[{"uuid":"yxcvb","product":"[{\"pid\":\"4f76c06825aa486db9a7a5cedbc2ea19\",\"size\":\"S\"},{\"pid\":\"d3055e0a1bb040dba65674b9733bf4ce\",\"size\":\"M\"}]","timestamp":{"$date":"2023-01-01T11:25:47+00:00"}},{"uuid":"asdfg","product":"[{\"pid\":\"369b33cc768d496193b18d657d706920\",\"size\":\"M\"}]","timestamp":{"$date":"2023-01-02T11:25:47+00:00"}},{"uuid":"qwert","product":"[{\"pid\":\"13325cb71fd7413c8f3e18caf20b5d6d\",\"size\":\"S\"},{\"pid\":\"ac431397d49d449cab44d98dc13ec57c\",\"size\":\"M\"},{\"pid\":\"ba35b9f804a44e15bf197d3ef671dc34\",\"size\":\"L\"}]","timestamp":{"$date":"2023-01-03T11:25:47+00:00"}}]

db.collection.aggregate([{"$set":{"product":{"$function":{"body":"function(product) {return JSON.parse(product)}","args":["$product"],"lang":"js"}}}},{"$unwind":"$product"},{$group:{_id:{week:{"$isoWeek":"$timestamp"},size:"$product.size"},count:{$sum:1}}},{$sort:{"_id.week":-1}}])