Add a charging constraint to the backup job.

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

@@ -0,0 +1,43 @@
+package org.thoughtcrime.securesms.jobmanager.impl;
+
+import android.app.job.JobInfo;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import org.thoughtcrime.securesms.jobmanager.Constraint;
+
+/**
+ * Job constraint for determining whether or not the device is actively charging.
+ */
+public class ChargingConstraint implements Constraint {
+
+  public static final String KEY = "ChargingConstraint";
+
+  private ChargingConstraint() {
+  }
+
+  @Override
+  public boolean isMet() {
+    return ChargingConstraintObserver.isCharging();
+  }
+
+  @Override
+  public @NonNull String getFactoryKey() {
+    return KEY;
+  }
+
+  @RequiresApi(26)
+  @Override
+  public void applyToJobInfo(@NonNull JobInfo.Builder jobInfoBuilder) {
+    jobInfoBuilder.setRequiresCharging(true);
+  }
+
+  public static final class Factory implements Constraint.Factory<ChargingConstraint> {
+
+    @Override
+    public ChargingConstraint create() {
+      return new ChargingConstraint();
+    }
+  }
+}

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

@@ -0,0 +1,62 @@
+package org.thoughtcrime.securesms.jobmanager.impl;
+
+import android.app.Application;
+import android.content.BroadcastReceiver;
+import android.content.Context;
+import android.content.Intent;
+import android.content.IntentFilter;
+import android.os.BatteryManager;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.annotation.RequiresApi;
+
+import org.thoughtcrime.securesms.jobmanager.ConstraintObserver;
+
+/**
+ * Observes the charging state of the device and notifies the JobManager system when appropriate.
+ */
+public class ChargingConstraintObserver implements ConstraintObserver {
+
+  private static final String REASON         = ChargingConstraintObserver.class.getSimpleName();
+  private static final int    STATUS_BATTERY = 0;
+
+  private final Application application;
+
+  private static volatile boolean charging;
+
+  public ChargingConstraintObserver(@NonNull Application application) {
+    this.application = application;
+  }
+
+  @Override
+  public void register(@NonNull Notifier notifier) {
+    Intent intent = application.registerReceiver(new BroadcastReceiver() {
+      @Override
+      public void onReceive(Context context, Intent intent) {
+        boolean wasCharging = charging;
+
+        charging = isCharging(intent);
+
+        if (charging && !wasCharging) {
+          notifier.onConstraintMet(REASON);
+        }
+      }
+    }, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
+
+    charging = isCharging(intent);
+  }
+
+  public static boolean isCharging() {
+    return charging;
+  }
+
+  private static boolean isCharging(@Nullable Intent intent) {
+    if (intent == null) {
+      return false;
+    }
+
+    int status = intent.getIntExtra(BatteryManager.EXTRA_PLUGGED, STATUS_BATTERY);
+    return status != STATUS_BATTERY;
+  }
+}