/*
 * Copyright 2017 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.app;

import static android.Manifest.permission.DUMP;
import static android.Manifest.permission.PACKAGE_USAGE_STATS;

import android.annotation.CallbackExecutor;
import android.annotation.NonNull;
import android.annotation.Nullable;
import android.annotation.RequiresPermission;
import android.annotation.SystemApi;
import android.content.Context;
import android.os.Binder;
import android.os.IPullAtomCallback;
import android.os.IPullAtomResultReceiver;
import android.os.IStatsManagerService;
import android.os.IStatsd;
import android.os.RemoteException;
import android.os.StatsFrameworkInitializer;
import android.util.AndroidException;
import android.util.Log;
import android.util.StatsEvent;
import android.util.StatsEventParcel;

import com.android.internal.annotations.GuardedBy;
import com.android.internal.annotations.VisibleForTesting;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Executor;

/**
 * API for statsd clients to send configurations and retrieve data.
 *
 * @hide
 */
@SystemApi
public final class StatsManager {
    private static final String TAG = "StatsManager";
    private static final boolean DEBUG = false;

    private static final Object sLock = new Object();
    private final Context mContext;

    @GuardedBy("sLock")
    private IStatsd mService;

    @GuardedBy("sLock")
    private IStatsManagerService mStatsManagerService;

    /**
     * Long extra of uid that added the relevant stats config.
     */
    public static final String EXTRA_STATS_CONFIG_UID = "android.app.extra.STATS_CONFIG_UID";
    /**
     * Long extra of the relevant stats config's configKey.
     */
    public static final String EXTRA_STATS_CONFIG_KEY = "android.app.extra.STATS_CONFIG_KEY";
    /**
     * Long extra of the relevant statsd_config.proto's Subscription.id.
     */
    public static final String EXTRA_STATS_SUBSCRIPTION_ID =
            "android.app.extra.STATS_SUBSCRIPTION_ID";
    /**
     * Long extra of the relevant statsd_config.proto's Subscription.rule_id.
     */
    public static final String EXTRA_STATS_SUBSCRIPTION_RULE_ID =
            "android.app.extra.STATS_SUBSCRIPTION_RULE_ID";
    /**
     *   List<String> of the relevant statsd_config.proto's BroadcastSubscriberDetails.cookie.
     *   Obtain using {@link android.content.Intent#getStringArrayListExtra(String)}.
     */
    public static final String EXTRA_STATS_BROADCAST_SUBSCRIBER_COOKIES =
            "android.app.extra.STATS_BROADCAST_SUBSCRIBER_COOKIES";
    /**
     * Extra of a {@link android.os.StatsDimensionsValue} representing sliced dimension value
     * information.
     */
    public static final String EXTRA_STATS_DIMENSIONS_VALUE =
            "android.app.extra.STATS_DIMENSIONS_VALUE";
    /**
     * Long array extra of the active configs for the uid that added those configs.
     */
    public static final String EXTRA_STATS_ACTIVE_CONFIG_KEYS =
            "android.app.extra.STATS_ACTIVE_CONFIG_KEYS";

    /**
     * Broadcast Action: Statsd has started.
     * Configurations and PendingIntents can now be sent to it.
     */
    public static final String ACTION_STATSD_STARTED = "android.app.action.STATSD_STARTED";

    // Pull atom callback return codes.
    /**
     * Value indicating that this pull was successful and that the result should be used.
     *
     **/
    public static final int PULL_SUCCESS = 0;

    /**
     * Value indicating that this pull was unsuccessful and that the result should not be used.
     **/
    public static final int PULL_SKIP = 1;

    /**
     * @hide
     **/
    @VisibleForTesting public static final long DEFAULT_COOL_DOWN_MILLIS = 1_000L; // 1 second.

    /**
     * @hide
     **/
    @VisibleForTesting public static final long DEFAULT_TIMEOUT_MILLIS = 10_000L; // 10 seconds.

