Homescreen migration from a larger grid to a smaller grid.

Adding support for restoring from a larger device, if the grid size
difference is not more that 1.
During restore add all the items in the DB, and run a one-time migration
the next time launcher starts.

The migration strategy is defined in ShrinkWorkspaceTask.java which involves
resizing, moving and removing some items.

Change-Id: I6ee411f6db5bf0152b527e16146a88c56dec2d97

src/com/android/launcher3/LauncherAppState.java

@@ -17,7 +17,6 @@
 package com.android.launcher3;
 
 import android.app.SearchManager;
-import android.content.ComponentName;
 import android.content.Context;
 import android.content.Intent;
 import android.content.IntentFilter;
@@ -147,7 +146,7 @@ public class LauncherAppState {
         sLauncherProvider = new WeakReference<LauncherProvider>(provider);
     }
 
-    static LauncherProvider getLauncherProvider() {
+    public static LauncherProvider getLauncherProvider() {
         return sLauncherProvider.get();
     }
 

src/com/android/launcher3/LauncherAppWidgetProviderInfo.java

@@ -5,6 +5,7 @@ import android.appwidget.AppWidgetProviderInfo;
 import android.content.ComponentName;
 import android.content.Context;
 import android.content.pm.PackageManager;
+import android.graphics.Point;
 import android.graphics.drawable.Drawable;
 import android.os.Build;
 import android.os.Parcel;
@@ -110,4 +111,15 @@ public class LauncherAppWidgetProviderInfo extends AppWidgetProviderInfo {
             mMinSpanY = minResizeSpan[1];
         }
     }
+
+    public Point getMinSpans(InvariantDeviceProfile idp, Context context) {
+        // Calculate the spans corresponding to any one of the orientations as it should not change
+        // based on orientation.
+        // TODO: Use the max of both profiles
+        int[] minSpans = CellLayout.rectToCell(
+                idp.portraitProfile, context, minResizeWidth, minResizeHeight, null);
+        return new Point(
+                (resizeMode & RESIZE_HORIZONTAL) != 0 ? minSpans[0] : -1,
+                        (resizeMode & RESIZE_VERTICAL) != 0 ? minSpans[1] : -1);
+    }
  }

src/com/android/launcher3/LauncherBackupAgentHelper.java

@@ -24,6 +24,8 @@ import android.database.Cursor;
 import android.os.ParcelFileDescriptor;
 import android.util.Log;
 
+import com.android.launcher3.model.MigrateFromRestoreTask;
+
 import java.io.IOException;
 
 public class LauncherBackupAgentHelper extends BackupAgentHelper {
@@ -96,6 +98,13 @@ public class LauncherBackupAgentHelper extends BackupAgentHelper {
                 LauncherAppState.getLauncherProvider().updateFolderItemsRank();
             }
 
+            if (mHelper.shouldAttemptWorkspaceMigration()) {
+                MigrateFromRestoreTask.markForMigration(getApplicationContext(),
+                        (int) mHelper.migrationCompatibleProfileData.desktopCols,
+                        (int) mHelper.migrationCompatibleProfileData.desktopRows,
+                        mHelper.widgetSizes);
+            }
+
             LauncherAppState.getLauncherProvider().convertShortcutsToLauncherActivities();
         } else {
             if (VERBOSE) Log.v(TAG, "Nothing was restored, clearing DB");

src/com/android/launcher3/LauncherBackupHelper.java

@@ -32,6 +32,7 @@ import android.content.res.XmlResourceParser;
 import android.database.Cursor;
 import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
+import android.graphics.Point;
 import android.graphics.drawable.Drawable;
 import android.os.ParcelFileDescriptor;
 import android.text.TextUtils;
@@ -152,6 +153,9 @@ public class LauncherBackupHelper implements BackupHelper {
     private DeviceProfieData mDeviceProfileData;
     private InvariantDeviceProfile mIdp;
 
+    DeviceProfieData migrationCompatibleProfileData;
+    HashSet<String> widgetSizes = new HashSet<>();
+
     boolean restoreSuccessful;
     int restoredBackupVersion = 1;
 
@@ -288,9 +292,9 @@ public class LauncherBackupHelper implements BackupHelper {
             return true;
         }
 
-        boolean isHotsetCompatible = false;
+        boolean isHotseatCompatible = false;
         if (currentProfile.allappsRank >= oldProfile.hotseatCount) {
-            isHotsetCompatible = true;
+            isHotseatCompatible = true;
             mHotseatShift = 0;
         }
 
@@ -298,12 +302,28 @@ public class LauncherBackupHelper implements BackupHelper {
                 && ((currentProfile.hotseatCount - currentProfile.allappsRank) >=
                         (oldProfile.hotseatCount - oldProfile.allappsRank))) {
             // There is enough space on both sides of the hotseat.
-            isHotsetCompatible = true;
+            isHotseatCompatible = true;
             mHotseatShift = currentProfile.allappsRank - oldProfile.allappsRank;
         }
 
