Factor freqeuncy and mimetype of past sharings, foreground app into

sharesheet model. Promote most frequent sharable apps to tackle cold
start issue when device doesn't hold enough sharing history.

Bug: 149822311
Test: manual test Sharesheet ranking on device
Test: atest com.android.server.people.prediction.ShareTargetPredictorTest
Test: atest com.android.server.people.prediction.SharesheetModelHelperTest
Test: atest com.android.server.people.data.UsageStatsQueryHelperTest
Change-Id: I6eb764448c0619cbc3b320b5f6432f559d1a15e1

4 files changed, 523 insertions, 31 deletions

diff --git a/services/people/java/com/android/server/people/data/DataManager.java b/services/people/java/com/android/server/people/data/DataManager.java
index ae8d5743668a..136ee91dd685 100644
--- a/services/people/java/com/android/server/people/data/DataManager.java
+++ b/services/people/java/com/android/server/people/data/DataManager.java
@@ -26,6 +26,7 @@ import android.app.NotificationManager;
 import android.app.Person;
 import android.app.prediction.AppTarget;
 import android.app.prediction.AppTargetEvent;
+import android.app.usage.UsageEvents;
 import android.content.BroadcastReceiver;
 import android.content.ComponentName;
 import android.content.ContentResolver;
@@ -70,6 +71,7 @@ import com.android.server.notification.NotificationManagerInternal;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Executors;
@@ -237,6 +239,27 @@ public class DataManager {
         eventHistory.addEvent(new Event(System.currentTimeMillis(), eventType));
     }
 
+    /**
+     * Queries events for moving app to foreground between {@code startTime} and {@code endTime}.
+     */
+    @NonNull
+    public List<UsageEvents.Event> queryAppMovingToForegroundEvents(@UserIdInt int callingUserId,
+            long startTime, long endTime) {
+        return UsageStatsQueryHelper.queryAppMovingToForegroundEvents(callingUserId, startTime,
+                endTime);
+    }
+
+    /**
+     * Queries launch counts of apps within {@code packageNameFilter} between {@code startTime}
+     * and {@code endTime}.
+     */
+    @NonNull
+    public Map<String, Integer> queryAppLaunchCount(@UserIdInt int callingUserId, long startTime,
+            long endTime, Set<String> packageNameFilter) {
+        return UsageStatsQueryHelper.queryAppLaunchCount(callingUserId, startTime, endTime,
+                packageNameFilter);
+    }
+
     /** Prunes the data for the specified user. */
     public void pruneDataForUser(@UserIdInt int userId, @NonNull CancellationSignal signal) {
         UserData userData = getUnlockedUserData(userId);
@@ -382,7 +405,13 @@ public class DataManager {
         }
     }
 
-    private int mimeTypeToShareEventType(String mimeType) {
+    /**
+     * Converts {@code mimeType} to {@link Event.EventType}.
+     */
+    public int mimeTypeToShareEventType(String mimeType) {
+        if (mimeType == null) {
+            return Event.TYPE_SHARE_OTHER;
+        }
         if (mimeType.startsWith("text/")) {
             return Event.TYPE_SHARE_TEXT;
         } else if (mimeType.startsWith("image/")) {
diff --git a/services/people/java/com/android/server/people/data/UsageStatsQueryHelper.java b/services/people/java/com/android/server/people/data/UsageStatsQueryHelper.java
index 72f1abb70e34..6e6fea93c803 100644
--- a/services/people/java/com/android/server/people/data/UsageStatsQueryHelper.java
+++ b/services/people/java/com/android/server/people/data/UsageStatsQueryHelper.java
@@ -19,6 +19,8 @@ package com.android.server.people.data;
 import android.annotation.NonNull;
 import android.annotation.UserIdInt;
 import android.app.usage.UsageEvents;
+import android.app.usage.UsageStats;
+import android.app.usage.UsageStatsManager;
 import android.app.usage.UsageStatsManagerInternal;
 import android.content.ComponentName;
 import android.content.LocusId;
@@ -27,7 +29,10 @@ import android.util.ArrayMap;
 
 import com.android.server.LocalServices;
 
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import java.util.function.Function;
 