    /**
     * Constructor for StatsManagerClient.
     *
     * @hide
     */
    public StatsManager(Context context) {
        mContext = context;
    }

    /**
     * Adds the given configuration and associates it with the given configKey. If a config with the
     * given configKey already exists for the caller's uid, it is replaced with the new one.
     *
     * @param configKey An arbitrary integer that allows clients to track the configuration.
     * @param config    Wire-encoded StatsdConfig proto that specifies metrics (and all
     *                  dependencies eg, conditions and matchers).
     * @throws StatsUnavailableException if unsuccessful due to failing to connect to stats service
     * @throws IllegalArgumentException if config is not a wire-encoded StatsdConfig proto
     */
    @RequiresPermission(allOf = { DUMP, PACKAGE_USAGE_STATS })
    public void addConfig(long configKey, byte[] config) throws StatsUnavailableException {
        synchronized (sLock) {
            try {
                IStatsManagerService service = getIStatsManagerServiceLocked();
                // can throw IllegalArgumentException
                service.addConfiguration(configKey, config, mContext.getOpPackageName());
            } catch (RemoteException e) {
                Log.e(TAG, "Failed to connect to statsmanager when adding configuration");
                throw new StatsUnavailableException("could not connect", e);
            } catch (SecurityException e) {
                throw new StatsUnavailableException(e.getMessage(), e);
            } catch (IllegalStateException e) {
                Log.e(TAG, "Failed to addConfig in statsmanager");
                throw new StatsUnavailableException(e.getMessage(), e);
            }
        }
    }

    // TODO: Temporary for backwards compatibility. Remove.
    /**
     * @deprecated Use {@link #addConfig(long, byte[])}
     */
    @Deprecated
    @RequiresPermission(allOf = { DUMP, PACKAGE_USAGE_STATS })
    public boolean addConfiguration(long configKey, byte[] config) {
        try {
            addConfig(configKey, config);
            return true;
        } catch (StatsUnavailableException | IllegalArgumentException e) {
            return false;
        }
    }

    /**
     * Remove a configuration from logging.
     *
     * @param configKey Configuration key to remove.
     * @throws StatsUnavailableException if unsuccessful due to failing to connect to stats service
     */
    @RequiresPermission(allOf = { DUMP, PACKAGE_USAGE_STATS })
    public void removeConfig(long configKey) throws StatsUnavailableException {
        synchronized (sLock) {
            try {
                IStatsManagerService service = getIStatsManagerServiceLocked();
                service.removeConfiguration(configKey, mContext.getOpPackageName());
            } catch (RemoteException e) {
                Log.e(TAG, "Failed to connect to statsmanager when removing configuration");
                throw new StatsUnavailableException("could not connect", e);
            } catch (SecurityException e) {
                throw new StatsUnavailableException(e.getMessage(), e);
            } catch (IllegalStateException e) {
                Log.e(TAG, "Failed to removeConfig in statsmanager");
                throw new StatsUnavailableException(e.getMessage(), e);
            }
        }
    }

    // TODO: Temporary for backwards compatibility. Remove.
    /**
     * @deprecated Use {@link #removeConfig(long)}
     */
    @Deprecated
    @RequiresPermission(allOf = { DUMP, PACKAGE_USAGE_STATS })
    public boolean removeConfiguration(long configKey) {
        try {
            removeConfig(configKey);
            return true;
        } catch (StatsUnavailableException e) {
            return false;
        }
    }

    /**
     * Set the PendingIntent to be used when broadcasting subscriber information to the given
     * subscriberId within the given config.
     * <p>
     * Suppose that the calling uid has added a config with key configKey, and that in this config
     * it is specified that when a particular anomaly is detected, a broadcast should be sent to
     * a BroadcastSubscriber with id subscriberId. This function links the given pendingIntent with
     * that subscriberId (for that config), so that this pendingIntent is used to send the broadcast
     * when the anomaly is detected.
     * <p>
     * When statsd sends the broadcast, the PendingIntent will used to send an intent with
     * information of
     * {@link #EXTRA_STATS_CONFIG_UID},
     * {@link #EXTRA_STATS_CONFIG_KEY},
     * {@link #EXTRA_STATS_SUBSCRIPTION_ID},
     * {@link #EXTRA_STATS_SUBSCRIPTION_RULE_ID},
     * {@link #EXTRA_STATS_BROADCAST_SUBSCRIBER_COOKIES}, and
     * {@link #EXTRA_STATS_DIMENSIONS_VALUE}.
     * <p>
     * This function can only be called by the owner (uid) of the config. It must be called each
     * time statsd starts. The config must have been added first (via {@link #addConfig}).
     *
     * @param pendingIntent the PendingIntent to use when broadcasting info to the subscriber
     *                      associated with the given subscriberId. May be null, in which case
     *                      it undoes any previous setting of this subscriberId.
     * @param configKey     The integer naming the config to which this subscriber is attached.
     * @param subscriberId  ID of the subscriber, as used in the config.
     * @throws StatsUnavailableException if unsuccessful due to failing to connect to stats service
     */
    @RequiresPermission(allOf = { DUMP, PACKAGE_USAGE_STATS })
    public void setBroadcastSubscriber(
            PendingIntent pendingIntent, long configKey, long subscriberId)
            throws StatsUnavailableException {
        synchronized (sLock) {
            try {
                IStatsManagerService service = getIStatsManagerServiceLocked();
                if (pendingIntent != null) {
                    service.setBroadcastSubscriber(configKey, subscriberId, pendingIntent,
                            mContext.getOpPackageName());
                } else {
                    service.unsetBroadcastSubscriber(configKey, subscriberId,
                            mContext.getOpPackageName());
                }
            } catch (RemoteException e) {
                Log.e(TAG, "Failed to connect to statsmanager when adding broadcast subscriber",
                        e);
                throw new StatsUnavailableException("could not connect", e);
            } catch (SecurityException e) {
                throw new StatsUnavailableException(e.getMessage(), e);
            }
        }
    }

