content: /*
   * Copyright (C) 2011 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.widget;
  
  import android.annotation.UnsupportedAppUsage;
  import android.app.ActivityManager;
  import android.content.ComponentName;
  import android.content.Context;
  import android.content.Intent;
  import android.content.pm.ActivityInfo;
  import android.content.pm.PackageManager;
  import android.content.pm.ResolveInfo;
  import android.database.DataSetObservable;
  import android.os.AsyncTask;
  import android.text.TextUtils;
  import android.util.Log;
  import android.util.Xml;
  
  import com.android.internal.content.PackageMonitor;
  
  import org.xmlpull.v1.XmlPullParser;
  import org.xmlpull.v1.XmlPullParserException;
  import org.xmlpull.v1.XmlSerializer;
  
  import java.io.FileInputStream;
  import java.io.FileNotFoundException;
  import java.io.FileOutputStream;
  import java.io.IOException;
  import java.math.BigDecimal;
  import java.nio.charset.StandardCharsets;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  /**
   * <p>
   * This class represents a data model for choosing a component for handing a
   * given {@link Intent}. The model is responsible for querying the system for
   * activities that can handle the given intent and order found activities
   * based on historical data of previous choices. The historical data is stored
   * in an application private file. If a client does not want to have persistent
   * choice history the file can be omitted, thus the activities will be ordered
   * based on historical usage for the current session.
   * <p>
   * </p>
   * For each backing history file there is a singleton instance of this class. Thus,
   * several clients that specify the same history file will share the same model. Note
   * that if multiple clients are sharing the same model they should implement semantically
   * equivalent functionality since setting the model intent will change the found
   * activities and they may be inconsistent with the functionality of some of the clients.
   * For example, choosing a share activity can be implemented by a single backing
   * model and two different views for performing the selection. If however, one of the
   * views is used for sharing but the other for importing, for example, then each
   * view should be backed by a separate model.
   * </p>
   * <p>
   * The way clients interact with this class is as follows:
   * </p>
   * <p>
   * <pre>
   * <code>
   *  // Get a model and set it to a couple of clients with semantically similar function.
   *  ActivityChooserModel dataModel =
   *      ActivityChooserModel.get(context, "task_specific_history_file_name.xml");
   *
   *  ActivityChooserModelClient modelClient1 = getActivityChooserModelClient1();
   *  modelClient1.setActivityChooserModel(dataModel);
   *
   *  ActivityChooserModelClient modelClient2 = getActivityChooserModelClient2();
   *  modelClient2.setActivityChooserModel(dataModel);
   *
   *  // Set an intent to choose a an activity for.
   *  dataModel.setIntent(intent);
   * <pre>
   * <code>
   * </p>
   * <p>
   * <strong>Note:</strong> This class is thread safe.
   * </p>
   *
   * @hide
   */
  public class ActivityChooserModel extends DataSetObservable {
  
      /**
       * Client that utilizes an {@link ActivityChooserModel}.
       */
      public interface ActivityChooserModelClient {
  
          /**
           * Sets the {@link ActivityChooserModel}.
           *
           * @param dataModel The model.
           */
          public void setActivityChooserModel(ActivityChooserModel dataModel);
      }
  
      /**
       * Defines a sorter that is responsible for sorting the activities
       * based on the provided historical choices and an intent.
       */
      public interface ActivitySorter {
  
          /**
           * Sorts the <code>activities</code> in descending order of relevance
           * based on previous history and an intent.
           *
           * @param intent The {@link Intent}.
           * @param activities Activities to be sorted.
           * @param historicalRecords Historical records.
           */
          // This cannot be done by a simple comparator since an Activity weight
          // is computed from history. Note that Activity implements Comparable.
          public void sort(Intent intent, List<ActivityResolveInfo> activities,
                  List<HistoricalRecord> historicalRecords);
      }
  
      /**
       * Listener for choosing an activity.
       */
      public interface OnChooseActivityListener {
  
          /**
           * Called when an activity has been chosen. The client can decide whether
           * an activity can be chosen and if so the caller of
           * {@link ActivityChooserModel#chooseActivity(int)} will receive and {@link Intent}
           * for launching it.
           * <p>
           * <strong>Note:</strong> Modifying the intent is not permitted and
           *     any changes to the latter will be ignored.
           * </p>
           *
           * @param host The listener's host model.
           * @param intent The intent for launching the chosen activity.
           * @return Whether the intent is handled and should not be delivered to clients.
           *
           * @see ActivityChooserModel#chooseActivity(int)
           */
          public boolean onChooseActivity(ActivityChooserModel host, Intent intent);
      }
  