-        return isHotsetCompatible && (currentProfile.desktopCols >= oldProfile.desktopCols)
-                && (currentProfile.desktopRows >= oldProfile.desktopRows);
+        if (!isHotseatCompatible) {
+            return false;
+        }
+        if ((currentProfile.desktopCols >= oldProfile.desktopCols)
+                && (currentProfile.desktopRows >= oldProfile.desktopRows)) {
+            return true;
+        }
+
+        if ((oldProfile.desktopCols - currentProfile.desktopCols <= 1) &&
+                (oldProfile.desktopRows - currentProfile.desktopRows <= 1)) {
+            // Allow desktop migration when row and/or column count contracts by 1.
+
+            migrationCompatibleProfileData = initDeviceProfileData(mIdp);
+            migrationCompatibleProfileData.desktopCols = oldProfile.desktopCols;
+            migrationCompatibleProfileData.desktopRows = oldProfile.desktopRows;
+            return true;
+        }
+        return false;
     }
 
     /**
@@ -706,7 +726,8 @@ public class LauncherBackupHelper implements BackupHelper {
             }
         }
 
-        // future site of widget table mutation
+        // Cache widget min sizes incase migration is required.
+        widgetSizes.add(widget.provider + "#" + widget.minSpanX + "," + widget.minSpanY);
     }
 
     /** create a new key, with an integer ID.
@@ -904,7 +925,11 @@ public class LauncherBackupHelper implements BackupHelper {
                 UserManagerCompat.getInstance(mContext).getSerialNumberForUser(myUserHandle);
         values.put(LauncherSettings.Favorites.PROFILE_ID, userSerialNumber);
 
-        DeviceProfieData currentProfile = mDeviceProfileData;
+        // If we will attempt grid resize, use the original profile to validate grid size, as
+        // anything which fits in the original grid should fit in the current grid after
+        // grid migration.
+        DeviceProfieData currentProfile = migrationCompatibleProfileData == null
+                ? mDeviceProfileData : migrationCompatibleProfileData;
 
         if (favorite.itemType == Favorites.ITEM_TYPE_APPWIDGET) {
             if (!TextUtils.isEmpty(favorite.appWidgetProvider)) {
@@ -996,14 +1021,9 @@ public class LauncherBackupHelper implements BackupHelper {
             widget.icon.dpi = dpi;
         }
 
-        // Calculate the spans corresponding to any one of the orientations as it should not change
-        // based on orientation.
-        int[] minSpans = CellLayout.rectToCell(
-                mIdp.portraitProfile, mContext, info.minResizeWidth, info.minResizeHeight, null);
-        widget.minSpanX = (info.resizeMode & LauncherAppWidgetProviderInfo.RESIZE_HORIZONTAL) != 0
-                ? minSpans[0] : -1;
-        widget.minSpanY = (info.resizeMode & LauncherAppWidgetProviderInfo.RESIZE_VERTICAL) != 0
-                ? minSpans[1] : -1;
+        Point spans = info.getMinSpans(mIdp, mContext);
+        widget.minSpanX = spans.x;
+        widget.minSpanY = spans.y;
 
         return widget;
     }
@@ -1188,6 +1208,10 @@ public class LauncherBackupHelper implements BackupHelper {
         }
     }
 
+    public boolean shouldAttemptWorkspaceMigration() {
+        return migrationCompatibleProfileData != null;
+    }
+
     /**
      * A class to check if an activity can handle one of the intents from a list of
      * predefined intents.

src/com/android/launcher3/LauncherModel.java

@@ -27,6 +27,7 @@ import android.content.Context;
 import android.content.Intent;
 import android.content.Intent.ShortcutIconResource;
 import android.content.IntentFilter;
+import android.content.SharedPreferences;
 import android.content.pm.PackageManager;
 import android.content.pm.ProviderInfo;
 import android.content.pm.ResolveInfo;
@@ -55,6 +56,7 @@ import com.android.launcher3.compat.PackageInstallerCompat;
 import com.android.launcher3.compat.PackageInstallerCompat.PackageInstallInfo;
 import com.android.launcher3.compat.UserHandleCompat;
 import com.android.launcher3.compat.UserManagerCompat;
+import com.android.launcher3.model.MigrateFromRestoreTask;
 import com.android.launcher3.model.WidgetsModel;
 import com.android.launcher3.util.ComponentKey;
 import com.android.launcher3.util.CursorIconInfo;
@@ -1133,7 +1135,7 @@ public class LauncherModel extends BroadcastReceiver
      * Update the order of the workspace screens in the database. The array list contains
      * a list of screen ids in the order that they should appear.
      */
-    void updateWorkspaceScreenOrder(Context context, final ArrayList<Long> screens) {
+    public void updateWorkspaceScreenOrder(Context context, final ArrayList<Long> screens) {
         final ArrayList<Long> screensCopy = new ArrayList<Long>(screens);
         final ContentResolver cr = context.getContentResolver();
         final Uri uri = LauncherSettings.WorkspaceScreens.CONTENT_URI;
@@ -1411,7 +1413,7 @@ public class LauncherModel extends BroadcastReceiver
     /**
      * Loads the workspace screen ids in an ordered list.
      */
-    @Thunk static ArrayList<Long> loadWorkspaceScreensDb(Context context) {
+    public static ArrayList<Long> loadWorkspaceScreensDb(Context context) {
         final ContentResolver contentResolver = context.getContentResolver();
         final Uri screensUri = LauncherSettings.WorkspaceScreens.CONTENT_URI;
 
@@ -1757,6 +1759,22 @@ public class LauncherModel extends BroadcastReceiver
             int countX = (int) profile.numColumns;
             int countY = (int) profile.numRows;
 