    // TODO: Temporary for backwards compatibility. Remove.
    /**
     * @deprecated Use {@link #setBroadcastSubscriber(PendingIntent, long, long)}
     */
    @Deprecated
    @RequiresPermission(allOf = { DUMP, PACKAGE_USAGE_STATS })
    public boolean setBroadcastSubscriber(
            long configKey, long subscriberId, PendingIntent pendingIntent) {
        try {
            setBroadcastSubscriber(pendingIntent, configKey, subscriberId);
            return true;
        } catch (StatsUnavailableException e) {
            return false;
        }
    }

    /**
     * Registers the operation that is called to retrieve the metrics data. This must be called
     * each time statsd starts. The config must have been added first (via {@link #addConfig},
     * although addConfig could have been called on a previous boot). This operation allows
     * statsd to send metrics data whenever statsd determines that the metrics in memory are
     * approaching the memory limits. The fetch operation should call {@link #getReports} to fetch
     * the data, which also deletes the retrieved metrics from statsd's memory.
     *
     * @param pendingIntent the PendingIntent to use when broadcasting info to the subscriber
     *                      associated with the given subscriberId. May be null, in which case
     *                      it removes any associated pending intent with this configKey.
     * @param configKey     The integer naming the config to which this operation is attached.
     * @throws StatsUnavailableException if unsuccessful due to failing to connect to stats service
     */
    @RequiresPermission(allOf = { DUMP, PACKAGE_USAGE_STATS })
    public void setFetchReportsOperation(PendingIntent pendingIntent, long configKey)
            throws StatsUnavailableException {
        synchronized (sLock) {
            try {
                IStatsManagerService service = getIStatsManagerServiceLocked();
                if (pendingIntent == null) {
                    service.removeDataFetchOperation(configKey, mContext.getOpPackageName());
                } else {
                    service.setDataFetchOperation(configKey, pendingIntent,
                            mContext.getOpPackageName());
                }

            } catch (RemoteException e) {
                Log.e(TAG, "Failed to connect to statsmanager when registering data listener.");
                throw new StatsUnavailableException("could not connect", e);
            } catch (SecurityException e) {
                throw new StatsUnavailableException(e.getMessage(), e);
            }
        }
    }

    /**
     * Registers the operation that is called whenever there is a change in which configs are
     * active. This must be called each time statsd starts. This operation allows
     * statsd to inform clients that they should pull data of the configs that are currently
     * active. The activeConfigsChangedOperation should set periodic alarms to pull data of configs
     * that are active and stop pulling data of configs that are no longer active.
     *
     * @param pendingIntent the PendingIntent to use when broadcasting info to the subscriber
     *                      associated with the given subscriberId. May be null, in which case
     *                      it removes any associated pending intent for this client.
     * @return A list of configs that are currently active for this client. If the pendingIntent is
     *         null, this will be an empty list.
     * @throws StatsUnavailableException if unsuccessful due to failing to connect to stats service
     */
    @RequiresPermission(allOf = { DUMP, PACKAGE_USAGE_STATS })
    public @NonNull long[] setActiveConfigsChangedOperation(@Nullable PendingIntent pendingIntent)
            throws StatsUnavailableException {
        synchronized (sLock) {
            try {
                IStatsManagerService service = getIStatsManagerServiceLocked();
                if (pendingIntent == null) {
                    service.removeActiveConfigsChangedOperation(mContext.getOpPackageName());
                    return new long[0];
                } else {
                    return service.setActiveConfigsChangedOperation(pendingIntent,
                            mContext.getOpPackageName());
                }

