android: added TrainingJob which will run training jobs in the backgr…

…ound for the model

android/library/src/main/java/ai/luk/TrainingJob.java

@@ -0,0 +1,88 @@
+package ai.luk;
+
+import android.app.job.JobInfo;
+import android.app.job.JobScheduler;
+import android.app.job.JobService;
+import android.app.job.JobParameters;
+import android.content.Context;
+import android.content.ComponentName;
+
+import ai.luk.ModelType;
+
+/*
+To use this training job you'll need to extend it and implement the domain,
+modelType and dataDir methods. Your code needs to call the schedule() method at
+least once.
+You'll also need to define the service in your AndroidManifest.xml file.
+
+<service
+android:name=".yourpackage.TrainingJob"
+android:permission="android.permission.BIND_JOB_SERVICE"
+android:permission="android.permission.RECEIVE_BOOT_COMPLETED"
+android:exported="true"/>
+
+*/
+public abstract class TrainingJob extends JobService {
+  private ModelType mt;
+
+  public void schedule() {
+    JobScheduler jobScheduler =
+      (JobScheduler) getSystemService(Context.JOB_SCHEDULER_SERVICE);
+    int id = jobId();
+
+    // Check if the job is already scheduled and reschedule it in case the job
+    // has changed.
+    for (JobInfo ji : jobScheduler.getAllPendingJobs()) {
+      if (ji.getId() == id) {
+        jobScheduler.cancel(id);
+      }
+    }
+
+    jobScheduler.schedule(new JobInfo.Builder(id,
+          new ComponentName(this, this.getClass()))
+        .setRequiredNetworkType(JobInfo.NETWORK_TYPE_UNMETERED)
+        .setPersisted(true)
+        .setRequiresCharging(true)
+        .setRequiresDeviceIdle(true)
+        .setPeriodic(intervalMillis())
+        .build());
+  }
+
+  @Override
+  public boolean onStartJob(final JobParameters params) {
+    try {
+      mt = new ModelType(domain(), modelType(), dataDir());
+      mt.startTraining();
+    } catch (Exception e) {
+      throw new RuntimeException(e);
+    }
+    return true;
+  }
+
+  @Override
+  public boolean onStopJob(final JobParameters params) {
+    if (mt != null) {
+      try {
+        mt.stopTraining();
+      } catch (Exception e) {
+        throw new RuntimeException(e);
+      }
+    }
+    return true;
+  }
+
+  public int jobId() {
+    return ("training:"+domain()+"/"+modelType()+"/"+dataDir()).hashCode();
+  }
+
+  // intervalMillis is the number of milliseconds that the training job will run
+  // at most once per.
+  public long intervalMillis() {
+    // default to 6 hours.
+    return 6 * 60 * 60 * 1000;
+  }
+
+  public abstract String domain();
+  public abstract String modelType();
+  public abstract String dataDir();
+}