Restructuring a collection in MongoDB - mongodb

Question

My collection called "sets" currently looks like this:
[{
"_id": {
"$oid": "61c2c90b04a5c1fd873bca6c"
},
"exercise": "Flat Barbell Bench Press",
"repetitions": 8,
"rpe": 8,
"__v": 0,
"weight": 90,
"createdAt": {
"$date": {
"$numberLong": "1640155403594"
}
}
}]
It's an array with about 1500 documents several months worth of workouts.
What I'm trying to accomplish is this:
[{
"_id": {
"$oid": "62f3cee8d149f0c3534d848c"
},
"user": {
"$oid": "62d11eaa0caf6d2b3133b4b9"
},
"sets": [
{
"weight": 50,
"exercise": "Bench Press",
"repetitions": 8,
"rpe": 8,
"notes": "some note",
"_id": {
"$oid": "62f3cee8d149f0c3534d848d"
}
},
{},
{}
],
"createdAt": {
"$date": {
"$numberLong": "1660145384923"
}
}
}]
Essentially, what I'm trying to accomplish here is embedding an array of "set" objects as a field value for "sets" field. So that instead of a list of sets I have a list of workouts where sets are stored as an array of objects in a field called "sets".
Each "set" object has a date stamp and what I also need to do is to group these sets by day. So at the end of the day each new document represents one workout and has an id, user and sets fields, where each set is from that day.
My stackoverflow research tells me that I need to use aggregation, but I can't quite wrap my mind around how exactly I would do that.
Any help would be greatly appreciated!
/* UPDATE */
Here's the final query I came up with, hope someone will find it useful.
db.collection.aggregate([
{
$group: {
_id: {
$dateToString: {
format: "%Y-%m-%d",
date: "$createdAt"
}
},
sets: {
$push: {
_id: "$_id",
exercise: "$exercise",
repetitions: "$repetitions",
rpe: "$rpe",
__v: "$__v",
weight: "$weight",
createdAt: "$createdAt"
}
}
}
},
{
"$addFields": {
"user": "UserID",
"date": "$_id"
}
},
{
$project: {
"_id": 0
}
}
])