firebase - Firestore: Version history of documents

Question

I'm looking for a proper way to structure Firestore database to handle multiple version histories of documents inside a single collection.

For example: I have a collection named offers which have multiple documents which correspond to multiple offers. For each of these documents, I'd like to have history of changes, something like changes on Google Docs.

Since documents support only adding fields directly or nesting another collection, here's a structure I had in mind:

collections: offers
 - documents: offer1, (offer2, offer3, ...)
     - fields populated with latest version of the offer content
     - nested collection named history
         - nested documents for each version (v1, v2, v3), which in turn have fields specifing state of each field in that version. 

This seems a bit overly complicated since I have latest state and than nested collection for history. Can this be somehow in flat structure where latest item in array is the latest state, or something similar.

Also, history state is generated on a button click, so I don't need every possible change saved in a history, just snapshots when user saves it.

I'd like to use Firebase as my DB for this, as I need it some other things, so I'm not looking into different solutions for now.

Thanks!

EDIT: According to the Alex's answer, here's my another take on this.

Firestore-root
   |
   --- offers (collection)
        |
        --- offerID (document)
        |   (with fields populated )
        |        |
        |        --- history (collection) //last edited timestamp
        |            |
        |            --- historyId
        |            --- historyId
        |
         --- offerID (document)
            (with fields populated with latest changes)
                 |
                 --- history (collection) //last edited timestamp
                     |
                     --- historyId
                     --- historyId

This way I can query whole offers collection and get array of offers together with latest status since it's on the same level as the collection itself. Then if I need specific content from history state, I can query history collection of specific offer and get it's history states. Does this make sense?

I'm not sure about denormalization as this seems like it solves my problem and avoids complication.

Once more, requirements are: - being able to fetch all offers with latest state (works) - being able to load specific history state (works)

Just every time I update history collection with new state, I overwrite the fields directly in offerID collection with the same, latest, state.

Am I missing something?

Answer 1

Waitting for answers