            } catch (RemoteException e) {
                Log.e(TAG, "Failed to connect to statsmanager "
                        + "when registering active configs listener.");
                throw new StatsUnavailableException("could not connect", e);
            } catch (SecurityException e) {
                throw new StatsUnavailableException(e.getMessage(), e);
            }
        }
    }

    // TODO: Temporary for backwards compatibility. Remove.
    /**
     * @deprecated Use {@link #setFetchReportsOperation(PendingIntent, long)}
     */
    @Deprecated
    @RequiresPermission(allOf = { DUMP, PACKAGE_USAGE_STATS })
    public boolean setDataFetchOperation(long configKey, PendingIntent pendingIntent) {
        try {
            setFetchReportsOperation(pendingIntent, configKey);
            return true;
        } catch (StatsUnavailableException e) {
            return false;
        }
    }

    /**
     * Request the data collected for the given configKey.
     * This getter is destructive - it also clears the retrieved metrics from statsd's memory.
     *
     * @param configKey Configuration key to retrieve data from.
     * @return Serialized ConfigMetricsReportList proto.
     * @throws StatsUnavailableException if unsuccessful due to failing to connect to stats service
     */
    @RequiresPermission(allOf = { DUMP, PACKAGE_USAGE_STATS })
    public byte[] getReports(long configKey) throws StatsUnavailableException {
        synchronized (sLock) {
            try {
                IStatsManagerService service = getIStatsManagerServiceLocked();
                return service.getData(configKey, mContext.getOpPackageName());
            } catch (RemoteException e) {
                Log.e(TAG, "Failed to connect to statsmanager when getting data");
                throw new StatsUnavailableException("could not connect", e);
            } catch (SecurityException e) {
                throw new StatsUnavailableException(e.getMessage(), e);
            } catch (IllegalStateException e) {
                Log.e(TAG, "Failed to getReports in statsmanager");
                throw new StatsUnavailableException(e.getMessage(), e);
            }
        }
    }

    // TODO: Temporary for backwards compatibility. Remove.
    /**
     * @deprecated Use {@link #getReports(long)}
     */
    @Deprecated
    @RequiresPermission(allOf = { DUMP, PACKAGE_USAGE_STATS })
    public @Nullable byte[] getData(long configKey) {
        try {
            return getReports(configKey);
        } catch (StatsUnavailableException e) {
            return null;
        }
    }

    /**
     * Clients can request metadata for statsd. Will contain stats across all configurations but not
     * the actual metrics themselves (metrics must be collected via {@link #getReports(long)}.
     * This getter is not destructive and will not reset any metrics/counters.
     *
     * @return Serialized StatsdStatsReport proto.
     * @throws StatsUnavailableException if unsuccessful due to failing to connect to stats service
     */
    @RequiresPermission(allOf = { DUMP, PACKAGE_USAGE_STATS })
    public byte[] getStatsMetadata() throws StatsUnavailableException {
        synchronized (sLock) {
            try {
                IStatsManagerService service = getIStatsManagerServiceLocked();
                return service.getMetadata(mContext.getOpPackageName());
            } catch (RemoteException e) {
                Log.e(TAG, "Failed to connect to statsmanager when getting metadata");
                throw new StatsUnavailableException("could not connect", e);
            } catch (SecurityException e) {
                throw new StatsUnavailableException(e.getMessage(), e);
            } catch (IllegalStateException e) {
                Log.e(TAG, "Failed to getStatsMetadata in statsmanager");
                throw new StatsUnavailableException(e.getMessage(), e);
            }
        }
    }

    // TODO: Temporary for backwards compatibility. Remove.
    /**
     * @deprecated Use {@link #getStatsMetadata()}
     */
    @Deprecated
    @RequiresPermission(allOf = { DUMP, PACKAGE_USAGE_STATS })
    public @Nullable byte[] getMetadata() {
        try {
            return getStatsMetadata();
        } catch (StatsUnavailableException e) {
            return null;
        }
    }

