Add BatteryHistoricalLogUtil class

- Impl optimize mode log mechanism to record optimize setup flow
 - Log optimize action with MANUAL, APPLY, RESET and RESTORE
 - Use proto file to serialize logs
 sample result: https://screenshot.googleplex.com/5KPrHVGb4pMvS7V.png

Bug: 241735485
Test: make SettingsRoboTests
Change-Id: I879663de4cf45d0cfb9cd7eee957eeb65addfbe1

src/com/android/settings/fuelgauge/BatteryHistoricalLogUtil.java

@@ -0,0 +1,129 @@
+/*
+ * 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.fuelgauge;
+
+import android.content.Context;
+import android.content.SharedPreferences;
+import android.util.Base64;
+import android.util.Log;
+
+import com.android.settings.fuelgauge.BatteryOptimizeHistoricalLogEntry.Action;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.protobuf.InvalidProtocolBufferException;
+import com.google.protobuf.MessageLite;
+
+import java.io.PrintWriter;
+import java.util.List;
+
+/** Writes and reads a historical log of battery related state change events. */
+public final class BatteryHistoricalLogUtil {
+    private static final String BATTERY_OPTIMIZE_FILE_NAME = "battery_optimize_historical_logs";
+    private static final String LOGS_KEY = "battery_optimize_logs_key";
+    private static final String TAG = "BatteryHistoricalLogUtil";
+
+    @VisibleForTesting
+    static final int MAX_ENTRIES = 40;
+
+    /**
+     * Writes a log entry.
+     *
+     * <p>Keeps up to {@link #MAX_ENTRIES} in the log, once that number is exceeded, it prunes the
+     * oldest one.
+     */
+    static void writeLog(Context context, Action action, String pkg, String actionDescription) {
+        writeLog(
+                context,
+                BatteryOptimizeHistoricalLogEntry.newBuilder()
+                        .setPackageName(pkg)
+                        .setAction(action)
+                        .setActionDescription(actionDescription)
+                        .build());
+    }
+
+    private static void writeLog(Context context, BatteryOptimizeHistoricalLogEntry logEntry) {
+        SharedPreferences sharedPreferences = getSharedPreferences(context);
+
+        BatteryOptimizeHistoricalLog existingLog =
+                parseLogFromString(sharedPreferences.getString(LOGS_KEY, ""));
+        BatteryOptimizeHistoricalLog.Builder newLogBuilder = existingLog.toBuilder();
+        // Prune old entries
+        if (existingLog.getLogEntryCount() >= MAX_ENTRIES) {
+            newLogBuilder.removeLogEntry(0);
+        }
+        newLogBuilder.addLogEntry(logEntry);
+
+        sharedPreferences
+                .edit()
+                .putString(
+                        LOGS_KEY,
+                        Base64.encodeToString(newLogBuilder.build().toByteArray(), Base64.DEFAULT))
+                .apply();
+    }
+
+    private static BatteryOptimizeHistoricalLog parseLogFromString(String storedLogs) {
+        return parseProtoFromString(storedLogs, BatteryOptimizeHistoricalLog.getDefaultInstance());
+    }
+
+    @SuppressWarnings("unchecked")
+    private static <T extends MessageLite> T parseProtoFromString(
+            String serializedProto, T protoClass) {
+        if (serializedProto.isEmpty()) {
+            return (T) protoClass.getDefaultInstanceForType();
+        }
+        try {
+            return (T) protoClass.getParserForType()
+                    .parseFrom(Base64.decode(serializedProto, Base64.DEFAULT));
+        } catch (InvalidProtocolBufferException e) {
+            Log.e(TAG, "Failed to deserialize proto class", e);
+            return (T) protoClass.getDefaultInstanceForType();
+        }
+    }
+
+    /**
+     * Prints the historical log that has previously been stored by this utility.
+     */
+    public static void printBatteryOptimizeHistoricalLog(Context context, PrintWriter writer) {
+        writer.println("Battery optimize state history:");
+        SharedPreferences sharedPreferences = getSharedPreferences(context);
+        BatteryOptimizeHistoricalLog existingLog =
+                parseLogFromString(sharedPreferences.getString(LOGS_KEY, ""));
+        List<BatteryOptimizeHistoricalLogEntry> logEntryList = existingLog.getLogEntryList();
+        if (logEntryList.isEmpty()) {
+            writer.println("\tNo past logs.");
+        } else {
+            logEntryList.forEach(entry -> writer.println(toString(entry)));
+        }
+    }
+
+    /**
+     * Gets the unique key for logging, combined with package name, delimiter and user id.
+     */
+    static String getPackageNameWithUserId(String pkgName, int userId) {
+        return pkgName + ":" + userId;
+    }
+
+    private static String toString(BatteryOptimizeHistoricalLogEntry entry) {
+        return String.format("%s\tAction:%s\tEvent:%s",
+                entry.getPackageName(), entry.getAction(), entry.getActionDescription());
+    }
+
+    @VisibleForTesting
+    static SharedPreferences getSharedPreferences(Context context) {
+        return context.getSharedPreferences(BATTERY_OPTIMIZE_FILE_NAME, Context.MODE_PRIVATE);
+    }
+}