 /** A helper class that queries {@link UsageStatsManagerInternal}. */
@@ -46,7 +51,7 @@ class UsageStatsQueryHelper {
      */
     UsageStatsQueryHelper(@UserIdInt int userId,
             Function<String, PackageData> packageDataGetter) {
-        mUsageStatsManagerInternal = LocalServices.getService(UsageStatsManagerInternal.class);
+        mUsageStatsManagerInternal = getUsageStatsManagerInternal();
         mUserId = userId;
         mPackageDataGetter = packageDataGetter;
     }
@@ -106,6 +111,53 @@ class UsageStatsQueryHelper {
         return mLastEventTimestamp;
     }
 
+    /**
+     * Queries {@link UsageStatsManagerInternal} events for moving app to foreground between
+     * {@code startTime} and {@code endTime}.
+     *
+     * @return a list containing events moving app to foreground.
+     */
+    static List<UsageEvents.Event> queryAppMovingToForegroundEvents(@UserIdInt int userId,
+            long startTime, long endTime) {
+        List<UsageEvents.Event> res = new ArrayList<>();
+        UsageEvents usageEvents = getUsageStatsManagerInternal().queryEventsForUser(userId,
+                startTime, endTime,
+                UsageEvents.HIDE_SHORTCUT_EVENTS | UsageEvents.HIDE_LOCUS_EVENTS);
+        if (usageEvents == null) {
+            return res;
+        }
+        while (usageEvents.hasNextEvent()) {
+            UsageEvents.Event e = new UsageEvents.Event();
+            usageEvents.getNextEvent(e);
+            if (e.getEventType() == UsageEvents.Event.ACTIVITY_RESUMED) {
+                res.add(e);
+            }
+        }
+        return res;
+    }
+
+    /**
+     * Queries {@link UsageStatsManagerInternal} for launch count of apps within {@code
+     * packageNameFilter} between {@code startTime} and {@code endTime}.obfuscateInstantApps
+     *
+     * @return a map which keys are package names and values are app launch counts.
+     */
+    static Map<String, Integer> queryAppLaunchCount(@UserIdInt int userId, long startTime,
+            long endTime, Set<String> packageNameFilter) {
+        List<UsageStats> stats = getUsageStatsManagerInternal().queryUsageStatsForUser(userId,
+                UsageStatsManager.INTERVAL_BEST, startTime, endTime,
+                /* obfuscateInstantApps= */ false);
+        Map<String, Integer> aggregatedStats = new ArrayMap<>();
+        for (UsageStats stat : stats) {
+            String packageName = stat.getPackageName();
+            if (packageNameFilter.contains(packageName)) {
+                aggregatedStats.put(packageName,
+                        aggregatedStats.getOrDefault(packageName, 0) + stat.getAppLaunchCount());
+            }
+        }
+        return aggregatedStats;
+    }
+
     private void onInAppConversationEnded(@NonNull PackageData packageData,
             @NonNull UsageEvents.Event endEvent) {
         ComponentName activityName =
@@ -138,4 +190,8 @@ class UsageStatsQueryHelper {
                 EventStore.CATEGORY_LOCUS_ID_BASED, locusId.getId());
         eventHistory.addEvent(event);
     }
+
+    private static UsageStatsManagerInternal getUsageStatsManagerInternal() {
+        return LocalServices.getService(UsageStatsManagerInternal.class);
+    }
 }
diff --git a/services/people/java/com/android/server/people/prediction/ShareTargetPredictor.java b/services/people/java/com/android/server/people/prediction/ShareTargetPredictor.java
index 8e5d75be12b7..d09d0b379769 100644
--- a/services/people/java/com/android/server/people/prediction/ShareTargetPredictor.java
+++ b/services/people/java/com/android/server/people/prediction/ShareTargetPredictor.java
@@ -27,13 +27,11 @@ import android.app.prediction.AppTargetId;
 import android.content.IntentFilter;
 import android.content.pm.ShortcutInfo;
 import android.content.pm.ShortcutManager.ShareShortcutInfo;
-import android.util.Range;
 
 import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.app.ChooserActivity;
 import com.android.server.people.data.ConversationInfo;
 import com.android.server.people.data.DataManager;
-import com.android.server.people.data.Event;
 import com.android.server.people.data.EventHistory;
 import com.android.server.people.data.PackageData;
 
@@ -42,6 +40,9 @@ import java.util.Collections;
 import java.util.List;
 import java.util.function.Consumer;
 
