/*
 * Copyright (C) 2016 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 android.os.health;

import android.content.Context;
import android.os.BatteryStats;
import android.os.Process;
import android.os.RemoteException;
import android.os.ServiceManager;

import com.android.internal.app.IBatteryStats;

/**
 * Provides access to data about how various system resources are used by applications.
 * @more
 * <p>
 * If you are going to be using this class to log your application's resource usage,
 * please consider the amount of resources (battery, network, etc) that will be used
 * by the logging itself.  It can be substantial.
 * <p>
 * <b>Battery Usage</b><br>
 * The statistics related to power (battery) usage are recorded since the device
 * was last unplugged. It is expected that applications schedule more work to do
 * while the device is plugged in (e.g. using {@link android.app.job.JobScheduler
 * JobScheduler}), and while that can affect charging rates, it is still preferable
 * to actually draining the battery.
 */
public class SystemHealthManager {
    private final IBatteryStats mBatteryStats;

    /**
     * Construct a new SystemHealthManager object.
     * @hide
     */
    public SystemHealthManager() {
        mBatteryStats = IBatteryStats.Stub.asInterface(
            ServiceManager.getService(BatteryStats.SERVICE_NAME));
    }

    /**
     * Obtain a SystemHealthManager object for the supplied context.
     *
     * @hide
     */
    public static SystemHealthManager from(Context context) {
        return (SystemHealthManager)context.getSystemService(Context.SYSTEM_HEALTH_SERVICE);
    }

    /**
     * Return a {@link HealthStats} object containing a snapshot of system health
     * metrics for the given uid (user-id, which in usually corresponds to application).
     * @more
     *
     * An application must hold the {@link android.Manifest.permission#BATTERY_STATS
     * android.permission.BATTERY_STATS} permission in order to retrieve any HealthStats
     * other than its own.
     *
     * @param uid User ID for a given application.
     * @return A {@link HealthStats} object containing the metrics for the requested
     * application. The keys for this HealthStats object will be from the {@link UidHealthStats}
     * class.
     * @see Process#myUid() Process.myUid()
     */
    public HealthStats takeUidSnapshot(int uid) {
        try {
            final HealthStatsParceler parceler = mBatteryStats.takeUidSnapshot(uid);
            return parceler.getHealthStats();
        } catch (RemoteException ex) {
            throw new RuntimeException(ex);
        }
    }

    /**
     * Return a {@link HealthStats} object containing a snapshot of system health
     * metrics for the application calling this API. This method is the same as calling
     * {@code takeUidSnapshot(Process.myUid())}.
     *
     * @return A {@link HealthStats} object containing the metrics for this application. The keys
     * for this HealthStats object will be from the {@link UidHealthStats} class.
     */
    public HealthStats takeMyUidSnapshot() {
        return takeUidSnapshot(Process.myUid());
    }

    /**
     * Return a {@link HealthStats} object containing a snapshot of system health
     * metrics for the given uids (user-id, which in usually corresponds to application).
     * @more
     *
     * An application must hold the {@link android.Manifest.permission#BATTERY_STATS
     * android.permission.BATTERY_STATS} permission in order to retrieve any HealthStats
     * other than its own.
     *
     * @param uids An array of User IDs to retrieve.
     * @return An array of {@link HealthStats} objects containing the metrics for each of
     * the requested uids. The keys for this HealthStats object will be from the
     * {@link UidHealthStats} class.
     */
    public HealthStats[] takeUidSnapshots(int[] uids) {
        try {
            final HealthStatsParceler[] parcelers = mBatteryStats.takeUidSnapshots(uids);
            final HealthStats[] results = new HealthStats[uids.length];
            final int N = uids.length;
            for (int i=0; i<N; i++) {
                results[i] = parcelers[i].getHealthStats();
            }
            return results;
        } catch (RemoteException ex) {
            throw new RuntimeException(ex);
        }
    }

}