Implement ConnectivityStateMetrics sample

Test: ConnectivitySampleMetricsTest
Change-Id: I0afdda023208c3f8620cb5b89add66448af596d7
diff --git a/service/src/com/android/metrics/ConnectivitySampleMetricsHelper.java b/service/src/com/android/metrics/ConnectivitySampleMetricsHelper.java
new file mode 100644
index 0000000..93d1d5d
--- /dev/null
+++ b/service/src/com/android/metrics/ConnectivitySampleMetricsHelper.java
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.metrics;
+
+import android.annotation.NonNull;
+import android.app.StatsManager;
+import android.content.Context;
+import android.os.Handler;
+import android.util.Log;
+import android.util.StatsEvent;
+
+import com.android.modules.utils.HandlerExecutor;
+
+import java.util.List;
+import java.util.function.Supplier;
+
+/**
+ * A class to register, sample and send connectivity state metrics.
+ */
+public class ConnectivitySampleMetricsHelper implements StatsManager.StatsPullAtomCallback {
+    private static final String TAG = ConnectivitySampleMetricsHelper.class.getSimpleName();
+
+    final Supplier<StatsEvent> mDelegate;
+
+    /**
+     * Start collecting metrics.
+     * @param context some context to get services
+     * @param connectivityServiceHandler the connectivity service handler
+     * @param atomTag the tag to collect metrics from
+     * @param delegate a method returning data when called on the handler thread
+     */
+    // Unfortunately it seems essentially impossible to unit test this method. The only thing
+    // to test is that there is a call to setPullAtomCallback, but StatsManager is final and
+    // can't be mocked without mockito-extended. Using mockito-extended in FrameworksNetTests
+    // would have a very large impact on performance, while splitting the unit test for this
+    // class in a separate target would make testing very hard to manage. Therefore, there
+    // can unfortunately be no unit tests for this method, but at least it is very simple.
+    public static void start(@NonNull final Context context,
+            @NonNull final Handler connectivityServiceHandler,
+            final int atomTag,
+            @NonNull final Supplier<StatsEvent> delegate) {
+        final ConnectivitySampleMetricsHelper metrics =
+                new ConnectivitySampleMetricsHelper(delegate);
+        final StatsManager mgr = context.getSystemService(StatsManager.class);
+        if (null == mgr) return; // No metrics for you
+        mgr.setPullAtomCallback(atomTag, null /* metadata */,
+                new HandlerExecutor(connectivityServiceHandler), metrics);
+    }
+
+    public ConnectivitySampleMetricsHelper(@NonNull final Supplier<StatsEvent> delegate) {
+        mDelegate = delegate;
+    }
+
+    @Override
+    public int onPullAtom(final int atomTag, final List<StatsEvent> data) {
+        Log.d(TAG, "Sampling data for atom : " + atomTag);
+        data.add(mDelegate.get());
+        return StatsManager.PULL_SUCCESS;
+    }
+}