+/**
+ * Predictor that predicts the {@link AppTarget} the user is most likely to open on share sheet.
+ */
 class ShareTargetPredictor extends AppTargetPredictor {
 
     private final IntentFilter mIntentFilter;
@@ -66,7 +67,9 @@ class ShareTargetPredictor extends AppTargetPredictor {
     @Override
     void predictTargets() {
         List<ShareTarget> shareTargets = getDirectShareTargets();
-        rankTargets(shareTargets);
+        SharesheetModelScorer.computeScore(shareTargets, getShareEventType(mIntentFilter),
+                System.currentTimeMillis());
+        Collections.sort(shareTargets, (t1, t2) -> -Float.compare(t1.getScore(), t2.getScore()));
         List<AppTarget> res = new ArrayList<>();
         for (int i = 0; i < Math.min(getPredictionContext().getPredictedTargetCount(),
                 shareTargets.size()); i++) {
@@ -80,36 +83,16 @@ class ShareTargetPredictor extends AppTargetPredictor {
     @Override
     void sortTargets(List<AppTarget> targets, Consumer<List<AppTarget>> callback) {
         List<ShareTarget> shareTargets = getAppShareTargets(targets);
-        rankTargets(shareTargets);
+        SharesheetModelScorer.computeScoreForAppShare(shareTargets,
+                getShareEventType(mIntentFilter), getPredictionContext().getPredictedTargetCount(),
+                System.currentTimeMillis(), getDataManager(),
+                mCallingUserId);
+        Collections.sort(shareTargets, (t1, t2) -> -Float.compare(t1.getScore(), t2.getScore()));
         List<AppTarget> appTargetList = new ArrayList<>();
         shareTargets.forEach(t -> appTargetList.add(t.getAppTarget()));
         callback.accept(appTargetList);
     }
 
-    private void rankTargets(List<ShareTarget> shareTargets) {
-        // Rank targets based on recency of sharing history only for the moment.
-        // TODO: Take more factors into ranking, e.g. frequency, mime type, foreground app.
-        Collections.sort(shareTargets, (t1, t2) -> {
-            if (t1.getEventHistory() == null) {
-                return 1;
-            }
-            if (t2.getEventHistory() == null) {
-                return -1;
-            }
-            Range<Long> timeSlot1 = t1.getEventHistory().getEventIndex(
-                    Event.SHARE_EVENT_TYPES).getMostRecentActiveTimeSlot();
-            Range<Long> timeSlot2 = t2.getEventHistory().getEventIndex(
-                    Event.SHARE_EVENT_TYPES).getMostRecentActiveTimeSlot();
-            if (timeSlot1 == null) {
-                return 1;
-            } else if (timeSlot2 == null) {
-                return -1;
-            } else {
-                return -Long.compare(timeSlot1.getUpper(), timeSlot2.getUpper());
-            }
-        });
-    }
-
     private List<ShareTarget> getDirectShareTargets() {
         List<ShareTarget> shareTargets = new ArrayList<>();
         List<ShareShortcutInfo> shareShortcuts =
@@ -153,6 +136,11 @@ class ShareTargetPredictor extends AppTargetPredictor {
         return shareTargets;
     }
 
+    private int getShareEventType(IntentFilter intentFilter) {
+        String mimeType = intentFilter != null ? intentFilter.getDataType(0) : null;
+        return getDataManager().mimeTypeToShareEventType(mimeType);
+    }
+
     @VisibleForTesting
     static class ShareTarget {
 
@@ -162,13 +150,16 @@ class ShareTargetPredictor extends AppTargetPredictor {
         private final EventHistory mEventHistory;
         @Nullable
         private final ConversationInfo mConversationInfo;
+        private float mScore;
 
-        private ShareTarget(@NonNull AppTarget appTarget,
+        @VisibleForTesting
+        ShareTarget(@NonNull AppTarget appTarget,
                 @Nullable EventHistory eventHistory,
                 @Nullable ConversationInfo conversationInfo) {
             mAppTarget = appTarget;
             mEventHistory = eventHistory;
             mConversationInfo = conversationInfo;
+            mScore = 0f;
         }
 