      /**
       * Flag for selecting debug mode.
       */
      private static final boolean DEBUG = false;
  
      /**
       * Tag used for logging.
       */
      private static final String LOG_TAG = ActivityChooserModel.class.getSimpleName();
  
      /**
       * The root tag in the history file.
       */
      private static final String TAG_HISTORICAL_RECORDS = "historical-records";
  
      /**
       * The tag for a record in the history file.
       */
      private static final String TAG_HISTORICAL_RECORD = "historical-record";
  
      /**
       * Attribute for the activity.
       */
      private static final String ATTRIBUTE_ACTIVITY = "activity";
  
      /**
       * Attribute for the choice time.
       */
      private static final String ATTRIBUTE_TIME = "time";
  
      /**
       * Attribute for the choice weight.
       */
      private static final String ATTRIBUTE_WEIGHT = "weight";
  
      /**
       * The default name of the choice history file.
       */
      public static final String DEFAULT_HISTORY_FILE_NAME =
          "activity_choser_model_history.xml";
  
      /**
       * The default maximal length of the choice history.
       */
      public static final int DEFAULT_HISTORY_MAX_LENGTH = 50;
  
      /**
       * The amount with which to inflate a chosen activity when set as default.
       */
      private static final int DEFAULT_ACTIVITY_INFLATION = 5;
  
      /**
       * Default weight for a choice record.
       */
      private static final float DEFAULT_HISTORICAL_RECORD_WEIGHT = 1.0f;
  
      /**
       * The extension of the history file.
       */
      private static final String HISTORY_FILE_EXTENSION = ".xml";
  
      /**
       * An invalid item index.
       */
      private static final int INVALID_INDEX = -1;
  
      /**
       * Lock to guard the model registry.
       */
      private static final Object sRegistryLock = new Object();
  
      /**
       * This the registry for data models.
       */
      private static final Map<String, ActivityChooserModel> sDataModelRegistry =
          new HashMap<String, ActivityChooserModel>();
  
      /**
       * Lock for synchronizing on this instance.
       */
      private final Object mInstanceLock = new Object();
  
      /**
       * List of activities that can handle the current intent.
       */
      private final List<ActivityResolveInfo> mActivities = new ArrayList<ActivityResolveInfo>();
  
      /**
       * List with historical choice records.
       */
      private final List<HistoricalRecord> mHistoricalRecords = new ArrayList<HistoricalRecord>();
  
      /**
       * Monitor for added and removed packages.
       */
      private final PackageMonitor mPackageMonitor = new DataModelPackageMonitor();
  
      /**
       * Context for accessing resources.
       */
      private final Context mContext;
  
      /**
       * The name of the history file that backs this model.
       */
      private final String mHistoryFileName;
  
      /**
       * The intent for which a activity is being chosen.
       */
      private Intent mIntent;
  
      /**
       * The sorter for ordering activities based on intent and past choices.
       */
      private ActivitySorter mActivitySorter = new DefaultSorter();
  
      /**
       * The maximal length of the choice history.
       */
      private int mHistoryMaxSize = DEFAULT_HISTORY_MAX_LENGTH;
  
      /**
       * Flag whether choice history can be read. In general many clients can
       * share the same data model and {@link #readHistoricalDataIfNeeded()} may be called
       * by arbitrary of them any number of times. Therefore, this class guarantees
       * that the very first read succeeds and subsequent reads can be performed
       * only after a call to {@link #persistHistoricalDataIfNeeded()} followed by change
       * of the share records.
       */
      private boolean mCanReadHistoricalData = true;
  
      /**
       * Flag whether the choice history was read. This is used to enforce that
       * before calling {@link #persistHistoricalDataIfNeeded()} a call to
       * {@link #persistHistoricalDataIfNeeded()} has been made. This aims to avoid a
       * scenario in which a choice history file exits, it is not read yet and
       * it is overwritten. Note that always all historical records are read in
       * full and the file is rewritten. This is necessary since we need to
       * purge old records that are outside of the sliding window of past choices.
       */
      private boolean mReadShareHistoryCalled = false;
  
