Prevent the creation of 'weak' PINs.

Simple checks to prevent the same number, or sequentially
increasing/decreasing PINs. e.g. 1111, 1234, 54321, etc.

app/src/main/java/org/thoughtcrime/securesms/lock/v2/CreateKbsPinFragment.java

@@ -1,15 +1,20 @@
 package org.thoughtcrime.securesms.lock.v2;
 
-import android.view.View;
+import android.view.animation.Animation;
+import android.view.animation.TranslateAnimation;
+import android.widget.EditText;
+import android.widget.Toast;
 
 import androidx.annotation.NonNull;
 import androidx.annotation.PluralsRes;
 import androidx.autofill.HintConstants;
+import androidx.core.content.ContextCompat;
 import androidx.core.view.ViewCompat;
 import androidx.lifecycle.ViewModelProviders;
 import androidx.navigation.Navigation;
 
 import org.thoughtcrime.securesms.R;
+import org.thoughtcrime.securesms.util.SpanUtil;
 
 public class CreateKbsPinFragment extends BaseKbsPinFragment<CreateKbsPinViewModel> {
 
@@ -47,6 +52,15 @@ public class CreateKbsPinFragment extends BaseKbsPinFragment<CreateKbsPinViewMod
     CreateKbsPinFragmentArgs args      = CreateKbsPinFragmentArgs.fromBundle(requireArguments());
 
     viewModel.getNavigationEvents().observe(getViewLifecycleOwner(), e -> onConfirmPin(e.getUserEntry(), e.getKeyboard(), args.getIsPinChange()));
+    viewModel.getErrorEvents().observe(getViewLifecycleOwner(), e -> {
+      if (e == CreateKbsPinViewModel.PinErrorEvent.WEAK_PIN) {
+        getLabel().setText(SpanUtil.color(ContextCompat.getColor(requireContext(), R.color.red),
+                                          getString(R.string.CreateKbsPinFragment__choose_a_stronger_pin)));
+        shake(getInput(), () -> getInput().getText().clear());
+      } else {
+        throw new AssertionError("Unexpected PIN error!");
+      }
+    });
     viewModel.getKeyboard().observe(getViewLifecycleOwner(), k -> {
       getLabel().setText(getLabelText(k));
       getInput().getText().clear();
@@ -76,4 +90,23 @@ public class CreateKbsPinFragment extends BaseKbsPinFragment<CreateKbsPinViewMod
   private String getPinLengthRestrictionText(@PluralsRes int plurals) {
     return requireContext().getResources().getQuantityString(plurals, KbsConstants.MINIMUM_PIN_LENGTH, KbsConstants.MINIMUM_PIN_LENGTH);
   }
+
+  private static void shake(@NonNull EditText view, @NonNull Runnable afterwards) {
+    TranslateAnimation shake = new TranslateAnimation(0, 30, 0, 0);
+    shake.setDuration(50);
+    shake.setRepeatCount(7);
+    shake.setAnimationListener(new Animation.AnimationListener() {
+      @Override
+      public void onAnimationStart(Animation animation) {}
+
+      @Override
+      public void onAnimationEnd(Animation animation) {
+        afterwards.run();
+      }
+
+      @Override
+      public void onAnimationRepeat(Animation animation) {}
+    });
+    view.startAnimation(shake);
+  }
 }

app/src/main/java/org/thoughtcrime/securesms/lock/v2/CreateKbsPinViewModel.java

@@ -2,18 +2,22 @@ package org.thoughtcrime.securesms.lock.v2;
 
 import androidx.annotation.MainThread;
 import androidx.annotation.NonNull;
+import androidx.annotation.StringRes;
 import androidx.core.util.Preconditions;
 import androidx.lifecycle.LiveData;
 import androidx.lifecycle.MutableLiveData;
 import androidx.lifecycle.ViewModel;
 
+import org.thoughtcrime.securesms.R;
 import org.thoughtcrime.securesms.util.SingleLiveEvent;
+import org.whispersystems.signalservice.internal.registrationpin.PinValidityChecker;
 
 public final class CreateKbsPinViewModel extends ViewModel implements BaseKbsPinViewModel {
 
   private final MutableLiveData<KbsPin>          userEntry = new MutableLiveData<>(KbsPin.EMPTY);
   private final MutableLiveData<PinKeyboardType> keyboard  = new MutableLiveData<>(PinKeyboardType.NUMERIC);
   private final SingleLiveEvent<NavigationEvent> events    = new SingleLiveEvent<>();
+  private final SingleLiveEvent<PinErrorEvent>   errors    = new SingleLiveEvent<>();
 
   @Override
   public LiveData<KbsPin> getUserEntry() {
@@ -27,6 +31,8 @@ public final class CreateKbsPinViewModel extends ViewModel implements BaseKbsPin
 
   LiveData<NavigationEvent> getNavigationEvents() { return events; }
 
+  LiveData<PinErrorEvent> getErrorEvents() { return errors; }
+
   @Override
   @MainThread
   public void setUserEntry(String userEntry) {
@@ -42,8 +48,14 @@ public final class CreateKbsPinViewModel extends ViewModel implements BaseKbsPin
   @Override
   @MainThread
   public void confirm() {
-    events.setValue(new NavigationEvent(Preconditions.checkNotNull(this.getUserEntry().getValue()),
-                                        Preconditions.checkNotNull(this.getKeyboard().getValue())));
+    KbsPin          pin      = Preconditions.checkNotNull(this.getUserEntry().getValue());
+    PinKeyboardType keyboard = Preconditions.checkNotNull(this.getKeyboard().getValue());
+
+    if (PinValidityChecker.valid(pin.toString())) {
+      events.setValue(new NavigationEvent(pin, keyboard));
+    } else {
+      errors.setValue(PinErrorEvent.WEAK_PIN);
+    }
   }
 
   static final class NavigationEvent {
@@ -63,4 +75,8 @@ public final class CreateKbsPinViewModel extends ViewModel implements BaseKbsPin
       return keyboard;
     }
   }
+
+  enum PinErrorEvent {
+    WEAK_PIN
+  }
 }