feat: Migrate PreferencesManager to DataStore with Encrypted Storage

[PavloNetrebchuk]

Migrates PreferencesManager from SharedPreferences to Jetpack DataStore Preferences with AES-256-GCM encryption for sensitive data using Android Keystore.

DataStore Migration:

• Replaced SharedPreferences with DataStore
• Introduced type-safe preference keys using stringPreferencesKey, longPreferencesKey, booleanPreferencesKey
• Updated clearCorePreferences() and clearCalendarPreferences() to suspend functions
• Added androidx.datastore:datastore-preferences:1.2.0 dependency

Encryption Implementation:

• Created DataStoreEncryption class using Android Keystore + AES-256-GCM
• Encrypted sensitive fields:
  • accessToken
  • refreshToken
  • pushToken
  • user (JSON)
  • profile (JSON)

Security Details:

• Algorithm : AES-256-GCM
• Key Storage : Android Keystore (hardware-backed when available)
• IV Length : 2 bytes (random per encryption)
• Auth Tag : 128 bits
• Format : Base64(IV + ciphertext + auth_tag)

Motivation

SharedPreferences limitations:

• No encryption for sensitive data
• Synchronous API blocks the calling thread
• No type safety for keys

New implementation advantages:

• Sensitive tokens encrypted at rest
• Keys stored in Android Keystore (never exportable)
• Type-safe key definitions
• Guaranteed atomic writes

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[RawanMatar89]

@PavloNetrebchuk Will you please mention how this PR manage the migration for old user preferences ?

[RawanMatar89]

dataStore is async, so calling getValue on the main thread with runBlocking and dataStore could cause UI freeze.

[RawanMatar89]

all fun calls use "" as 'default value'.
keystore key can be invalidated if the user change device security settings or the system updated. so I think we should handle this senecio to prevent the case of using the app with an empty access token which will lead to bad user experience

[PavloNetrebchuk]

Hi @RawanMatar89
Thank you for the feedback.
I have already added changes according your messages:

Fix 1: runBlocking → runBlocking(Dispatchers.IO)
Both getValue and setValue now dispatch DataStore I/O to the IO thread pool, preventing potential deadlocks where DataStore's internal coroutine dispatcher conflicts with the calling thread.

Fix 2: Keystore invalidation handling

• scope (CoroutineScope(Dispatchers.IO + SupervisorJob())) for async cleanup
• Volatile anotation isKeyInvalidated flag to short-circuit after first detection
• In getEncryptedString(): if encrypted data exists but decrypt() returns "", the keystore key has been invalidated. The code sets the flag, clears core preferences, and sends LogoutEvent(true) via AppNotifier. This triggers
  AppViewModel.handleLogoutEvent() → clears DB → navigates to login screen.
• Constructor now takes AppNotifier as a second parameter.

Fix 3: SharedPreferences → DataStore migration

• shouldMigrate(): checks if old SharedPreferences (BuildConfig.APPLICATION_ID) has data
• migrate(): copies all old values to DataStore with:
  • Encryption of sensitive fields (access_token, refresh_token, push_token, user, account)
  • Key remapping for renamed keys (CALENDAR_ID → calendar_id, IS_RELATIVE_DATES_ENABLED → is_relative_dates_enabled, etc.)
  • Type-safe helpers for String/Long/Boolean migrations
• cleanUp(): clears the old SharedPreferences after successful migration

[RawanMatar89]

@PavloNetrebchuk, great efforts 👏🏻 LGTM 👍🏻