      /**
       * Flag whether the choice records have changed. In general many clients can
       * share the same data model and {@link #persistHistoricalDataIfNeeded()} may be called
       * by arbitrary of them any number of times. Therefore, this class guarantees
       * that choice history will be persisted only if it has changed.
       */
      private boolean mHistoricalRecordsChanged = true;
  
      /**
       * Flag whether to reload the activities for the current intent.
       */
      private boolean mReloadActivities = false;
  
      /**
       * Policy for controlling how the model handles chosen activities.
       */
      private OnChooseActivityListener mActivityChoserModelPolicy;
  
      /**
       * Gets the data model backed by the contents of the provided file with historical data.
       * Note that only one data model is backed by a given file, thus multiple calls with
       * the same file name will return the same model instance. If no such instance is present
       * it is created.
       * <p>
       * <strong>Note:</strong> To use the default historical data file clients should explicitly
       * pass as file name {@link #DEFAULT_HISTORY_FILE_NAME}. If no persistence of the choice
       * history is desired clients should pass <code>null</code> for the file name. In such
       * case a new model is returned for each invocation.
       * </p>
       *
       * <p>
       * <strong>Always use difference historical data files for semantically different actions.
       * For example, sharing is different from importing.</strong>
       * </p>
       *
       * @param context Context for loading resources.
       * @param historyFileName File name with choice history, <code>null</code>
       *        if the model should not be backed by a file. In this case the activities
       *        will be ordered only by data from the current session.
       *
       * @return The model.
       */
      @UnsupportedAppUsage
      public static ActivityChooserModel get(Context context, String historyFileName) {
          synchronized (sRegistryLock) {
              ActivityChooserModel dataModel = sDataModelRegistry.get(historyFileName);
              if (dataModel == null) {
                  dataModel = new ActivityChooserModel(context, historyFileName);
                  sDataModelRegistry.put(historyFileName, dataModel);
              }
              return dataModel;
          }
      }
  
      /**
       * Creates a new instance.
       *
       * @param context Context for loading resources.
       * @param historyFileName The history XML file.
       */
      private ActivityChooserModel(Context context, String historyFileName) {
          mContext = context.getApplicationContext();
          if (!TextUtils.isEmpty(historyFileName)
                  && !historyFileName.endsWith(HISTORY_FILE_EXTENSION)) {
              mHistoryFileName = historyFileName + HISTORY_FILE_EXTENSION;
          } else {
              mHistoryFileName = historyFileName;
          }
          mPackageMonitor.register(mContext, null, true);
      }
  
      /**
       * Sets an intent for which to choose a activity.
       * <p>
       * <strong>Note:</strong> Clients must set only semantically similar
       * intents for each data model.
       * <p>
       *
       * @param intent The intent.
       */
      @UnsupportedAppUsage
      public void setIntent(Intent intent) {
          synchronized (mInstanceLock) {
              if (mIntent == intent) {
                  return;
              }
              mIntent = intent;
              mReloadActivities = true;
              ensureConsistentState();
          }
      }
  
      /**
       * Gets the intent for which a activity is being chosen.
       *
       * @return The intent.
       */
      public Intent getIntent() {
          synchronized (mInstanceLock) {
              return mIntent;
          }
      }
  
      /**
       * Gets the number of activities that can handle the intent.
       *
       * @return The activity count.
       *
       * @see #setIntent(Intent)
       */
      @UnsupportedAppUsage
      public int getActivityCount() {
          synchronized (mInstanceLock) {
              ensureConsistentState();
              return mActivities.size();
          }
      }
  
      /**
       * Gets an activity at a given index.
       *
       * @return The activity.
       *
       * @see ActivityResolveInfo
       * @see #setIntent(Intent)
       */
      @UnsupportedAppUsage
      public ResolveInfo getActivity(int index) {
          synchronized (mInstanceLock) {
              ensureConsistentState();
              return mActivities.get(index).resolveInfo;
          }
      }
  
      /**
       * Gets the index of a the given activity.
       *
       * @param activity The activity index.
       *
       * @return The index if found, -1 otherwise.
       */
      public int getActivityIndex(ResolveInfo activity) {
          synchronized (mInstanceLock) {
              ensureConsistentState();
              List<ActivityResolveInfo> activities = mActivities;
              final int activityCount = activities.size();
              for (int i = 0; i < activityCount; i++) {
                  ActivityResolveInfo currentActivity = activities.get(i);
                  if (currentActivity.resolveInfo == activity) {
                      return i;
                  }
              }
              return INVALID_INDEX;
          }
      }
  