+
+            if (MigrateFromRestoreTask.shouldRunTask(mContext)) {
+                try {
+                    MigrateFromRestoreTask task = new MigrateFromRestoreTask(mContext);
+                    // Clear the flags before starting the task, so that we do not run the task
+                    // again, in case there was an uncaught error.
+                    MigrateFromRestoreTask.clearFlags(mContext);
+                    task.execute();
+                } catch (Exception e) {
+                    Log.e(TAG, "Error during grid migration", e);
+
+                    // Clear workspace.
+                    mFlags = mFlags | LOADER_FLAG_CLEAR_WORKSPACE;
+                }
+            }
+
             if ((mFlags & LOADER_FLAG_CLEAR_WORKSPACE) != 0) {
                 Launcher.addDumpLog(TAG, "loadWorkspace: resetting launcher database", true);
                 LauncherAppState.getLauncherProvider().deleteDatabase();

src/com/android/launcher3/LauncherProvider.java

@@ -71,7 +71,7 @@ public class LauncherProvider extends ContentProvider {
     private static final int DATABASE_VERSION = 26;
 
     static final String OLD_AUTHORITY = "com.android.launcher2.settings";
-    static final String AUTHORITY = ProviderConfig.AUTHORITY;
+    public static final String AUTHORITY = ProviderConfig.AUTHORITY;
 
     static final String TABLE_FAVORITES = LauncherSettings.Favorites.TABLE_NAME;
     static final String TABLE_WORKSPACE_SCREENS = LauncherSettings.WorkspaceScreens.TABLE_NAME;

src/com/android/launcher3/LauncherSettings.java

@@ -143,7 +143,7 @@ public class LauncherSettings {
          *
          * @return The unique content URL for the specified row.
          */
-        static Uri getContentUri(long id) {
+        public static Uri getContentUri(long id) {
             return Uri.parse("content://" + ProviderConfig.AUTHORITY +
                     "/" + TABLE_NAME + "/" + id);
         }

