[Settings] Code refactor for monitoring service state

This is for monitoring the status of service state when Lifecycle state
STARTED or RESUMED.

Bug: 229689535
Test: unit test
Change-Id: If6bac5c04caae67d6293c5a69e3130789e9e588e

src/com/android/settings/network/helper/ServiceStateStatus.java

@@ -0,0 +1,104 @@
+/*
+ * Copyright (C) 2022 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.settings.network.helper;
+
+import android.telephony.ServiceState;
+import android.telephony.TelephonyCallback;
+import android.telephony.TelephonyManager;
+import android.util.Log;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.VisibleForTesting;
+import androidx.lifecycle.Lifecycle;
+import androidx.lifecycle.LiveData;
+
+import java.util.concurrent.Executor;
+import java.util.function.Consumer;
+
+/**
+ * A {@link LiveData} as a mapping of allowed network types reported from {@link TelephonyCallback}.
+ * Only got update when Lifecycle.State is considered as STARTED or RESUMED.
+ *
+ * {@code null} when status unknown. Other values are {@link ServiceState}.
+ */
+@VisibleForTesting
+public class ServiceStateStatus extends LiveData<ServiceState> {
+    private static final String TAG = "ServiceStateStatus";
+
+    @VisibleForTesting
+    protected ServiceStateProducer mServiceStateProducer;
+
+    @VisibleForTesting
+    protected LifecycleCallbackTelephonyAdapter mAdapter;
+
+    @VisibleForTesting
+    protected Consumer<ServiceState> mLiveDataUpdater = status -> setValue(status);
+
+    /**
+     * Constructor
+     * @param lifecycle {@link Lifecycle} to monitor
+     * @param telephonyManager {@link TelephonyManager} to interact with
+     * @param executor {@link Executor} for receiving the notify from telephony framework.
+     */
+    @VisibleForTesting
+    public ServiceStateStatus(@NonNull Lifecycle lifecycle,
+            @NonNull TelephonyManager telephonyManager, Executor executor) {
+        super();
+
+        mServiceStateProducer = new ServiceStateProducer(this);
+
+        mAdapter = new LifecycleCallbackTelephonyAdapter<ServiceState>(lifecycle,
+                telephonyManager, mServiceStateProducer, executor, mLiveDataUpdater) {
+            @Override
+            public void setCallbackActive(boolean isActive) {
+                super.setCallbackActive(isActive);
+                if (!isActive) {
+                    /**
+                     * Set to unknown status when no longer actively monitoring
+                     * {@link TelephonyCallback}.
+                     */
+                    mLiveDataUpdater.accept(null);
+                }
+            }
+        };
+    }
+
+    /**
+     * An implementation of TelephonyCallback.
+     *
+     * Change of allowed network type will be forward to
+     * {@link LifecycleCallbackTelephonyAdapter}.
+     */
+    @VisibleForTesting
+    protected static class ServiceStateProducer extends TelephonyCallback
+            implements TelephonyCallback.ServiceStateListener {
+        private final ServiceStateStatus mStatus;
+
+        /**
+         * Constructor
+         * @param status {@link ServiceStateStatus}
+         */
+        public ServiceStateProducer(ServiceStateStatus status) {
+            mStatus = status;
+        }
+
+        @Override
+        public void onServiceStateChanged(ServiceState serviceState) {
+            mStatus.mAdapter.postResult(serviceState);
+        }
+    }
+}