      /**
       * Chooses a activity to handle the current intent. This will result in
       * adding a historical record for that action and construct intent with
       * its component name set such that it can be immediately started by the
       * client.
       * <p>
       * <strong>Note:</strong> By calling this method the client guarantees
       * that the returned intent will be started. This intent is returned to
       * the client solely to let additional customization before the start.
       * </p>
       *
       * @return An {@link Intent} for launching the activity or null if the
       *         policy has consumed the intent or there is not current intent
       *         set via {@link #setIntent(Intent)}.
       *
       * @see HistoricalRecord
       * @see OnChooseActivityListener
       */
      @UnsupportedAppUsage
      public Intent chooseActivity(int index) {
          synchronized (mInstanceLock) {
              if (mIntent == null) {
                  return null;
              }
  
              ensureConsistentState();
  
              ActivityResolveInfo chosenActivity = mActivities.get(index);
  
              ComponentName chosenName = new ComponentName(
                      chosenActivity.resolveInfo.activityInfo.packageName,
                      chosenActivity.resolveInfo.activityInfo.name);
  
              Intent choiceIntent = new Intent(mIntent);
              choiceIntent.setComponent(chosenName);
  
              if (mActivityChoserModelPolicy != null) {
                  // Do not allow the policy to change the intent.
                  Intent choiceIntentCopy = new Intent(choiceIntent);
                  final boolean handled = mActivityChoserModelPolicy.onChooseActivity(this,
                          choiceIntentCopy);
                  if (handled) {
                      return null;
                  }
              }
  
              HistoricalRecord historicalRecord = new HistoricalRecord(chosenName,
                      System.currentTimeMillis(), DEFAULT_HISTORICAL_RECORD_WEIGHT);
              addHisoricalRecord(historicalRecord);
  
              return choiceIntent;
          }
      }
  
      /**
       * Sets the listener for choosing an activity.
       *
       * @param listener The listener.
       */
      @UnsupportedAppUsage
      public void setOnChooseActivityListener(OnChooseActivityListener listener) {
          synchronized (mInstanceLock) {
              mActivityChoserModelPolicy = listener;
          }
      }
  
      /**
       * Gets the default activity, The default activity is defined as the one
       * with highest rank i.e. the first one in the list of activities that can
       * handle the intent.
       *
       * @return The default activity, <code>null</code> id not activities.
       *
       * @see #getActivity(int)
       */
      public ResolveInfo getDefaultActivity() {
          synchronized (mInstanceLock) {
              ensureConsistentState();
              if (!mActivities.isEmpty()) {
                  return mActivities.get(0).resolveInfo;
              }
          }
          return null;
      }
  
      /**
       * Sets the default activity. The default activity is set by adding a
       * historical record with weight high enough that this activity will
       * become the highest ranked. Such a strategy guarantees that the default
       * will eventually change if not used. Also the weight of the record for
       * setting a default is inflated with a constant amount to guarantee that
       * it will stay as default for awhile.
       *
       * @param index The index of the activity to set as default.
       */
      public void setDefaultActivity(int index) {
          synchronized (mInstanceLock) {
              ensureConsistentState();
  
              ActivityResolveInfo newDefaultActivity = mActivities.get(index);
              ActivityResolveInfo oldDefaultActivity = mActivities.get(0);
  
              final float weight;
              if (oldDefaultActivity != null) {
                  // Add a record with weight enough to boost the chosen at the top.
                  weight = oldDefaultActivity.weight - newDefaultActivity.weight
                      + DEFAULT_ACTIVITY_INFLATION;
              } else {
                  weight = DEFAULT_HISTORICAL_RECORD_WEIGHT;
              }
  
              ComponentName defaultName = new ComponentName(
                      newDefaultActivity.resolveInfo.activityInfo.packageName,
                      newDefaultActivity.resolveInfo.activityInfo.name);
              HistoricalRecord historicalRecord = new HistoricalRecord(defaultName,
                      System.currentTimeMillis(), weight);
              addHisoricalRecord(historicalRecord);
          }
      }
  