         @NonNull
@@ -188,5 +179,15 @@ class ShareTargetPredictor extends AppTargetPredictor {
         ConversationInfo getConversationInfo() {
             return mConversationInfo;
         }
+
+        @VisibleForTesting
+        float getScore() {
+            return mScore;
+        }
+
+        @VisibleForTesting
+        void setScore(float score) {
+            mScore = score;
+        }
     }
 }
diff --git a/services/people/java/com/android/server/people/prediction/SharesheetModelScorer.java b/services/people/java/com/android/server/people/prediction/SharesheetModelScorer.java
new file mode 100644
index 000000000000..0ac5724210da
--- /dev/null
+++ b/services/people/java/com/android/server/people/prediction/SharesheetModelScorer.java
@@ -0,0 +1,406 @@
+/*
+ * Copyright (C) 2020 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.server.people.prediction;
+
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+import android.annotation.UserIdInt;
+import android.app.usage.UsageEvents;
+import android.util.ArrayMap;
+import android.util.Pair;
+import android.util.Range;
+import android.util.Slog;
+
+import com.android.internal.annotations.VisibleForTesting;
+import com.android.internal.app.ChooserActivity;
+import com.android.server.people.data.DataManager;
+import com.android.server.people.data.Event;
+
+import java.time.Duration;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Map;
+import java.util.PriorityQueue;
+import java.util.concurrent.TimeUnit;
+
+/** Ranking scorer for Sharesheet targets. */
+class SharesheetModelScorer {
+
+    private static final String TAG = "SharesheetModelScorer";
+    private static final boolean DEBUG = false;
+    private static final Integer RECENCY_SCORE_COUNT = 6;
+    private static final float RECENCY_INITIAL_BASE_SCORE = 0.4F;
+    private static final float RECENCY_SCORE_INITIAL_DECAY = 0.05F;
+    private static final float RECENCY_SCORE_SUBSEQUENT_DECAY = 0.02F;
+    private static final long ONE_MONTH_WINDOW = TimeUnit.DAYS.toMillis(30);
+    private static final long FOREGROUND_APP_PROMO_TIME_WINDOW = TimeUnit.MINUTES.toMillis(10);
+    private static final float FREQUENTLY_USED_APP_SCORE_DECAY = 0.9F;
+    @VisibleForTesting
+    static final float FOREGROUND_APP_WEIGHT = 0F;
+    @VisibleForTesting
+    static final String CHOOSER_ACTIVITY = ChooserActivity.class.getSimpleName();
+
+    // Keep constructor private to avoid class being instantiated.
+    private SharesheetModelScorer() {
+    }
+
+    /**
+     * Computes each target's recency, frequency and frequency of the same {@code shareEventType}
+     * based on past sharing history. Update {@link ShareTargetPredictor.ShareTargetScore}.
+     */
+    static void computeScore(List<ShareTargetPredictor.ShareTarget> shareTargets,
+            int shareEventType, long now) {
+        if (shareTargets.isEmpty()) {
+            return;
+        }
+        float totalFreqScore = 0f;
+        int freqScoreCount = 0;
+        float totalMimeFreqScore = 0f;
+        int mimeFreqScoreCount = 0;
+        // Top of this heap has lowest rank.
+        PriorityQueue<Pair<ShareTargetRankingScore, Range<Long>>> recencyMinHeap =
+                new PriorityQueue<>(RECENCY_SCORE_COUNT,
+                        Comparator.comparingLong(p -> p.second.getUpper()));
+        List<ShareTargetRankingScore> scoreList = new ArrayList<>(shareTargets.size());
+        for (ShareTargetPredictor.ShareTarget target : shareTargets) {
+            ShareTargetRankingScore shareTargetScore = new ShareTargetRankingScore();
+            scoreList.add(shareTargetScore);
+            if (target.getEventHistory() == null) {
+                continue;
+            }
+            // Counts frequency
+            List<Range<Long>> timeSlots = target.getEventHistory().getEventIndex(
+                    Event.SHARE_EVENT_TYPES).getActiveTimeSlots();
+            if (!timeSlots.isEmpty()) {
+                for (Range<Long> timeSlot : timeSlots) {
+                    shareTargetScore.incrementFrequencyScore(
+                            getFreqDecayedOnElapsedTime(now - timeSlot.getLower()));
+                }
+                totalFreqScore += shareTargetScore.getFrequencyScore();
+                freqScoreCount++;
+            }
+            // Counts frequency for sharing same mime type
+            List<Range<Long>> timeSlotsOfSameType = target.getEventHistory().getEventIndex(
+                    shareEventType).getActiveTimeSlots();