src/com/android/launcher3/model/MigrateFromRestoreTask.java

@@ -0,0 +1,765 @@
+package com.android.launcher3.model;
+
+import android.content.ComponentName;
+import android.content.ContentProviderOperation;
+import android.content.ContentValues;
+import android.content.Context;
+import android.content.Intent;
+import android.content.SharedPreferences;
+import android.content.pm.PackageInfo;
+import android.database.Cursor;
+import android.graphics.Point;
+import android.text.TextUtils;
+import android.util.Log;
+
+import com.android.launcher3.InvariantDeviceProfile;
+import com.android.launcher3.ItemInfo;
+import com.android.launcher3.LauncherAppState;
+import com.android.launcher3.LauncherAppWidgetProviderInfo;
+import com.android.launcher3.LauncherModel;
+import com.android.launcher3.LauncherProvider;
+import com.android.launcher3.LauncherSettings;
+import com.android.launcher3.LauncherSettings.Favorites;
+import com.android.launcher3.Utilities;
+import com.android.launcher3.compat.PackageInstallerCompat;
+import com.android.launcher3.compat.UserHandleCompat;
+import com.android.launcher3.util.LongArrayMap;
+import com.android.launcher3.util.Thunk;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+
+/**
+ * This class takes care of shrinking the workspace (by maximum of one row and one column), as a
+ * result of restoring from a larger device.
+ */
+public class MigrateFromRestoreTask {
+
+    private static final String TAG = "MigrateFromRestoreTask";
+    private static final boolean DEBUG = false;
+
+    private static final String KEY_MIGRATION_SOURCE_SIZE = "migration_restore_src_size";
+    private static final String KEY_MIGRATION_WIDGET_MINSIZE = "migration_widget_min_size";
+
+    // These are carefully selected weights for various item types (Math.random?), to allow for
+    // the lease absurd migration experience.
+    private static final float WT_SHORTCUT = 1;
+    private static final float WT_APPLICATION = 0.8f;
+    private static final float WT_WIDGET_MIN = 2;
+    private static final float WT_WIDGET_FACTOR = 0.6f;
+    private static final float WT_FOLDER_FACTOR = 0.5f;
+
+    private final Context mContext;
+    private final ContentValues mTempValues = new ContentValues();
+    private final HashMap<String, Point> mWidgetMinSize;
+    private final InvariantDeviceProfile mIdp;
+
+    private HashSet<String> mValidPackages;
+    public ArrayList<Long> mEntryToRemove;
+    private ArrayList<ContentProviderOperation> mUpdateOperations;
+
+    private ArrayList<DbEntry> mCarryOver;
+
+    private final int mSrcX, mSrcY;
+    @Thunk final int mTrgX, mTrgY;
+    private final boolean mShouldRemoveX, mShouldRemoveY;
+
+    public MigrateFromRestoreTask(Context context) {
+        mContext = context;
+
+        SharedPreferences prefs = prefs(context);
+        Point sourceSize = parsePoint(prefs.getString(KEY_MIGRATION_SOURCE_SIZE, ""));
+        mSrcX = sourceSize.x;
+        mSrcY = sourceSize.y;
+
+        mWidgetMinSize = new HashMap<String, Point>();
+        for (String s : prefs.getStringSet(KEY_MIGRATION_WIDGET_MINSIZE,
+                Collections.<String>emptySet())) {
+            String[] parts = s.split("#");
+            mWidgetMinSize.put(parts[0], parsePoint(parts[1]));
+        }
+
+        mIdp = LauncherAppState.getInstance().getInvariantDeviceProfile();
+        mTrgX = mIdp.numColumns;
+        mTrgY = mIdp.numRows;
+        mShouldRemoveX = mTrgX < mSrcX;
+        mShouldRemoveY = mTrgY < mSrcY;
+    }
+
+    public void execute() throws Exception {
+        mEntryToRemove = new ArrayList<>();
+        mCarryOver = new ArrayList<>();
+        mUpdateOperations = new ArrayList<>();
+
+        // Initialize list of valid packages. This contain all the packages which are already on
+        // the device and packages which are being installed. Any item which doesn't belong to
+        // this set is removed.
+        // Since the loader removes such items anyway, removing these items here doesn't cause any
+        // extra data loss and gives us more free space on the grid for better migration.
+        mValidPackages = new HashSet<>();
+        for (PackageInfo info : mContext.getPackageManager().getInstalledPackages(0)) {
+            mValidPackages.add(info.packageName);
+        }
+        mValidPackages.addAll(PackageInstallerCompat.getInstance(mContext)
+                .updateAndGetActiveSessionCache().keySet());
+
+        ArrayList<Long> allScreens = LauncherModel.loadWorkspaceScreensDb(mContext);
+        if (allScreens.isEmpty()) {
+            throw new Exception("Unable to get workspace screens");
+        }
+
+        for (long screenId : allScreens) {
+            if (DEBUG) {
+                Log.d(TAG, "Migrating " + screenId);
+            }
+            migrateScreen(screenId);
+        }
+
+        if (!mCarryOver.isEmpty()) {
+            LongArrayMap<DbEntry> itemMap = new LongArrayMap<>();
+            for (DbEntry e : mCarryOver) {
+                itemMap.put(e.id, e);
+            }
+
+            do {
+                // Some items are still remaining. Try adding a few new screens.
+
+                // At every iteration, make sure that at least one item is removed from
+                // {@link #mCarryOver}, to prevent an infinite loop. If no item could be removed,
+                // break the loop and abort migration by throwing an exception.
+                OptimalPlacementSolution placement = new OptimalPlacementSolution(
+                        new boolean[mTrgX][mTrgY], deepCopy(mCarryOver), true);
+                placement.find();
+                if (placement.finalPlacedItems.size() > 0) {
+                    long newScreenId = LauncherAppState.getLauncherProvider().generateNewScreenId();
+                    allScreens.add(newScreenId);
+                    for (DbEntry item : placement.finalPlacedItems) {
+                        if (!mCarryOver.remove(itemMap.get(item.id))) {
+                            throw new Exception("Unable to find matching items");
+                        }
+                        item.screenId = newScreenId;
+                        update(item);
+                    }
+                } else {
+                    throw new Exception("None of the items can be placed on an empty screen");
+                }
+
+            } while (!mCarryOver.isEmpty());
+
+
+            LauncherAppState.getInstance().getModel()
+                .updateWorkspaceScreenOrder(mContext, allScreens);