      /**
       * Persists the history data to the backing file if the latter
       * was provided. Calling this method before a call to {@link #readHistoricalDataIfNeeded()}
       * throws an exception. Calling this method more than one without choosing an
       * activity has not effect.
       *
       * @throws IllegalStateException If this method is called before a call to
       *         {@link #readHistoricalDataIfNeeded()}.
       */
      private void persistHistoricalDataIfNeeded() {
          if (!mReadShareHistoryCalled) {
              throw new IllegalStateException("No preceding call to #readHistoricalData");
          }
          if (!mHistoricalRecordsChanged) {
              return;
          }
          mHistoricalRecordsChanged = false;
          if (!TextUtils.isEmpty(mHistoryFileName)) {
              new PersistHistoryAsyncTask().executeOnExecutor(AsyncTask.SERIAL_EXECUTOR,
                      new ArrayList<HistoricalRecord>(mHistoricalRecords), mHistoryFileName);
          }
      }
  
      /**
       * Sets the sorter for ordering activities based on historical data and an intent.
       *
       * @param activitySorter The sorter.
       *
       * @see ActivitySorter
       */
      public void setActivitySorter(ActivitySorter activitySorter) {
          synchronized (mInstanceLock) {
              if (mActivitySorter == activitySorter) {
                  return;
              }
              mActivitySorter = activitySorter;
              if (sortActivitiesIfNeeded()) {
                  notifyChanged();
              }
          }
      }
  
      /**
       * Sets the maximal size of the historical data. Defaults to
       * {@link #DEFAULT_HISTORY_MAX_LENGTH}
       * <p>
       *   <strong>Note:</strong> Setting this property will immediately
       *   enforce the specified max history size by dropping enough old
       *   historical records to enforce the desired size. Thus, any
       *   records that exceed the history size will be discarded and
       *   irreversibly lost.
       * </p>
       *
       * @param historyMaxSize The max history size.
       */
      public void setHistoryMaxSize(int historyMaxSize) {
          synchronized (mInstanceLock) {
              if (mHistoryMaxSize == historyMaxSize) {
                  return;
              }
              mHistoryMaxSize = historyMaxSize;
              pruneExcessiveHistoricalRecordsIfNeeded();
              if (sortActivitiesIfNeeded()) {
                  notifyChanged();
              }
          }
      }
  
      /**
       * Gets the history max size.
       *
       * @return The history max size.
       */
      public int getHistoryMaxSize() {
          synchronized (mInstanceLock) {
              return mHistoryMaxSize;
          }
      }
  
      /**
       * Gets the history size.
       *
       * @return The history size.
       */
      public int getHistorySize() {
          synchronized (mInstanceLock) {
              ensureConsistentState();
              return mHistoricalRecords.size();
          }
      }
  
      @Override
      protected void finalize() throws Throwable {
          super.finalize();
          mPackageMonitor.unregister();
      }
  
      /**
       * Ensures the model is in a consistent state which is the
       * activities for the current intent have been loaded, the
       * most recent history has been read, and the activities
       * are sorted.
       */
      private void ensureConsistentState() {
          boolean stateChanged = loadActivitiesIfNeeded();
          stateChanged |= readHistoricalDataIfNeeded();
          pruneExcessiveHistoricalRecordsIfNeeded();
          if (stateChanged) {
              sortActivitiesIfNeeded();
              notifyChanged();
          }
      }
  
      /**
       * Sorts the activities if necessary which is if there is a
       * sorter, there are some activities to sort, and there is some
       * historical data.
       *
       * @return Whether sorting was performed.
       */
      private boolean sortActivitiesIfNeeded() {
          if (mActivitySorter != null && mIntent != null
                  && !mActivities.isEmpty() && !mHistoricalRecords.isEmpty()) {
              mActivitySorter.sort(mIntent, mActivities,
                      Collections.unmodifiableList(mHistoricalRecords));
              return true;
          }
          return false;
      }
  
      /**
       * Loads the activities for the current intent if needed which is
       * if they are not already loaded for the current intent.
       *
       * @return Whether loading was performed.
       */
      private boolean loadActivitiesIfNeeded() {
          if (mReloadActivities && mIntent != null) {
              mReloadActivities = false;
              mActivities.clear();
              List<ResolveInfo> resolveInfos = mContext.getPackageManager()
                      .queryIntentActivities(mIntent, 0);
              final int resolveInfoCount = resolveInfos.size();
              for (int i = 0; i < resolveInfoCount; i++) {
                  ResolveInfo resolveInfo = resolveInfos.get(i);
                  ActivityInfo activityInfo = resolveInfo.activityInfo;
                  if (ActivityManager.checkComponentPermission(activityInfo.permission,
                          android.os.Process.myUid(), activityInfo.applicationInfo.uid,
                          activityInfo.exported) == PackageManager.PERMISSION_GRANTED) {
                      mActivities.add(new ActivityResolveInfo(resolveInfo));
                  }
              }
              return true;
          }
          return false;
      }
  
