1 files changed, 108 insertions, 0 deletions
diff --git a/src/com/android/launcher3/model/DbDowngradeHelper.java b/src/com/android/launcher3/model/DbDowngradeHelper.java
new file mode 100644
index 000000000..cd86b728b
--- /dev/null
+++ b/src/com/android/launcher3/model/DbDowngradeHelper.java
@@ -0,0 +1,108 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.android.launcher3.model;
+
+import android.content.Context;
+import android.database.sqlite.SQLiteDatabase;
+import android.database.sqlite.SQLiteException;
+import android.util.Log;
+import android.util.SparseArray;
+
+import com.android.launcher3.provider.LauncherDbUtils.SQLiteTransaction;
+import com.android.launcher3.util.IOUtils;
+
+import org.json.JSONArray;
+import org.json.JSONException;
+import org.json.JSONObject;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.ArrayList;
+import java.util.Collections;
+
+/**
+ * Utility class to handle DB downgrade
+ */
+public class DbDowngradeHelper {
+
+    private static final String TAG = "DbDowngradeHelper";
+
+    private static final String KEY_VERSION = "version";
+    private static final String KEY_DOWNGRADE_TO = "downgrade_to_";
+
+    private final SparseArray<String[]> mStatements = new SparseArray<>();
+    public final int version;
+
+    private DbDowngradeHelper(int version) {
+        this.version = version;
+    }
+
+    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
+        ArrayList<String> allCommands = new ArrayList<>();
+
+        for (int i = oldVersion - 1; i >= newVersion; i--) {
+            String[] commands = mStatements.get(i);
+            if (commands == null) {
+                throw new SQLiteException("Downgrade path not supported to version " + i);
+            }
+            Collections.addAll(allCommands, commands);
+        }
+
+        try (SQLiteTransaction t = new SQLiteTransaction(db)) {
+            for (String sql : allCommands) {
+                db.execSQL(sql);
+            }
+            t.commit();
+        }
+    }
+
+    public static DbDowngradeHelper parse(File file) throws JSONException, IOException {
+        JSONObject obj = new JSONObject(new String(IOUtils.toByteArray(file)));
+        DbDowngradeHelper helper = new DbDowngradeHelper(obj.getInt(KEY_VERSION));
+        for (int version = helper.version - 1; version > 0; version--) {
+            if (obj.has(KEY_DOWNGRADE_TO + version)) {
+                JSONArray statements = obj.getJSONArray(KEY_DOWNGRADE_TO + version);
+                String[] parsed = new String[statements.length()];
+                for (int i = 0; i < parsed.length; i++) {
+                    parsed[i] = statements.getString(i);
+                }
+                helper.mStatements.put(version, parsed);
+            }
+        }
+        return helper;
+    }
+
+    public static void updateSchemaFile(File schemaFile, int expectedVersion,
+            Context context, int schemaResId) {
+        try {
+            if (DbDowngradeHelper.parse(schemaFile).version >= expectedVersion) {
+                return;
+            }
+        } catch (Exception e) {
+            // Schema error
+        }
+
+        // Write the updated schema
+        try (FileOutputStream fos = new FileOutputStream(schemaFile);
+            InputStream in = context.getResources().openRawResource(schemaResId)) {
+            IOUtils.copy(in, fos);
+        } catch (IOException e) {
+            Log.e(TAG, "Error writing schema file", e);
+        }
+    }
+}