mongoDb: aggregate document references to subgroups - mongodb

Question

I've a set of BSON documents in a mongoDb collection which I want to process according to form cascading sub-documents. There are thousand of duplicate id's only to be differentiated by timestamps and documents with type subsystem-> component -> subcomponent; and they should be attached to each other based on source. This is a sample I currently have:
[{
"id": 1001,
"type": "subsystem",
"time": 1454767739,
"payload": {
"key": "..."
}
},
{
"id": 1001,
"type": "subsystem",
"time": 1454767539,
"payload": {
"key": "..."
}
},
{
"id": 2001,
"type": "component",
"time": 1454767778,
"source": 1001,
"payload": {
"key": "..."
}
},
{
"id": 5002,
"type": "subcomponent",
"time": 1454767779,
"source": 2001,
"payload": {
"key": "..."
}
},
{
"id": 5003,
"type": "subcomponent",
"time": 1454767798,
"source": 2001,
"payload": {
"key": "..."
}
}]
And what am I trying to do is this:
match all elements with a timestamp lower than a maxTime value
group all elements by (unique) id, but only use the newest value ($max: $time) for $$ROOT (every id is unique now)
group all by attribute source as a array to the element with that id (or _id)
I've achieved 1.) and 2.) already have this group:
[{
"_id": 1001,
"reftime": 1454767739,
"element": [
{
"id": 1001,
"type": "subsystem",
"time": 1454767739,
"payload": {
"key": "..."
}
}
]
},
{
"_id": 2001,
"reftime": 1454767778,
"element": [
{
"id": 2001,
"type": "component",
"time": 1454767778,
"source": 1001,
"payload": {
"key": "..."
}
}
]
},
{
"_id": 5002,
"reftime": 1454767779,
"element": [
{
"id": 5002,
"type": "subcomponent",
"time": 1454767779,
"source": 2001,
"payload": {
"key": "..."
}
}
]
},
{
"_id": 5003,
"reftime": 1454767798,
"element": [
{
"id": 5003,
"type": "subcomponent",
"time": 1454767798,
"source": 2001,
"payload": {
"key": "..."
}
}
]
}]
But what I want is the elements to be structured according to their links in the source value. So it would look something like this:
{
"_id": 1001,
"reftime": 1454767739,
"element": [
{
"id": 1001,
"type": "subsystem",
"time": 1454767739,
"payload": {
"key": "..."
}
}
],
"attached": [
{
"_id": 2001,
"reftime": 1454767778,
"element": [
{
"id": 2001,
"type": "component",
"time": 1454767778,
"source": 1001,
"payload": {
"key": "..."
}
}
],
"attached": [
{
"_id": 5002,
"reftime": 1454767779,
"element": [
{
"id": 5002,
"type": "subcomponent",
"time": 1454767779,
"source": 2001,
"payload": {
"key": "..."
}
}
]
},
{
"_id": 5003,
"reftime": 1454767798,
"element": [
{
"id": 5003,
"type": "subcomponent",
"time": 1454767798,
"source": 2001,
"payload": {
"key": "..."
}
}
]
}
]
}
]
}
Is this possible? I'm struggling to form a group with everything that has a source and combine this with the group from sample 2.). Or if that would help, I could introduce a source: 0? for every subsystem and group by that under a single root element?
Any ideas or insights? I'm currently stuck at this point. Thank you!