Caching last predictions and loading it with model

Adding support for persisting itemInfos on disk. This uses
a separate xml file. Unlike prefs, it does not keep the items
in memory and is just a wraper over reading/writing a file.

Bug: 160748731
Change-Id: Iaccab9928ab8f30127fb3c2d630ca8ca83f0bd05

src/com/android/launcher3/util/PersistedItemArray.java

@@ -0,0 +1,180 @@
+/*
+ * 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.launcher3.util;
+
+import android.content.Context;
+import android.content.Intent;
+import android.os.UserHandle;
+import android.util.AtomicFile;
+import android.util.Log;
+import android.util.Xml;
+
+import androidx.annotation.Nullable;
+import androidx.annotation.WorkerThread;
+
+import com.android.launcher3.AutoInstallsLayout;
+import com.android.launcher3.LauncherSettings.Favorites;
+import com.android.launcher3.model.data.ItemInfo;
+import com.android.launcher3.pm.UserCache;
+
+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.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.function.LongFunction;
+
+/**
+ * Utility class to read/write a list of {@link com.android.launcher3.model.data.ItemInfo} on disk.
+ * This class is not thread safe, the caller should ensure proper threading
+ */
+public class PersistedItemArray<T extends ItemInfo> {
+
+    private static final String TAG = "PersistedItemArray";
+
+    private static final String TAG_ROOT = "items";
+    private static final String TAG_ENTRY = "entry";
+
+    private final String mFileName;
+
+    public PersistedItemArray(String fileName) {
+        mFileName = fileName + ".xml";
+    }
+
+    /**
+     * Writes the provided list of items on the disk
+     */
+    @WorkerThread
+    public void write(Context context, List<T> items) {
+        AtomicFile file = new AtomicFile(context.getFileStreamPath(mFileName));
+
+        FileOutputStream fos;
+        try {
+            fos = file.startWrite();
+        } catch (IOException e) {
+            Log.e(TAG, "Unable to persist items in " + mFileName, e);
+            return;
+        }
+
+        UserCache userCache = UserCache.INSTANCE.get(context);
+
+        try {
+            XmlSerializer out = Xml.newSerializer();
+            out.setOutput(fos, StandardCharsets.UTF_8.name());
+            out.startDocument(null, true);
+            out.startTag(null, TAG_ROOT);
+            for (T item : items) {
+                Intent intent = item.getIntent();
+                if (intent == null) {
+                    continue;
+                }
+
+                out.startTag(null, TAG_ENTRY);
+                out.attribute(null, Favorites.ITEM_TYPE, Integer.toString(item.itemType));
+                out.attribute(null, Favorites.PROFILE_ID,
+                        Long.toString(userCache.getSerialNumberForUser(item.user)));
+                out.attribute(null, Favorites.INTENT, intent.toUri(0));
+                out.endTag(null, TAG_ENTRY);
+            }
+            out.endTag(null, TAG_ROOT);
+            out.endDocument();
+        } catch (IOException e) {
+            file.failWrite(fos);
+            Log.e(TAG, "Unable to persist items in " + mFileName, e);
+            return;
+        }
+
+        file.finishWrite(fos);
+    }
+
+    /**
+     * Reads the items from the disk
+     */
+    @WorkerThread
+    public List<T> read(Context context, ItemFactory<T> factory) {
+        return read(context, factory, UserCache.INSTANCE.get(context)::getUserForSerialNumber);
+    }
+
+    /**
+     * Reads the items from the disk
+     * @param userFn method to provide user handle for a given user serial
+     */
+    @WorkerThread
+    public List<T> read(Context context, ItemFactory<T> factory, LongFunction<UserHandle> userFn) {
+        List<T> result = new ArrayList<>();
+        AtomicFile file = new AtomicFile(context.getFileStreamPath(mFileName));
+
+        try (FileInputStream fis = file.openRead()) {
+            XmlPullParser parser = Xml.newPullParser();
+            parser.setInput(new InputStreamReader(fis, StandardCharsets.UTF_8));
+
+            AutoInstallsLayout.beginDocument(parser, TAG_ROOT);
+            final int depth = parser.getDepth();
+
+            int type;
+            while (((type = parser.next()) != XmlPullParser.END_TAG
+                    || parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) {
+                if (type != XmlPullParser.START_TAG || !TAG_ENTRY.equals(parser.getName())) {
+                    continue;
+                }
+                try {
+                    int itemType = Integer.parseInt(
+                            parser.getAttributeValue(null, Favorites.ITEM_TYPE));
+                    UserHandle user = userFn.apply(Long.parseLong(
+                            parser.getAttributeValue(null, Favorites.PROFILE_ID)));
+                    Intent intent = Intent.parseUri(
+                            parser.getAttributeValue(null, Favorites.INTENT), 0);
+
+                    if (user != null && intent != null) {
+                        T item = factory.createInfo(itemType, user, intent);
+                        if (item != null) {
+                            result.add(item);
+                        }
+                    }
+                } catch (Exception e) {
+                    // Ignore this entry
+                }
+            }
+        } catch (FileNotFoundException e) {
+            // Ignore
+        } catch (IOException | XmlPullParserException e) {
+            Log.e(TAG, "Unable to read items in " + mFileName, e);
+            return Collections.emptyList();
+        }
+        return result;
+    }
+
+    /**
+     * Interface to create an ItemInfo during parsing
+     */
+    public interface ItemFactory<T extends ItemInfo> {
+
+        /**
+         * Returns an item info or null in which case the entry is ignored
+         */
+        @Nullable
+        T createInfo(int itemType, UserHandle user, Intent intent);
+    }
+}