+        }
+
+        // Update items
+        mContext.getContentResolver().applyBatch(LauncherProvider.AUTHORITY, mUpdateOperations);
+
+        if (!mEntryToRemove.isEmpty()) {
+            if (DEBUG) {
+                Log.d(TAG, "Removing items: " + TextUtils.join(", ", mEntryToRemove));
+            }
+            mContext.getContentResolver().delete(LauncherSettings.Favorites.CONTENT_URI,
+                    Utilities.createDbSelectionQuery(
+                            LauncherSettings.Favorites._ID, mEntryToRemove), null);
+        }
+
+        // Make sure we haven't removed everything.
+        final Cursor c = mContext.getContentResolver().query(
+                LauncherSettings.Favorites.CONTENT_URI, null, null, null, null);
+        boolean hasData = c.moveToNext();
+        c.close();
+        if (!hasData) {
+            throw new Exception("Removed every thing during grid resize");
+        }
+    }
+
+    /**
+     * Migrate a particular screen id.
+     * Strategy:
+     *   1) For all possible combinations of row and column, pick the one which causes the least
+     *      data loss: {@link #tryRemove(int, int, ArrayList, float[])}
+     *   2) Maintain a list of all lost items before this screen, and add any new item lost from
+     *      this screen to that list as well.
+     *   3) If all those items from the above list can be placed on this screen, place them
+     *      (otherwise they are placed on a new screen).
+     */
+    private void migrateScreen(long screenId) {
+        ArrayList<DbEntry> items = loadEntries(screenId);
+
+        int removedCol = Integer.MAX_VALUE;
+        int removedRow = Integer.MAX_VALUE;
+
+        // removeWt represents the cost function for loss of items during migration, and moveWt
+        // represents the cost function for repositioning the items. moveWt is only considered if
+        // removeWt is same for two different configurations.
+        // Start with Float.MAX_VALUE (assuming full data) and pick the configuration with least
+        // cost.
+        float removeWt = Float.MAX_VALUE;
+        float moveWt = Float.MAX_VALUE;
+        float[] outLoss = new float[2];
+        ArrayList<DbEntry> finalItems = null;
+
+        // Try removing all possible combinations
+        for (int x = 0; x < mSrcX; x++) {
+            for (int y = 0; y < mSrcY; y++) {
+                // Use a deep copy when trying out a particular combination as it can change
+                // the underlying object.
+                ArrayList<DbEntry> itemsOnScreen = tryRemove(x, y, deepCopy(items), outLoss);
+
+                if ((outLoss[0] < removeWt) || ((outLoss[0] == removeWt) && (outLoss[1] < moveWt))) {
+                    removeWt = outLoss[0];
+                    moveWt = outLoss[1];
+                    removedCol = mShouldRemoveX ? x : removedCol;
+                    removedRow = mShouldRemoveY ? y : removedRow;
+                    finalItems = itemsOnScreen;
+                }
+
+                // No need to loop over all rows, if a row removal is not needed.
+                if (!mShouldRemoveY) {
+                    break;
+                }
+            }
+
+            if (!mShouldRemoveX) {
+                break;
+            }
+        }
+
+        if (DEBUG) {
+            Log.d(TAG, String.format("Removing row %d, column %d on screen %d",
+                    removedRow, removedCol, screenId));
+        }
+
+        LongArrayMap<DbEntry> itemMap = new LongArrayMap<>();
+        for (DbEntry e : deepCopy(items)) {
+            itemMap.put(e.id, e);
+        }
+
+        for (DbEntry item : finalItems) {
+            DbEntry org = itemMap.get(item.id);
+            itemMap.remove(item.id);
+
+            // Check if update is required
+            if (!item.columnsSame(org)) {
+                update(item);
+            }
+        }
+
+        // The remaining items in {@link #itemMap} are those which didn't get placed.
+        for (DbEntry item : itemMap) {
+            mCarryOver.add(item);
+        }
+
+        if (!mCarryOver.isEmpty() && removeWt == 0) {
+            // No new items were removed in this step. Try placing all the items on this screen.
+            boolean[][] occupied = new boolean[mTrgX][mTrgY];
+            for (DbEntry item : finalItems) {
+                markCells(occupied, item, true);
+            }
+
+            OptimalPlacementSolution placement = new OptimalPlacementSolution(occupied,
+                    deepCopy(mCarryOver), true);
+            placement.find();
+            if (placement.lowestWeightLoss == 0) {
+                // All items got placed
+
+                for (DbEntry item : placement.finalPlacedItems) {
+                    item.screenId = screenId;
+                    update(item);
+                }
+
+                mCarryOver.clear();
+            }
+        }
+    }
+
+    /**
+     * Updates an item in the DB.
+     */
+    private void update(DbEntry item) {
+        mTempValues.clear();
+        item.addToContentValues(mTempValues);
+        mUpdateOperations.add(ContentProviderOperation
+                .newUpdate(LauncherSettings.Favorites.getContentUri(item.id))
+                .withValues(mTempValues).build());
+    }
+
+    /**
+     * Tries the remove the provided row and column.
+     * @param items all the items on the screen under operation
+     * @param outLoss array of size 2. The first entry is filled with weight loss, and the second
+     * with the overall item movement.
+     */
+    private ArrayList<DbEntry> tryRemove(int col, int row, ArrayList<DbEntry> items,
+            float[] outLoss) {
+        boolean[][] occupied = new boolean[mTrgX][mTrgY];
+
+        col = mShouldRemoveX ? col : Integer.MAX_VALUE;
+        row = mShouldRemoveY ? row : Integer.MAX_VALUE;
+
+        ArrayList<DbEntry> finalItems = new ArrayList<>();
+        ArrayList<DbEntry> removedItems = new ArrayList<>();
+
+        for (DbEntry item : items) {
+            if ((item.cellX <= col && (item.spanX + item.cellX) > col)
+                || (item.cellY <= row && (item.spanY + item.cellY) > row)) {
+                removedItems.add(item);
+                if (item.cellX >= col) item.cellX --;
+                if (item.cellY >= row) item.cellY --;
+            } else {
+                if (item.cellX > col) item.cellX --;
+                if (item.cellY > row) item.cellY --;
+                finalItems.add(item);
