Create a WebsocketDrainedConstraint.

app/src/main/java/org/thoughtcrime/securesms/jobmanager/impl/WebsocketDrainedConstraint.java

@@ -0,0 +1,44 @@
+package org.thoughtcrime.securesms.jobmanager.impl;
+
+import android.app.job.JobInfo;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import org.thoughtcrime.securesms.dependencies.ApplicationDependencies;
+import org.thoughtcrime.securesms.jobmanager.Constraint;
+
+/**
+ * A constraint that is met once we have pulled down all messages from the websocket during initial
+ * load. See {@link org.thoughtcrime.securesms.messages.InitialMessageRetriever}.
+ */
+public final class WebsocketDrainedConstraint implements Constraint {
+
+  public static final String KEY = "WebsocketDrainedConstraint";
+
+  private WebsocketDrainedConstraint() {
+  }
+
+  @Override
+  public boolean isMet() {
+    return ApplicationDependencies.getInitialMessageRetriever().isCaughtUp();
+  }
+
+  @Override
+  public @NonNull String getFactoryKey() {
+    return KEY;
+  }
+
+  @RequiresApi(26)
+  @Override
+  public void applyToJobInfo(@NonNull JobInfo.Builder jobInfoBuilder) {
+  }
+
+  public static final class Factory implements Constraint.Factory<WebsocketDrainedConstraint> {
+
+    @Override
+    public WebsocketDrainedConstraint create() {
+      return new WebsocketDrainedConstraint();
+    }
+  }
+}

app/src/main/java/org/thoughtcrime/securesms/jobmanager/impl/WebsocketDrainedConstraintObserver.java

@@ -0,0 +1,22 @@
+package org.thoughtcrime.securesms.jobmanager.impl;
+
+import androidx.annotation.NonNull;
+
+import org.thoughtcrime.securesms.dependencies.ApplicationDependencies;
+import org.thoughtcrime.securesms.jobmanager.ConstraintObserver;
+
+/**
+ * An observer for {@link WebsocketDrainedConstraint}. Will fire when the
+ * {@link org.thoughtcrime.securesms.messages.InitialMessageRetriever} is caught up.
+ */
+public class WebsocketDrainedConstraintObserver implements ConstraintObserver {
+
+  private static final String REASON = WebsocketDrainedConstraintObserver.class.getSimpleName();
+
+  @Override
+  public void register(@NonNull Notifier notifier) {
+    ApplicationDependencies.getInitialMessageRetriever().addListener(() -> {
+      notifier.onConstraintMet(REASON);
+    });
+  }
+}