SA1390 - Session ID regeneration on focus loss (#1392)

* Fixes #1390

* Clean up prior to PR

* Removed unused logging imports introduced during debugging

* Added mechanism to store the session ID seed temporarily during account creation

* Implemented keeping session ID on lose/regain focus via Hariss' better way using the savedInstanceState Bundle

* Removed now unused imports

app/src/main/java/org/thoughtcrime/securesms/onboarding/LandingActivity.kt

@@ -14,6 +14,11 @@ class LandingActivity : BaseActionBarActivity() {
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
+
+        // We always hit this LandingActivity on launch - but if there is a previous instance of
+        // Session then close this activity to resume the last activity from the previous instance.
+        if (!isTaskRoot) { finish(); return }
+
         val binding = ActivityLandingBinding.inflate(layoutInflater)
         setContentView(binding.root)
         setUpActionBarSessionLogo(true)

app/src/main/java/org/thoughtcrime/securesms/onboarding/RegisterActivity.kt

@@ -35,6 +35,8 @@ import javax.inject.Inject
 @AndroidEntryPoint
 class RegisterActivity : BaseActionBarActivity() {
 
+    private val temporarySeedKey = "TEMPORARY_SEED_KEY"
+
     @Inject
     lateinit var configFactory: ConfigFactory
 
@@ -77,13 +79,20 @@ class RegisterActivity : BaseActionBarActivity() {
         }, 61, 75, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE)
         binding.termsTextView.movementMethod = LinkMovementMethod.getInstance()
         binding.termsTextView.text = termsExplanation
-        updateKeyPair()
+        updateKeyPair(savedInstanceState?.getByteArray(temporarySeedKey))
+    }
+
+    override fun onSaveInstanceState(outState: Bundle) {
+        super.onSaveInstanceState(outState)
+        seed?.let { tempSeed ->
+            outState.putByteArray(temporarySeedKey, tempSeed)
+        }
     }
     // endregion
 
     // region Updating
-    private fun updateKeyPair() {
-        val keyPairGenerationResult = KeyPairUtilities.generate()
+    private fun updateKeyPair(temporaryKey: ByteArray?) {
+        val keyPairGenerationResult = temporaryKey?.let(KeyPairUtilities::generate) ?: KeyPairUtilities.generate()
         seed           = keyPairGenerationResult.seed
         ed25519KeyPair = keyPairGenerationResult.ed25519KeyPair
         x25519KeyPair  = keyPairGenerationResult.x25519KeyPair
@@ -125,7 +134,6 @@ class RegisterActivity : BaseActionBarActivity() {
         // which can result in an invalid database state
         database.clearAllLastMessageHashes()
         database.clearReceivedMessageHashValues()
-
         KeyPairUtilities.store(this, seed!!, ed25519KeyPair!!, x25519KeyPair!!)
         configFactory.keyPairChanged()
         val userHexEncodedPublicKey = x25519KeyPair!!.hexEncodedPublicKey