Offline scan & contribution proposal (partially implemented)

[rudrankriyam]

Checklist

• [x] Bug Report - Reference #35 #34

Summary:

Motivation

• Making the application offline means that we provide essentially identical User experience, irrespective of the network condition.
• If a User finds an interesting or exotic product to add to the database, slow or no internet connectivity will disrupt the flow.
• This project will resolve the two unsolved features offline mode for consultation and offline mode for contribution, bringing us closer to launching version 1.0.

Objective

• A small version of the database comprised of key data only, to be downloaded during initialisation.
• It will later require synchronisation with the back-end to reconcile the updates regularly when there is a strong internet connection (preferably over WiFi connection).
• There will also be an option in the Setting screen to manually/automatically sync this database. While scanning products, key data about them (if recognized) should be shown instantly, even if there's no network.
• The full data of the history of the scanned products should be saved locally on the device. While offline (e.g. in a store with no network), users need to be able to scan and take photos for lots of products.
• Photos should be sent when network becomes available.

Technical Details

• A small copy of Realm client-side database allows to interact with synced data, which will be stored locally.
• The key data can be stored in a bundled Realm file to get the data.
• Realm has built-in offline capabilities and will queue any data changes to be sent to the server.
• The full data of history can be stored in a bundled Realm file to present the data. There is already a Swift file to show the history which will now be linkeds with the offline stored database.
• One solution would be to have a per-device realm that could be used as an image upload queue with a single class.

  class Image : RealmObject { 
  Byte[ ] Data 
  }

• Then, the objects with images will look like

  class ObjectWithImage : RealmObject { 
  string ImageUrl 
  }

• When a new ObjectWithImage is added, a corresponding Image object is added to the image Realm. Then, on the server, when a new Image gets synchronized, update the corresponding ObjectWithImage's ImageUrl.

Screenshots:

[teolemon]

This feature has been partially implemented (both scanning and contributing). I like the idea to be able to disable database update if you're not on WiFi, we could create a separate bug with it and close this one.