      /**
       * Reads the historical data if necessary which is it has
       * changed, there is a history file, and there is not persist
       * in progress.
       *
       * @return Whether reading was performed.
       */
      private boolean readHistoricalDataIfNeeded() {
          if (mCanReadHistoricalData && mHistoricalRecordsChanged &&
                  !TextUtils.isEmpty(mHistoryFileName)) {
              mCanReadHistoricalData = false;
              mReadShareHistoryCalled = true;
              readHistoricalDataImpl();
              return true;
          }
          return false;
      }
  
      /**
       * Adds a historical record.
       *
       * @param historicalRecord The record to add.
       * @return True if the record was added.
       */
      private boolean addHisoricalRecord(HistoricalRecord historicalRecord) {
          final boolean added = mHistoricalRecords.add(historicalRecord);
          if (added) {
              mHistoricalRecordsChanged = true;
              pruneExcessiveHistoricalRecordsIfNeeded();
              persistHistoricalDataIfNeeded();
              sortActivitiesIfNeeded();
              notifyChanged();
          }
          return added;
      }
  
      /**
       * Prunes older excessive records to guarantee maxHistorySize.
       */
      private void pruneExcessiveHistoricalRecordsIfNeeded() {
          final int pruneCount = mHistoricalRecords.size() - mHistoryMaxSize;
          if (pruneCount <= 0) {
              return;
          }
          mHistoricalRecordsChanged = true;
          for (int i = 0; i < pruneCount; i++) {
              HistoricalRecord prunedRecord = mHistoricalRecords.remove(0);
              if (DEBUG) {
                  Log.i(LOG_TAG, "Pruned: " + prunedRecord);
              }
          }
      }
  
      /**
       * Represents a record in the history.
       */
      public final static class HistoricalRecord {
  
          /**
           * The activity name.
           */
          public final ComponentName activity;
  
          /**
           * The choice time.
           */
          public final long time;
  
          /**
           * The record weight.
           */
          public final float weight;
  
          /**
           * Creates a new instance.
           *
           * @param activityName The activity component name flattened to string.
           * @param time The time the activity was chosen.
           * @param weight The weight of the record.
           */
          public HistoricalRecord(String activityName, long time, float weight) {
              this(ComponentName.unflattenFromString(activityName), time, weight);
          }
  
          /**
           * Creates a new instance.
           *
           * @param activityName The activity name.
           * @param time The time the activity was chosen.
           * @param weight The weight of the record.
           */
          public HistoricalRecord(ComponentName activityName, long time, float weight) {
              this.activity = activityName;
              this.time = time;
              this.weight = weight;
          }
  
          @Override
          public int hashCode() {
              final int prime = 31;
              int result = 1;
              result = prime * result + ((activity == null) ? 0 : activity.hashCode());
              result = prime * result + (int) (time ^ (time >>> 32));
              result = prime * result + Float.floatToIntBits(weight);
              return result;
          }
  
          @Override
          public boolean equals(Object obj) {
              if (this == obj) {
                  return true;
              }
              if (obj == null) {
                  return false;
              }
              if (getClass() != obj.getClass()) {
                  return false;
              }
              HistoricalRecord other = (HistoricalRecord) obj;
              if (activity == null) {
                  if (other.activity != null) {
                      return false;
                  }
              } else if (!activity.equals(other.activity)) {
                  return false;
              }
              if (time != other.time) {
                  return false;
              }
              if (Float.floatToIntBits(weight) != Float.floatToIntBits(other.weight)) {
                  return false;
              }
              return true;
          }
  
          @Override
          public String toString() {
              StringBuilder builder = new StringBuilder();
              builder.append("[");
              builder.append("; activity:").append(activity);
              builder.append("; time:").append(time);
              builder.append("; weight:").append(new BigDecimal(weight));
              builder.append("]");
              return builder.toString();
          }
      }
  
      /**
       * Represents an activity.
       */
      public final class ActivityResolveInfo implements Comparable<ActivityResolveInfo> {
  
          /**
           * The {@link ResolveInfo} of the activity.
           */
          public final ResolveInfo resolveInfo;
  