+            if (!timeSlotsOfSameType.isEmpty()) {
+                for (Range<Long> timeSlot : timeSlotsOfSameType) {
+                    shareTargetScore.incrementMimeFrequencyScore(
+                            getFreqDecayedOnElapsedTime(now - timeSlot.getLower()));
+                }
+                totalMimeFreqScore += shareTargetScore.getMimeFrequencyScore();
+                mimeFreqScoreCount++;
+            }
+            // Records most recent targets
+            Range<Long> mostRecentTimeSlot = target.getEventHistory().getEventIndex(
+                    Event.SHARE_EVENT_TYPES).getMostRecentActiveTimeSlot();
+            if (mostRecentTimeSlot == null) {
+                continue;
+            }
+            if (recencyMinHeap.size() < RECENCY_SCORE_COUNT
+                    || mostRecentTimeSlot.getUpper() > recencyMinHeap.peek().second.getUpper()) {
+                if (recencyMinHeap.size() == RECENCY_SCORE_COUNT) {
+                    recencyMinHeap.poll();
+                }
+                recencyMinHeap.offer(new Pair(shareTargetScore, mostRecentTimeSlot));
+            }
+        }
+        // Calculates recency score
+        while (!recencyMinHeap.isEmpty()) {
+            float recencyScore = RECENCY_INITIAL_BASE_SCORE;
+            if (recencyMinHeap.size() > 1) {
+                recencyScore = RECENCY_INITIAL_BASE_SCORE - RECENCY_SCORE_INITIAL_DECAY
+                        - RECENCY_SCORE_SUBSEQUENT_DECAY * (recencyMinHeap.size() - 2);
+            }
+            recencyMinHeap.poll().first.setRecencyScore(recencyScore);
+        }
+
+        Float avgFreq = freqScoreCount != 0 ? totalFreqScore / freqScoreCount : 0f;
+        Float avgMimeFreq = mimeFreqScoreCount != 0 ? totalMimeFreqScore / mimeFreqScoreCount : 0f;
+        for (int i = 0; i < scoreList.size(); i++) {
+            ShareTargetPredictor.ShareTarget target = shareTargets.get(i);
+            ShareTargetRankingScore targetScore = scoreList.get(i);
+            // Normalizes freq and mimeFreq score
+            targetScore.setFrequencyScore(normalizeFreqScore(
+                    avgFreq.equals(0f) ? 0f : targetScore.getFrequencyScore() / avgFreq));
+            targetScore.setMimeFrequencyScore(normalizeMimeFreqScore(avgMimeFreq.equals(0f) ? 0f
+                    : targetScore.getMimeFrequencyScore() / avgMimeFreq));
+            // Calculates total score
+            targetScore.setTotalScore(
+                    probOR(probOR(targetScore.getRecencyScore(), targetScore.getFrequencyScore()),
+                            targetScore.getMimeFrequencyScore()));
+            target.setScore(targetScore.getTotalScore());
+
+            if (DEBUG) {
+                Slog.d(TAG, String.format(
+                        "SharesheetModel: packageName: %s, className: %s, shortcutId: %s, "
+                                + "recency:%.2f, freq_all:%.2f, freq_mime:%.2f, total:%.2f",
+                        target.getAppTarget().getPackageName(),
+                        target.getAppTarget().getClassName(),
+                        target.getAppTarget().getShortcutInfo() != null
+                                ? target.getAppTarget().getShortcutInfo().getId() : null,
+                        targetScore.getRecencyScore(),
+                        targetScore.getFrequencyScore(),
+                        targetScore.getMimeFrequencyScore(),
+                        targetScore.getTotalScore()));
+            }
+        }
+    }
+
+    /**
+     * Computes ranking score for app sharing. Update {@link ShareTargetPredictor.ShareTargetScore}.
+     */
+    static void computeScoreForAppShare(List<ShareTargetPredictor.ShareTarget> shareTargets,
+            int shareEventType, int targetsLimit, long now, @NonNull DataManager dataManager,
+            @UserIdInt int callingUserId) {
+        computeScore(shareTargets, shareEventType, now);
+        postProcess(shareTargets, targetsLimit, dataManager, callingUserId);
+    }
+
+    private static void postProcess(List<ShareTargetPredictor.ShareTarget> shareTargets,
+            int targetsLimit, @NonNull DataManager dataManager, @UserIdInt int callingUserId) {
+        // Populates a map which key is package name and value is list of shareTargets descended
+        // on total score.
+        Map<String, List<ShareTargetPredictor.ShareTarget>> shareTargetMap = new ArrayMap<>();
+        for (ShareTargetPredictor.ShareTarget shareTarget : shareTargets) {
