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ADR#8 Backup and sync (WIP).md

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ADR#8: Backup & Sync 🚧

To have a top-notch UX without the Ivy Cloud (own backend) we need to support:

  • Automatic offline backups. (mandatory)
  • Automatic Google Drive backups. (user's choice)
  • Sharing between multiple users and devices.
  • No lag/delays when creating transactions.

Solution

Backup Algorithm

  1. Export the database entities + user settings as one big JSON.
{
    "accounts": [
        ...
    ],
    "categories": [
        ...
    ],
    "transactions": [
        ...
    ],
    "settings": [
        ...
    ]
}

  1. Create a backup JSON file and ZIP it to reduce it's size.

  2. Saved the backup JSON zip to the local file-system

  3. (optional) Upload the backup JSON to user's personal Google Drive in "/Ivy-Wallet/backups/ivy-wallet-backup-json.zip".

⚠️ When this backup must be triggered?

Option A): After every write to app's Room Database

  • Pros
    • Google Drive backup will always be up-to-date.
    • even with many transactions the backup file is <1 MB and the operation is quite fast <1 second.
  • Cons
    • If user accidentally deletes an account in the app, the backup file will be automatically corrupted.
    • When making multiple transactions & edits the app will consume enourmous resources!
    • The app may lag

Option B): WorkManager - scheduled task every X hours

  • Pros
    • The app won't lag, won't consume extra resources.
    • Elegant and easy to implement solution.
  • Cons
    • Data between backups may be lost (not a big deal).
    • Might have Android background work restrictions problems.
    • Will wake-up phone's CPU => consume battery.
    • No "real-time" sync if multiple users/device use a shared backup file.

Option C) Work manager + trigger backup on app close or X seconds debounce after the last write to DB

  • Pros
    • Elegant like Option B)
    • Solves the "real-time" sync problem
    • Doesn't consume much resources!
  • Cons
    • Harder to implement
    • The backup operation may not finish if they user closes the app before the X debounce seconds
    • Will consume more resources if the X debounce seconds are low.

Sync Algorithm

Sync will only happen if the Google Drive integraiton is enabled.

Note: The sync must support multiple users and devices using the same backup JSON file

  1. App opens
  2. Fetch the latest "ivy-wallet-backup-json.zip"
  3. Merge the data using IDs and accepting as newer the ones with greatest last_synced in UTC (!!! last_synced must be added to each item in the DB)

Actions required

  • add last_synced to each item that will be backuped
  • don't backup user's settings because different users might want different settings

Architecture

  • :drive - drive agnostic API for mountint + CRUD files on user's personal drive, support only Google Drive (:drive:google-drive) for v1.

  • :android:file-system - Android specific logic and permission handling for reading/writing files on user's device including public directories.

  • :backup - exports/imports users data using JSON backup .zip (:backup:old imports JSON backup from the prod app) and the rest will work only with the dev verison.

    • does local file-system backup + Google Drive (user's preference)
    • automatic backups uses user-preferred file-system location
    • imports JSON backup .zip files for the old and new app
    • exports a JSON backup to user's chosen location when manually requests

  • :sync - implement the Sync algorithm and is responsible for merging local app's Room DB + the latest backup JSON from the Drive