          /**
           * Weight of the activity. Useful for sorting.
           */
          public float weight;
  
          /**
           * Creates a new instance.
           *
           * @param resolveInfo activity {@link ResolveInfo}.
           */
          public ActivityResolveInfo(ResolveInfo resolveInfo) {
              this.resolveInfo = resolveInfo;
          }
  
          @Override
          public int hashCode() {
              return 31 + Float.floatToIntBits(weight);
          }
  
          @Override
          public boolean equals(Object obj) {
              if (this == obj) {
                  return true;
              }
              if (obj == null) {
                  return false;
              }
              if (getClass() != obj.getClass()) {
                  return false;
              }
              ActivityResolveInfo other = (ActivityResolveInfo) obj;
              if (Float.floatToIntBits(weight) != Float.floatToIntBits(other.weight)) {
                  return false;
              }
              return true;
          }
  
          public int compareTo(ActivityResolveInfo another) {
               return  Float.floatToIntBits(another.weight) - Float.floatToIntBits(weight);
          }
  
          @Override
          public String toString() {
              StringBuilder builder = new StringBuilder();
              builder.append("[");
              builder.append("resolveInfo:").append(resolveInfo.toString());
              builder.append("; weight:").append(new BigDecimal(weight));
              builder.append("]");
              return builder.toString();
          }
      }
  
      /**
       * Default activity sorter implementation.
       */
      private final class DefaultSorter implements ActivitySorter {
          private static final float WEIGHT_DECAY_COEFFICIENT = 0.95f;
  
          private final Map<ComponentName, ActivityResolveInfo> mPackageNameToActivityMap =
                  new HashMap<ComponentName, ActivityResolveInfo>();
  
          public void sort(Intent intent, List<ActivityResolveInfo> activities,
                  List<HistoricalRecord> historicalRecords) {
              Map<ComponentName, ActivityResolveInfo> componentNameToActivityMap =
                      mPackageNameToActivityMap;
              componentNameToActivityMap.clear();
  
              final int activityCount = activities.size();
              for (int i = 0; i < activityCount; i++) {
                  ActivityResolveInfo activity = activities.get(i);
                  activity.weight = 0.0f;
                  ComponentName componentName = new ComponentName(
                          activity.resolveInfo.activityInfo.packageName,
                          activity.resolveInfo.activityInfo.name);
                  componentNameToActivityMap.put(componentName, activity);
              }
  
              final int lastShareIndex = historicalRecords.size() - 1;
              float nextRecordWeight = 1;
              for (int i = lastShareIndex; i >= 0; i--) {
                  HistoricalRecord historicalRecord = historicalRecords.get(i);
                  ComponentName componentName = historicalRecord.activity;
                  ActivityResolveInfo activity = componentNameToActivityMap.get(componentName);
                  if (activity != null) {
                      activity.weight += historicalRecord.weight * nextRecordWeight;
                      nextRecordWeight = nextRecordWeight * WEIGHT_DECAY_COEFFICIENT;
                  }
              }
  
              Collections.sort(activities);
  
              if (DEBUG) {
                  for (int i = 0; i < activityCount; i++) {
                      Log.i(LOG_TAG, "Sorted: " + activities.get(i));
                  }
              }
          }
      }
  
      private void readHistoricalDataImpl() {
          FileInputStream fis = null;
          try {
              fis = mContext.openFileInput(mHistoryFileName);
          } catch (FileNotFoundException fnfe) {
              if (DEBUG) {
                  Log.i(LOG_TAG, "Could not open historical records file: " + mHistoryFileName);
              }
              return;
          }
          try {
              XmlPullParser parser = Xml.newPullParser();
              parser.setInput(fis, StandardCharsets.UTF_8.name());
  
              int type = XmlPullParser.START_DOCUMENT;
              while (type != XmlPullParser.END_DOCUMENT && type != XmlPullParser.START_TAG) {
                  type = parser.next();
              }
  
              if (!TAG_HISTORICAL_RECORDS.equals(parser.getName())) {
                  throw new XmlPullParserException("Share records file does not start with "
                          + TAG_HISTORICAL_RECORDS + " tag.");
              }
  
              List<HistoricalRecord> historicalRecords = mHistoricalRecords;
              historicalRecords.clear();
  
              while (true) {
                  type = parser.next();
                  if (type == XmlPullParser.END_DOCUMENT) {
                      break;
                  }
                  if (type == XmlPullParser.END_TAG || type == XmlPullParser.TEXT) {
                      continue;
                  }
                  String nodeName = parser.getName();
                  if (!TAG_HISTORICAL_RECORD.equals(nodeName)) {
                      throw new XmlPullParserException("Share records file not well-formed.");
                  }
  