+            String packageName = shareTarget.getAppTarget().getPackageName();
+            shareTargetMap.computeIfAbsent(packageName, key -> new ArrayList<>());
+            List<ShareTargetPredictor.ShareTarget> targetsList = shareTargetMap.get(packageName);
+            int index = 0;
+            while (index < targetsList.size()) {
+                if (shareTarget.getScore() > targetsList.get(index).getScore()) {
+                    break;
+                }
+                index++;
+            }
+            targetsList.add(index, shareTarget);
+        }
+        promoteForegroundApp(shareTargetMap, dataManager, callingUserId);
+        promoteFrequentlyUsedApps(shareTargetMap, targetsLimit, dataManager, callingUserId);
+    }
+
+    /**
+     * Promotes frequently used sharing apps, if recommended apps based on sharing history have not
+     * reached the limit (e.g. user did not share any content in last couple weeks)
+     */
+    private static void promoteFrequentlyUsedApps(
+            Map<String, List<ShareTargetPredictor.ShareTarget>> shareTargetMap, int targetsLimit,
+            @NonNull DataManager dataManager, @UserIdInt int callingUserId) {
+        int validPredictionNum = 0;
+        float minValidScore = 1f;
+        for (List<ShareTargetPredictor.ShareTarget> targets : shareTargetMap.values()) {
+            for (ShareTargetPredictor.ShareTarget target : targets) {
+                if (target.getScore() > 0f) {
+                    validPredictionNum++;
+                    minValidScore = Math.min(target.getScore(), minValidScore);
+                }
+            }
+        }
+        // Skips if recommended apps based on sharing history have already reached the limit.
+        if (validPredictionNum >= targetsLimit) {
+            return;
+        }
+        long now = System.currentTimeMillis();
+        Map<String, Integer> appLaunchCountsMap = dataManager.queryAppLaunchCount(
+                callingUserId, now - ONE_MONTH_WINDOW, now, shareTargetMap.keySet());
+        List<Pair<String, Integer>> appLaunchCounts = new ArrayList<>();
+        for (Map.Entry<String, Integer> entry : appLaunchCountsMap.entrySet()) {
+            if (entry.getValue() > 0) {
+                appLaunchCounts.add(new Pair(entry.getKey(), entry.getValue()));
+            }
+        }
+        Collections.sort(appLaunchCounts, (p1, p2) -> -Integer.compare(p1.second, p2.second));
+        for (Pair<String, Integer> entry : appLaunchCounts) {
+            if (!shareTargetMap.containsKey(entry.first)) {
+                continue;
+            }
+            ShareTargetPredictor.ShareTarget target = shareTargetMap.get(entry.first).get(0);
+            if (target.getScore() > 0f) {
+                continue;
+            }
+            minValidScore *= FREQUENTLY_USED_APP_SCORE_DECAY;
+            target.setScore(minValidScore);
+            if (DEBUG) {
+                Slog.d(TAG, String.format(
+                        "SharesheetModel: promoteFrequentUsedApps packageName: %s, className: %s,"
+                                + " total:%.2f",
+                        target.getAppTarget().getPackageName(),
+                        target.getAppTarget().getClassName(),
+                        target.getScore()));
+            }
+            validPredictionNum++;
+            if (validPredictionNum == targetsLimit) {
+                return;
+            }
+        }
+    }
+
+    /**
+     * Promotes the foreground app just prior to source sharing app. Share often occurs between
+     * two apps the user is switching.
+     */
+    private static void promoteForegroundApp(
+            Map<String, List<ShareTargetPredictor.ShareTarget>> shareTargetMap,
+            @NonNull DataManager dataManager, @UserIdInt int callingUserId) {
+        String sharingForegroundApp = findSharingForegroundApp(shareTargetMap, dataManager,
+                callingUserId);
+        if (sharingForegroundApp != null) {
+            ShareTargetPredictor.ShareTarget target = shareTargetMap.get(sharingForegroundApp).get(
+                    0);
+            target.setScore(probOR(target.getScore(), FOREGROUND_APP_WEIGHT));
+            if (DEBUG) {
+                Slog.d(TAG, String.format(
+                        "SharesheetModel: promoteForegroundApp packageName: %s, className: %s, "
+                                + "total:%.2f",
+                        target.getAppTarget().getPackageName(),
+                        target.getAppTarget().getClassName(),
