Mongo query with sorted subDocument

gistfile1.txt

db.getCollection('test').aggregate([{$match: {name: "item6"}},{$unwind: '$slots'}, {$sort: {"slots.date": -1}},
{$group: {_id: '$_id',root: { $mergeObjects: '$$ROOT' }, slots: {$push: '$slots'}}}, { "$limit": 1 }, {
                    $replaceRoot: {
                        newRoot: {
                            $mergeObjects: ['$root', '$$ROOT']
                        }
                    }
                }, {
                    $project: {
                        root: 0 
                    }
                }])