    /**
     * Returns the experiments IDs registered with statsd, or an empty array if there aren't any.
     *
     * @throws StatsUnavailableException if unsuccessful due to failing to connect to stats service
     */
    @RequiresPermission(allOf = {DUMP, PACKAGE_USAGE_STATS})
    public long[] getRegisteredExperimentIds()
            throws StatsUnavailableException {
        synchronized (sLock) {
            try {
                IStatsManagerService service = getIStatsManagerServiceLocked();
                return service.getRegisteredExperimentIds();
            } catch (RemoteException e) {
                if (DEBUG) {
                    Log.d(TAG,
                            "Failed to connect to StatsManagerService when getting "
                                    + "registered experiment IDs");
                }
                throw new StatsUnavailableException("could not connect", e);
            } catch (IllegalStateException e) {
                Log.e(TAG, "Failed to getRegisteredExperimentIds in statsmanager");
                throw new StatsUnavailableException(e.getMessage(), e);
            }
        }
    }

    /**
     * Sets a callback for an atom when that atom is to be pulled. The stats service will
     * invoke pullData in the callback when the stats service determines that this atom needs to be
     * pulled. This method should not be called by third-party apps.
     *
     * @param atomTag           The tag of the atom for this puller callback.
     * @param metadata          Optional metadata specifying the timeout, cool down time, and
     *                          additive fields for mapping isolated to host uids.
     * @param executor          The executor in which to run the callback.
     * @param callback          The callback to be invoked when the stats service pulls the atom.
     *
     */
    @RequiresPermission(android.Manifest.permission.REGISTER_STATS_PULL_ATOM)
    public void setPullAtomCallback(int atomTag, @Nullable PullAtomMetadata metadata,
            @NonNull @CallbackExecutor Executor executor,
            @NonNull StatsPullAtomCallback callback) {
        long coolDownMillis =
                metadata == null ? DEFAULT_COOL_DOWN_MILLIS : metadata.mCoolDownMillis;
        long timeoutMillis = metadata == null ? DEFAULT_TIMEOUT_MILLIS : metadata.mTimeoutMillis;
        int[] additiveFields = metadata == null ? new int[0] : metadata.mAdditiveFields;
        if (additiveFields == null) {
            additiveFields = new int[0];
        }

        synchronized (sLock) {
            try {
                IStatsManagerService service = getIStatsManagerServiceLocked();
                PullAtomCallbackInternal rec =
                    new PullAtomCallbackInternal(atomTag, callback, executor);
                service.registerPullAtomCallback(
                        atomTag, coolDownMillis, timeoutMillis, additiveFields, rec);
            } catch (RemoteException e) {
                throw new RuntimeException("Unable to register pull callback", e);
            }
        }
    }

    /**
     * Clears a callback for an atom when that atom is to be pulled. Note that any ongoing
     * pulls will still occur. This method should not be called by third-party apps.
     *
     * @param atomTag           The tag of the atom of which to unregister
     *
     */
    @RequiresPermission(android.Manifest.permission.REGISTER_STATS_PULL_ATOM)
    public void clearPullAtomCallback(int atomTag) {
        synchronized (sLock) {
            try {
                IStatsManagerService service = getIStatsManagerServiceLocked();
                service.unregisterPullAtomCallback(atomTag);
            } catch (RemoteException e) {
                throw new RuntimeException("Unable to unregister pull atom callback");
            }
        }
    }

    private static class PullAtomCallbackInternal extends IPullAtomCallback.Stub {
        public final int mAtomId;
        public final StatsPullAtomCallback mCallback;
        public final Executor mExecutor;

        PullAtomCallbackInternal(int atomId, StatsPullAtomCallback callback, Executor executor) {
            mAtomId = atomId;
            mCallback = callback;
            mExecutor = executor;
        }

        @Override
        public void onPullAtom(int atomTag, IPullAtomResultReceiver resultReceiver) {
            long token = Binder.clearCallingIdentity();
            try {
                mExecutor.execute(() -> {
                    List<StatsEvent> data = new ArrayList<>();
                    int successInt = mCallback.onPullAtom(atomTag, data);
                    boolean success = successInt == PULL_SUCCESS;
                    StatsEventParcel[] parcels = new StatsEventParcel[data.size()];
                    for (int i = 0; i < data.size(); i++) {
                        parcels[i] = new StatsEventParcel();
                        parcels[i].buffer = data.get(i).getBytes();
                    }
                    try {
                        resultReceiver.pullFinished(atomTag, success, parcels);
                    } catch (RemoteException e) {
                        Log.w(TAG, "StatsPullResultReceiver failed for tag " + mAtomId);
                    }
                });
            } finally {
                Binder.restoreCallingIdentity(token);
            }
        }
    }