+                        target.getScore()));
+            }
+        }
+    }
+
+    /**
+     * Find the foreground app just prior to source sharing app from usageStatsManager. Returns null
+     * if it is not available.
+     */
+    @Nullable
+    private static String findSharingForegroundApp(
+            Map<String, List<ShareTargetPredictor.ShareTarget>> shareTargetMap,
+            @NonNull DataManager dataManager, @UserIdInt int callingUserId) {
+        String sharingForegroundApp = null;
+        long now = System.currentTimeMillis();
+        List<UsageEvents.Event> events = dataManager.queryAppMovingToForegroundEvents(
+                callingUserId, now - FOREGROUND_APP_PROMO_TIME_WINDOW, now);
+        String sourceApp = null;
+        for (int i = events.size() - 1; i >= 0; i--) {
+            String className = events.get(i).getClassName();
+            String packageName = events.get(i).getPackageName();
+            if (packageName == null || (className != null && className.contains(CHOOSER_ACTIVITY))
+                    || packageName.contains(CHOOSER_ACTIVITY)) {
+                continue;
+            }
+            if (sourceApp == null) {
+                sourceApp = packageName;
+            } else if (!packageName.equals(sourceApp) && shareTargetMap.containsKey(packageName)) {
+                sharingForegroundApp = packageName;
+                break;
+            }
+        }
+        return sharingForegroundApp;
+    }
+
+    /**
+     * Probabilistic OR (also known as the algebraic sum). If a <= 1 and b <= 1, the result will be
+     * <= 1.0.
+     */
+    private static float probOR(float a, float b) {
+        return 1f - (1f - a) * (1f - b);
+    }
+
+    /** Counts frequency of share targets. Decays frequency for old shares. */
+    private static float getFreqDecayedOnElapsedTime(long elapsedTimeMillis) {
+        Duration duration = Duration.ofMillis(elapsedTimeMillis);
+        if (duration.compareTo(Duration.ofDays(1)) <= 0) {
+            return 1.0f;
+        } else if (duration.compareTo(Duration.ofDays(3)) <= 0) {
+            return 0.9f;
+        } else if (duration.compareTo(Duration.ofDays(7)) <= 0) {
+            return 0.8f;
+        } else if (duration.compareTo(Duration.ofDays(14)) <= 0) {
+            return 0.7f;
+        } else {
+            return 0.6f;
+        }
+    }
+
+    /** Normalizes frequency score. */
+    private static float normalizeFreqScore(double freqRatio) {
+        if (freqRatio >= 2.5) {
+            return 0.2f;
+        } else if (freqRatio >= 1.5) {
+            return 0.15f;
+        } else if (freqRatio >= 1.0) {
+            return 0.1f;
+        } else if (freqRatio >= 0.75) {
+            return 0.05f;
+        } else {
+            return 0f;
+        }
+    }
+
+    /** Normalizes mimetype-specific frequency score. */
+    private static float normalizeMimeFreqScore(double freqRatio) {
+        if (freqRatio >= 2.0) {
+            return 0.2f;
+        } else if (freqRatio >= 1.2) {
+            return 0.15f;
+        } else if (freqRatio > 0.0) {
+            return 0.1f;
+        } else {
+            return 0f;
+        }
+    }
+
+    private static class ShareTargetRankingScore {
+
+        private float mRecencyScore = 0f;
+        private float mFrequencyScore = 0f;
+        private float mMimeFrequencyScore = 0f;
+        private float mTotalScore = 0f;
+
+        float getTotalScore() {
+            return mTotalScore;
+        }
+
+        void setTotalScore(float totalScore) {
+            mTotalScore = totalScore;
+        }
+
+        float getRecencyScore() {
+            return mRecencyScore;
+        }
+
+        void setRecencyScore(float recencyScore) {
+            mRecencyScore = recencyScore;
+        }
+
+        float getFrequencyScore() {
+            return mFrequencyScore;
+        }
+
+        void setFrequencyScore(float frequencyScore) {
+            mFrequencyScore = frequencyScore;
+        }
+
+        void incrementFrequencyScore(float incremental) {
+            mFrequencyScore += incremental;
+        }
+
+        float getMimeFrequencyScore() {
+            return mMimeFrequencyScore;
+        }
+
+        void setMimeFrequencyScore(float mimeFrequencyScore) {
+            mMimeFrequencyScore = mimeFrequencyScore;
+        }
+
+        void incrementMimeFrequencyScore(float incremental) {
+            mMimeFrequencyScore += incremental;
+        }
+    }
+}