[Catalyst] Migrate "Use Data Saver" settings

Bug: 368359883
Flag: com.android.settings.flags.catalyst
Test: manual
Change-Id: I2ee30cdd5edbfb13b5bf67e4c3b93b787c52a767

src/com/android/settings/datausage/DataSaverMainSwitchPreference.kt

@@ -0,0 +1,71 @@
+/*
+ * Copyright (C) 2024 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.datausage
+
+import android.content.Context
+import com.android.settings.R
+import com.android.settings.widget.MainSwitchBarMetadata
+import com.android.settingslib.datastore.KeyValueStore
+import com.android.settingslib.datastore.NoOpKeyedObservable
+import com.android.settingslib.metadata.PreferenceLifecycleContext
+import com.android.settingslib.metadata.PreferenceLifecycleProvider
+import com.android.settingslib.metadata.ReadWritePermit
+
+class DataSaverMainSwitchPreference(context: Context) :
+    MainSwitchBarMetadata, PreferenceLifecycleProvider {
+
+    private val dataSaverBackend = DataSaverBackend(context)
+    private var dataSaverBackendListener: DataSaverBackend.Listener? = null
+
+    override val key
+        get() = "use_data_saver"
+
+    override val title
+        get() = R.string.data_saver_switch_title
+
+    override fun storage(context: Context): KeyValueStore = DataSaverStore(dataSaverBackend)
+
+    override fun getWritePermit(context: Context, value: Boolean?, myUid: Int, callingUid: Int) =
+        ReadWritePermit.ALLOW
+
+    override fun onStart(context: PreferenceLifecycleContext) {
+        val listener = DataSaverBackend.Listener { context.notifyPreferenceChange(this) }
+        dataSaverBackendListener = listener
+        dataSaverBackend.addListener(listener)
+    }
+
+    override fun onStop(context: PreferenceLifecycleContext) {
+        dataSaverBackendListener?.let {
+            dataSaverBackend.remListener(it)
+            dataSaverBackendListener = null
+        }
+    }
+
+    @Suppress("UNCHECKED_CAST")
+    private class DataSaverStore(private val dataSaverBackend: DataSaverBackend) :
+        NoOpKeyedObservable<String>(), KeyValueStore {
+
+        override fun contains(key: String) = true // just assume the datastore contains the value
+
+        override fun <T : Any> getValue(key: String, valueType: Class<T>): T? =
+            dataSaverBackend.isDataSaverEnabled as T?
+
+        override fun <T : Any> setValue(key: String, valueType: Class<T>, value: T?) {
+            dataSaverBackend.isDataSaverEnabled = value as Boolean
+        }
+    }
+}