_CONVERSATION_TYPE_GROUP => new external_value(PARAM_INT,
                            'Total number of group conversations'),
                        \core_message\api::MESSAGE_CONVERSATION_TYPE_SELF => new external_value(PARAM_INT,
                            'Total number of self conversations'),
                    ]
                ),
            ]
        );
    }