+                markCells(occupied, item, true);
+            }
+        }
+
+        OptimalPlacementSolution placement = new OptimalPlacementSolution(occupied, removedItems);
+        placement.find();
+        finalItems.addAll(placement.finalPlacedItems);
+        outLoss[0] = placement.lowestWeightLoss;
+        outLoss[1] = placement.lowestMoveCost;
+        return finalItems;
+    }
+
+    @Thunk void markCells(boolean[][] occupied, DbEntry item, boolean val) {
+        for (int i = item.cellX; i < (item.cellX + item.spanX); i++) {
+            for (int j = item.cellY; j < (item.cellY + item.spanY); j++) {
+                occupied[i][j] = val;
+            }
+        }
+    }
+
+    @Thunk boolean isVacant(boolean[][] occupied, int x, int y, int w, int h) {
+        if (x + w > mTrgX) return false;
+        if (y + h > mTrgY) return false;
+
+        for (int i = 0; i < w; i++) {
+            for (int j = 0; j < h; j++) {
+                if (occupied[i + x][j + y]) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    private class OptimalPlacementSolution {
+        private final ArrayList<DbEntry> itemsToPlace;
+        private final boolean[][] occupied;
+
+        // If set to true, item movement are not considered in move cost, leading to a more
+        // linear placement.
+        private final boolean ignoreMove;
+
+        float lowestWeightLoss = Float.MAX_VALUE;
+        float lowestMoveCost = Float.MAX_VALUE;
+        ArrayList<DbEntry> finalPlacedItems;
+
+        public OptimalPlacementSolution(boolean[][] occupied, ArrayList<DbEntry> itemsToPlace) {
+            this(occupied, itemsToPlace, false);
+        }
+
+        public OptimalPlacementSolution(boolean[][] occupied, ArrayList<DbEntry> itemsToPlace,
+                boolean ignoreMove) {
+            this.occupied = occupied;
+            this.itemsToPlace = itemsToPlace;
+            this.ignoreMove = ignoreMove;
+
+            // Sort the items such that larger widgets appear first followed by 1x1 items
+            Collections.sort(this.itemsToPlace);
+        }
+
+        public void find() {
+            find(0, 0, 0, new ArrayList<DbEntry>());
+        }
+
+        /**
+         * Recursively finds a placement for the provided items.
+         * @param index the position in {@link #itemsToPlace} to start looking at.
+         * @param weightLoss total weight loss upto this point
+         * @param moveCost total move cost upto this point
+         * @param itemsPlaced all the items already placed upto this point
+         */
+        public void find(int index, float weightLoss, float moveCost,
+                ArrayList<DbEntry> itemsPlaced) {
+            if ((weightLoss >= lowestWeightLoss) ||
+                    ((weightLoss == lowestWeightLoss) && (moveCost >= lowestMoveCost))) {
+                // Abort, as we already have a better solution.
+                return;
+
+            } else if (index >= itemsToPlace.size()) {
+                // End loop.
+                lowestWeightLoss = weightLoss;
+                lowestMoveCost = moveCost;
+
+                // Keep a deep copy of current configuration as it can change during recursion.
+                finalPlacedItems = deepCopy(itemsPlaced);
+                return;
+            }
+
+            DbEntry me = itemsToPlace.get(index);
+            int myX = me.cellX;
+            int myY = me.cellY;
+
+            // List of items to pass over if this item was placed.
+            ArrayList<DbEntry> itemsIncludingMe = new ArrayList<>(itemsPlaced.size() + 1);
+            itemsIncludingMe.addAll(itemsPlaced);
+            itemsIncludingMe.add(me);
+
+            if (me.spanX > 1 || me.spanY > 1) {
+                // If the current item is a widget (and it greater than 1x1), try to place it at
+                // all possible positions. This is because a widget placed at one position can
+                // affect the placement of a different widget.
+                int myW = me.spanX;
+                int myH = me.spanY;
+
+                for (int y = 0; y < mTrgY; y++) {
+                    for (int x = 0; x < mTrgX; x++) {
+                        float newMoveCost = moveCost;
+                        if (x != myX) {
+                            me.cellX = x;
+                            newMoveCost ++;
+                        }
+                        if (y != myY) {
+                            me.cellY = y;
+                            newMoveCost ++;
+                        }
+                        if (ignoreMove) {
+                            newMoveCost = moveCost;
+                        }
+
+                        if (isVacant(occupied, x, y, myW, myH)) {
+                            // place at this position and continue search.
+                            markCells(occupied, me, true);
+                            find(index + 1, weightLoss, newMoveCost, itemsIncludingMe);
+                            markCells(occupied, me, false);
+                        }
+
+                        // Try resizing horizontally
+                        if (myW > me.minSpanX && isVacant(occupied, x, y, myW - 1, myH)) {
+                            me.spanX --;
+                            markCells(occupied, me, true);
+                            // 1 extra move cost
+                            find(index + 1, weightLoss, newMoveCost + 1, itemsIncludingMe);
+                            markCells(occupied, me, false);
+                            me.spanX ++;
+                        }
+
+                        // Try resizing vertically
+                        if (myH > me.minSpanY && isVacant(occupied, x, y, myW, myH - 1)) {
+                            me.spanY --;
+                            markCells(occupied, me, true);
+                            // 1 extra move cost
+                            find(index + 1, weightLoss, newMoveCost + 1, itemsIncludingMe);
+                            markCells(occupied, me, false);
+                            me.spanY ++;
+                        }
+
+                        // Try resizing horizontally & vertically
+                        if (myH > me.minSpanY && myW > me.minSpanX &&
+                                isVacant(occupied, x, y, myW - 1, myH - 1)) {
+                            me.spanX --;
+                            me.spanY --;
+                            markCells(occupied, me, true);
+                            // 2 extra move cost