    /**
     * Metadata required for registering a StatsPullAtomCallback.
     * All fields are optional, and defaults will be used for fields that are unspecified.
     *
     */
    public static class PullAtomMetadata {
        private final long mCoolDownMillis;
        private final long mTimeoutMillis;
        private final int[] mAdditiveFields;

        // Private Constructor for builder
        private PullAtomMetadata(long coolDownMillis, long timeoutMillis, int[] additiveFields) {
            mCoolDownMillis = coolDownMillis;
            mTimeoutMillis = timeoutMillis;
            mAdditiveFields = additiveFields;
        }

        /**
         *  Builder for PullAtomMetadata.
         */
        public static class Builder {
            private long mCoolDownMillis;
            private long mTimeoutMillis;
            private int[] mAdditiveFields;

            /**
             * Returns a new PullAtomMetadata.Builder object for constructing PullAtomMetadata for
             * StatsManager#registerPullAtomCallback
             */
            public Builder() {
                mCoolDownMillis = DEFAULT_COOL_DOWN_MILLIS;
                mTimeoutMillis = DEFAULT_TIMEOUT_MILLIS;
                mAdditiveFields = null;
            }

            /**
             * Set the cool down time of the pull in milliseconds. If two successive pulls are
             * issued within the cool down, a cached version of the first pull will be used for the
             * second pull. The minimum allowed cool down is 1 second.
             */
            @NonNull
            public Builder setCoolDownMillis(long coolDownMillis) {
                mCoolDownMillis = coolDownMillis;
                return this;
            }

            /**
             * Set the maximum time the pull can take in milliseconds. The maximum allowed timeout
             * is 10 seconds.
             */
            @NonNull
            public Builder setTimeoutMillis(long timeoutMillis) {
                mTimeoutMillis = timeoutMillis;
                return this;
            }

            /**
             * Set the additive fields of this pulled atom.
             *
             * This is only applicable for atoms which have a uid field. When tasks are run in
             * isolated processes, the data will be attributed to the host uid. Additive fields
             * will be combined when the non-additive fields are the same.
             */
            @NonNull
            public Builder setAdditiveFields(@NonNull int[] additiveFields) {
                mAdditiveFields = additiveFields;
                return this;
            }

            /**
             * Builds and returns a PullAtomMetadata object with the values set in the builder and
             * defaults for unset fields.
             */
            @NonNull
            public PullAtomMetadata build() {
                return new PullAtomMetadata(mCoolDownMillis, mTimeoutMillis, mAdditiveFields);
            }
        }

        /**
         * Return the cool down time of this pull in milliseconds.
         */
        public long getCoolDownMillis() {
            return mCoolDownMillis;
        }

        /**
         * Return the maximum amount of time this pull can take in milliseconds.
         */
        public long getTimeoutMillis() {
            return mTimeoutMillis;
        }

        /**
         * Return the additive fields of this pulled atom.
         *
         * This is only applicable for atoms that have a uid field. When tasks are run in
         * isolated processes, the data will be attributed to the host uid. Additive fields
         * will be combined when the non-additive fields are the same.
         */
        @Nullable
        public int[] getAdditiveFields() {
            return mAdditiveFields;
        }
    }

    /**
     * Callback interface for pulling atoms requested by the stats service.
     *
     */
    public interface StatsPullAtomCallback {
        /**
         * Pull data for the specified atom tag, filling in the provided list of StatsEvent data.
         * @return {@link #PULL_SUCCESS} if the pull was successful, or {@link #PULL_SKIP} if not.
         */
        int onPullAtom(int atomTag, @NonNull List<StatsEvent> data);
    }

    @GuardedBy("sLock")
    private IStatsManagerService getIStatsManagerServiceLocked() {
        if (mStatsManagerService != null) {
            return mStatsManagerService;
        }
        mStatsManagerService = IStatsManagerService.Stub.asInterface(
                StatsFrameworkInitializer
                .getStatsServiceManager()
                .getStatsManagerServiceRegisterer()
                .get());
        return mStatsManagerService;
    }

    /**
     * Exception thrown when communication with the stats service fails (eg if it is not available).
     * This might be thrown early during boot before the stats service has started or if it crashed.
     */
    public static class StatsUnavailableException extends AndroidException {
        public StatsUnavailableException(String reason) {
            super("Failed to connect to statsd: " + reason);
        }

        public StatsUnavailableException(String reason, Throwable e) {
            super("Failed to connect to statsd: " + reason, e);
        }
    }
}