                  String activity = parser.getAttributeValue(null, ATTRIBUTE_ACTIVITY);
                  final long time =
                      Long.parseLong(parser.getAttributeValue(null, ATTRIBUTE_TIME));
                  final float weight =
                      Float.parseFloat(parser.getAttributeValue(null, ATTRIBUTE_WEIGHT));
                   HistoricalRecord readRecord = new HistoricalRecord(activity, time, weight);
                  historicalRecords.add(readRecord);
  
                  if (DEBUG) {
                      Log.i(LOG_TAG, "Read " + readRecord.toString());
                  }
              }
  
              if (DEBUG) {
                  Log.i(LOG_TAG, "Read " + historicalRecords.size() + " historical records.");
              }
          } catch (XmlPullParserException xppe) {
              Log.e(LOG_TAG, "Error reading historical recrod file: " + mHistoryFileName, xppe);
          } catch (IOException ioe) {
              Log.e(LOG_TAG, "Error reading historical recrod file: " + mHistoryFileName, ioe);
          } finally {
              if (fis != null) {
                  try {
                      fis.close();
                  } catch (IOException ioe) {
                      /* ignore */
                  }
              }
          }
      }
  
      /**
       * Command for persisting the historical records to a file off the UI thread.
       */
      private final class PersistHistoryAsyncTask extends AsyncTask<Object, Void, Void> {
  
          @Override
          @SuppressWarnings("unchecked")
          public Void doInBackground(Object... args) {
              List<HistoricalRecord> historicalRecords = (List<HistoricalRecord>) args[0];
              String hostoryFileName = (String) args[1];
  
              FileOutputStream fos = null;
  
              try {
                  fos = mContext.openFileOutput(hostoryFileName, Context.MODE_PRIVATE);
              } catch (FileNotFoundException fnfe) {
                  Log.e(LOG_TAG, "Error writing historical recrod file: " + hostoryFileName, fnfe);
                  return null;
              }
  
              XmlSerializer serializer = Xml.newSerializer();
  
              try {
                  serializer.setOutput(fos, null);
                  serializer.startDocument(StandardCharsets.UTF_8.name(), true);
                  serializer.startTag(null, TAG_HISTORICAL_RECORDS);
  
                  final int recordCount = historicalRecords.size();
                  for (int i = 0; i < recordCount; i++) {
                      HistoricalRecord record = historicalRecords.remove(0);
                      serializer.startTag(null, TAG_HISTORICAL_RECORD);
                      serializer.attribute(null, ATTRIBUTE_ACTIVITY,
                              record.activity.flattenToString());
                      serializer.attribute(null, ATTRIBUTE_TIME, String.valueOf(record.time));
                      serializer.attribute(null, ATTRIBUTE_WEIGHT, String.valueOf(record.weight));
                      serializer.endTag(null, TAG_HISTORICAL_RECORD);
                      if (DEBUG) {
                          Log.i(LOG_TAG, "Wrote " + record.toString());
                      }
                  }
  
                  serializer.endTag(null, TAG_HISTORICAL_RECORDS);
                  serializer.endDocument();
  
                  if (DEBUG) {
                      Log.i(LOG_TAG, "Wrote " + recordCount + " historical records.");
                  }
              } catch (IllegalArgumentException iae) {
                  Log.e(LOG_TAG, "Error writing historical recrod file: " + mHistoryFileName, iae);
              } catch (IllegalStateException ise) {
                  Log.e(LOG_TAG, "Error writing historical recrod file: " + mHistoryFileName, ise);
              } catch (IOException ioe) {
                  Log.e(LOG_TAG, "Error writing historical recrod file: " + mHistoryFileName, ioe);
              } finally {
                  mCanReadHistoricalData = true;
                  if (fos != null) {
                      try {
                          fos.close();
                      } catch (IOException e) {
                          /* ignore */
                      }
                  }
              }
              return null;
          }
      }
  
      /**
       * Keeps in sync the historical records and activities with the installed applications.
       */
      private final class DataModelPackageMonitor extends PackageMonitor {
  
          @Override
          public void onSomePackagesChanged() {
              mReloadActivities = true;
          }
      }
  }
  