+                            find(index + 1, weightLoss, newMoveCost + 2, itemsIncludingMe);
+                            markCells(occupied, me, false);
+                            me.spanX ++;
+                            me.spanY ++;
+                        }
+                        me.cellX = myX;
+                        me.cellY = myY;
+                    }
+                }
+
+                // Finally also try a solution when this item is not included. Trying it in the end
+                // causes it to get skipped in most cases due to higher weight loss, and prevents
+                // unnecessary deep copies of various configurations.
+                find(index + 1, weightLoss + me.weight, moveCost, itemsPlaced);
+            } else {
+                // Since this is a 1x1 item and all the following items are also 1x1, just place
+                // it at 'the most appropriate position' and hope for the best.
+                // The most appropriate position: one with lease straight line distance
+                int newDistance = Integer.MAX_VALUE;
+                int newX = Integer.MAX_VALUE, newY = Integer.MAX_VALUE;
+
+                for (int y = 0; y < mTrgY; y++) {
+                    for (int x = 0; x < mTrgX; x++) {
+                        if (!occupied[x][y]) {
+                            int dist = ignoreMove ? 0 :
+                                ((me.cellX - x) * (me.cellX - x) + (me.cellY - y) * (me.cellY - y));
+                            if (dist < newDistance) {
+                                newX = x;
+                                newY = y;
+                                newDistance = dist;
+                            }
+                        }
+                    }
+                }
+
+                if (newX < mTrgX && newY < mTrgY) {
+                    float newMoveCost = moveCost;
+                    if (newX != myX) {
+                        me.cellX = newX;
+                        newMoveCost ++;
+                    }
+                    if (newY != myY) {
+                        me.cellY = newY;
+                        newMoveCost ++;
+                    }
+                    if (ignoreMove) {
+                        newMoveCost = moveCost;
+                    }
+                    markCells(occupied, me, true);
+                    find(index + 1, weightLoss, newMoveCost, itemsIncludingMe);
+                    markCells(occupied, me, false);
+                    me.cellX = myX;
+                    me.cellY = myY;
+
+                    // Try to find a solution without this item, only if
+                    //  1) there was at least one space, i.e., we were able to place this item
+                    //  2) if the next item has the same weight (all items are already sorted), as
+                    //     if it has lower weight, that solution will automatically get discarded.
+                    //  3) ignoreMove false otherwise, move cost is ignored and the weight will
+                    //      anyway be same.
+                    if (index + 1 < itemsToPlace.size()
+                            && itemsToPlace.get(index + 1).weight >= me.weight && !ignoreMove) {
+                        find(index + 1, weightLoss + me.weight, moveCost, itemsPlaced);
+                    }
+                } else {
+                    // No more space. Jump to the end.
+                    for (int i = index + 1; i < itemsToPlace.size(); i++) {
+                        weightLoss += itemsToPlace.get(i).weight;
+                    }
+                    find(itemsToPlace.size(), weightLoss + me.weight, moveCost, itemsPlaced);
+                }
+            }
+        }
+    }
+
+    /**
+     * Loads entries for a particular screen id.
+     */
+    public ArrayList<DbEntry> loadEntries(long screen) {
+       Cursor c =  mContext.getContentResolver().query(LauncherSettings.Favorites.CONTENT_URI,
+                new String[] {
+                    Favorites._ID,                  // 0
+                    Favorites.ITEM_TYPE,            // 1
+                    Favorites.CELLX,                // 2
+                    Favorites.CELLY,                // 3
+                    Favorites.SPANX,                // 4
+                    Favorites.SPANY,                // 5
+                    Favorites.INTENT,               // 6
+                    Favorites.APPWIDGET_PROVIDER},  // 7
+                Favorites.CONTAINER + " = " + Favorites.CONTAINER_DESKTOP
+                    + " AND " + Favorites.SCREEN + " = " + screen, null, null, null);
+
+       final int indexId = c.getColumnIndexOrThrow(Favorites._ID);
+       final int indexItemType = c.getColumnIndexOrThrow(Favorites.ITEM_TYPE);
+       final int indexCellX = c.getColumnIndexOrThrow(Favorites.CELLX);
+       final int indexCellY = c.getColumnIndexOrThrow(Favorites.CELLY);
+       final int indexSpanX = c.getColumnIndexOrThrow(Favorites.SPANX);
+       final int indexSpanY = c.getColumnIndexOrThrow(Favorites.SPANY);
+       final int indexIntent = c.getColumnIndexOrThrow(Favorites.INTENT);
+       final int indexAppWidgetProvider = c.getColumnIndexOrThrow(Favorites.APPWIDGET_PROVIDER);
+
+       ArrayList<DbEntry> entries = new ArrayList<>();
+       while (c.moveToNext()) {
+           DbEntry entry = new DbEntry();
+           entry.id = c.getLong(indexId);
+           entry.itemType = c.getInt(indexItemType);
+           entry.cellX = c.getInt(indexCellX);
+           entry.cellY = c.getInt(indexCellY);
+           entry.spanX = c.getInt(indexSpanX);
+           entry.spanY = c.getInt(indexSpanY);
+           entry.screenId = screen;
+
+           try {
+               // calculate weight
+               switch (entry.itemType) {
+                   case Favorites.ITEM_TYPE_SHORTCUT:
+                   case Favorites.ITEM_TYPE_APPLICATION: {
+                       verifyIntent(c.getString(indexIntent));
+                       entry.weight = entry.itemType == Favorites.ITEM_TYPE_SHORTCUT
+                           ? WT_SHORTCUT : WT_APPLICATION;
+                       break;
+                   }
+                   case Favorites.ITEM_TYPE_APPWIDGET: {
+                       String provider = c.getString(indexAppWidgetProvider);
+                       ComponentName cn = ComponentName.unflattenFromString(provider);
+                       verifyPackage(cn.getPackageName());
+                       entry.weight = Math.max(WT_WIDGET_MIN, WT_WIDGET_FACTOR
+                               * entry.spanX * entry.spanY);
+
+                       // Migration happens for current user only.
+                       LauncherAppWidgetProviderInfo pInfo = LauncherModel.getProviderInfo(
+                               mContext, cn, UserHandleCompat.myUserHandle());
+                       Point spans = pInfo == null ?
+                               mWidgetMinSize.get(provider) : pInfo.getMinSpans(mIdp, mContext);
+                       if (spans != null) {
+                           entry.minSpanX = spans.x > 0 ? spans.x : entry.spanX;
+                           entry.minSpanY = spans.y > 0 ? spans.y : entry.spanY;
+                       } else {
+                           // Assume that the widget be resized down to 2x2
+                           entry.minSpanX = entry.minSpanY = 2;
+                       }
+
+                       if (entry.minSpanX > mTrgX || entry.minSpanY > mTrgY) {
+                           throw new Exception("Widget can't be resized down to fit the grid");
+                       }
+                       break;
+                   }
+                   case Favorites.ITEM_TYPE_FOLDER: {
+                       int total = getFolderItemsCount(entry.id);
+                       if (total == 0) {
+                           throw new Exception("Folder is empty");
+                       }
+                       entry.weight = WT_FOLDER_FACTOR * total;
+                       break;
+                   }
+                   default:
+                       throw new Exception("Invalid item type");
+               }
+           } catch (Exception e) {
+               if (DEBUG) {
+                   Log.d(TAG, "Removing item " + entry.id, e);
+               }
+               mEntryToRemove.add(entry.id);
+               continue;
+           }
+
+           entries.add(entry);
+       }
+       return entries;
+    }
+
+    /**
+     * @return the number of valid items in the folder.
+     */
+    private int getFolderItemsCount(long folderId) {
+        Cursor c =  mContext.getContentResolver().query(LauncherSettings.Favorites.CONTENT_URI,
+                new String[] {Favorites._ID, Favorites.INTENT},
+                Favorites.CONTAINER + " = " + folderId, null, null, null);
+
+        int total = 0;
+        while (c.moveToNext()) {
+            try {
+                verifyIntent(c.getString(1));
+                total++;
+            } catch (Exception e) {
+                mEntryToRemove.add(c.getLong(0));
+            }
+        }
+
+        return total;
+    }
+
+    /**
+     * Verifies if the intent should be restored.
+     */
+    private void verifyIntent(String intentStr) throws Exception {
+        Intent intent = Intent.parseUri(intentStr, 0);
+        if (intent.getComponent() != null) {
+            verifyPackage(intent.getComponent().getPackageName());
+        } else if (intent.getPackage() != null) {
+            // Only verify package if the component was null.
+            verifyPackage(intent.getPackage());
+        }
+    }
+
+    /**
+     * Verifies if the package should be restored
+     */
+    private void verifyPackage(String packageName) throws Exception {
+        if (!mValidPackages.contains(packageName)) {
+            throw new Exception("Package not available");
+        }
+    }
+
+    private static class DbEntry extends ItemInfo implements Comparable<DbEntry> {
+
+        public float weight;
+
+        public DbEntry() { }
+
+        public DbEntry copy() {
+            DbEntry entry = new DbEntry();
+            entry.copyFrom(this);
+            entry.weight = weight;
+            entry.minSpanX = minSpanX;
+            entry.minSpanY = minSpanY;
+            return entry;
+        }
+
+        /**
+         * Comparator such that larger widgets come first,  followed by all 1x1 items
+         * based on their weights.
+         */
+        @Override
+        public int compareTo(DbEntry another) {
+            if (itemType == Favorites.ITEM_TYPE_APPWIDGET) {
+                if (another.itemType == Favorites.ITEM_TYPE_APPWIDGET) {
+                    return another.spanY * another.spanX - spanX * spanY;
+                } else {
+                    return -1;
+                }
+            } else if (another.itemType == Favorites.ITEM_TYPE_APPWIDGET) {
+                return 1;
+            } else {
+                // Place higher weight before lower weight.
+                return Float.compare(another.weight, weight);
+            }
+        }
+
+        public boolean columnsSame(DbEntry org) {
+            return org.cellX == cellX && org.cellY == cellY && org.spanX == spanX &&
+                    org.spanY == spanY && org.screenId == screenId;
+        }
+
+        public void addToContentValues(ContentValues values) {
+            values.put(LauncherSettings.Favorites.SCREEN, screenId);
+            values.put(LauncherSettings.Favorites.CELLX, cellX);
+            values.put(LauncherSettings.Favorites.CELLY, cellY);
+            values.put(LauncherSettings.Favorites.SPANX, spanX);
+            values.put(LauncherSettings.Favorites.SPANY, spanY);
+        }
+    }
+
+    @Thunk static ArrayList<DbEntry> deepCopy(ArrayList<DbEntry> src) {
+        ArrayList<DbEntry> dup = new ArrayList<DbEntry>(src.size());
+        for (DbEntry e : src) {
+            dup.add(e.copy());
+        }
+        return dup;
+    }
+
+    private static Point parsePoint(String point) {
+        String[] split = point.split(",");
+        return new Point(Integer.parseInt(split[0]), Integer.parseInt(split[1]));
+    }
+
+    public static void markForMigration(Context context, int srcX, int srcY,
+            HashSet<String> widgets) {
+        prefs(context).edit()
+                .putString(KEY_MIGRATION_SOURCE_SIZE, srcX + "," + srcY)
+                .putStringSet(KEY_MIGRATION_WIDGET_MINSIZE, widgets)
+                .apply();
+    }
+
+    public static boolean shouldRunTask(Context context) {
+        return !TextUtils.isEmpty(prefs(context).getString(KEY_MIGRATION_SOURCE_SIZE, ""));
+    }
+
+    public static void clearFlags(Context context) {
+        prefs(context).edit().remove(KEY_MIGRATION_SOURCE_SIZE)
+                .remove(KEY_MIGRATION_WIDGET_MINSIZE).commit();
+    }
+
+    private static SharedPreferences prefs(Context context) {
+        return context.getSharedPreferences(LauncherAppState.getSharedPreferencesKey(),
+                Context.MODE_PRIVATE);
+    }
+}