Created Android scoped storage migration method (#559)

* Created Android migration script

* Update AsyncStorageMigration.java

* Removed delete step

* Revert "Removed delete step"

This reverts commit 6fbaf4c.

* [feedback] Remove private context

* [feedback] inline statement

* Update AsyncStorageMigration.java

* rename migration module

* [feedback] Use correct ReactDatabaseSupplier

android/src/main/java/com/reactnativecommunity/asyncstorage/AsyncStorageExpoMigration.java

@@ -0,0 +1,154 @@
+package com.reactnativecommunity.asyncstorage;
+
+import android.content.Context;
+import android.os.Build;
+import android.util.Log;
+
+import androidx.annotation.RequiresApi;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.nio.channels.FileChannel;
+import java.nio.file.Files;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.util.ArrayList;
+
+// A utility class that migrates a scoped AsyncStorage database to RKStorage.
+// This utility only runs if the RKStorage file has not been created yet.
+public class AsyncStorageExpoMigration {
+    static final String LOG_TAG = "AsyncStorageExpoMigration";
+
+    public static void migrate(Context context) {
+        // Only migrate if the default async storage file does not exist.
+        if (isAsyncStorageDatabaseCreated(context)) {
+            return;
+        }
+
+        ArrayList<File> expoDatabases = getExpoDatabases(context);
+
+        File expoDatabase = getLastModifiedFile(expoDatabases);
+
+        if (expoDatabase == null) {
+            Log.v(LOG_TAG, "No scoped database found");
+            return;
+        }
+
+        try {
+            // Create the storage file
+            ReactDatabaseSupplier.getInstance(context).get();
+            copyFile(new FileInputStream(expoDatabase), new FileOutputStream(context.getDatabasePath(ReactDatabaseSupplier.DATABASE_NAME)));
+            Log.v(LOG_TAG, "Migrated most recently modified database " + expoDatabase.getName() + " to RKStorage");
+        } catch (Exception e) {
+            Log.v(LOG_TAG, "Failed to migrate scoped database " + expoDatabase.getName());
+            e.printStackTrace();
+            return;
+        }
+
+        try {
+            for (File file : expoDatabases) {
+                if (file.delete()) {
+                    Log.v(LOG_TAG, "Deleted scoped database " + file.getName());
+                } else {
+                    Log.v(LOG_TAG, "Failed to delete scoped database " + file.getName());
+                }
+            }
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+
+        Log.v(LOG_TAG, "Completed the scoped AsyncStorage migration");
+    }
+
+    private static boolean isAsyncStorageDatabaseCreated(Context context) {
+        return context.getDatabasePath(ReactDatabaseSupplier.DATABASE_NAME).exists();
+    }
+
+    // Find all database files that the user may have created while using Expo.
+    private static ArrayList<File> getExpoDatabases(Context context) {
+        ArrayList<File> scopedDatabases = new ArrayList<>();
+        try {
+            File databaseDirectory = context.getDatabasePath("noop").getParentFile();
+            File[] directoryListing = databaseDirectory.listFiles();
+            if (directoryListing != null) {
+                for (File child : directoryListing) {
+                    // Find all databases matching the Expo scoped key, and skip any database journals.
+                    if (child.getName().startsWith("RKStorage-scoped-experience-") && !child.getName().endsWith("-journal")) {
+                        scopedDatabases.add(child);
+                    }
+                }
+            }
+        } catch (Exception e) {
+            // Just in case anything happens catch and print, file system rules can tend to be different across vendors.
+            e.printStackTrace();
+        }
+        return scopedDatabases;
+    }
+
+    // Returns the most recently modified file.
+    // If a user publishes an app with Expo, then changes the slug 
+    // and publishes again, a new database will be created. 
+    // We want to select the most recent database and migrate it to RKStorage.
+    private static File getLastModifiedFile(ArrayList<File> files) {
+        if (files.size() == 0) {
+            return null;
+        }
+        long lastMod = -1;
+        File lastModFile = null;
+        for (File child : files) {
+            long modTime = getLastModifiedTimeInMillis(child);
+            if (modTime > lastMod) {
+                lastMod = modTime;
+                lastModFile = child;
+            }
+        }
+        if (lastModFile != null) {
+            return lastModFile;
+        }
+
+        return files.get(0);
+    }
+
+    private static long getLastModifiedTimeInMillis(File file) {
+        try {
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+                return getLastModifiedTimeFromBasicFileAttrs(file);
+            } else {
+                return file.lastModified();
+            }
+        } catch (Exception e) {
+            e.printStackTrace();
+            return -1;
+        }
+    }
+
+    @RequiresApi(Build.VERSION_CODES.O)
+    private static long getLastModifiedTimeFromBasicFileAttrs(File file) {
+        try {
+            return Files.readAttributes(file.toPath(), BasicFileAttributes.class).creationTime().toMillis();
+        } catch (Exception e) {
+            return -1;
+        }
+    }
+
+    private static void copyFile(FileInputStream fromFile, FileOutputStream toFile) throws IOException {
+        FileChannel fromChannel = null;
+        FileChannel toChannel = null;
+        try {
+            fromChannel = fromFile.getChannel();
+            toChannel = toFile.getChannel();
+            fromChannel.transferTo(0, fromChannel.size(), toChannel);
+        } finally {
+            try {
+                if (fromChannel != null) {
+                    fromChannel.close();
+                }
+            } finally {
+                if (toChannel != null) {
+                    toChannel.close();
+                }
+            }
+        }
+    }
+}

android/src/main/java/com/reactnativecommunity/asyncstorage/AsyncStorageModule.java

@@ -91,8 +91,12 @@ public AsyncStorageModule(ReactApplicationContext reactContext) {
   @VisibleForTesting
   AsyncStorageModule(ReactApplicationContext reactContext, Executor executor) {
     super(reactContext);
+    // The migration MUST run before the AsyncStorage database is created for the first time.
+    AsyncStorageExpoMigration.migrate(reactContext);
+
     this.executor = new SerialExecutor(executor);
     reactContext.addLifecycleEventListener(this);
+    // Creating the database MUST happen after the migration.
     mReactDatabaseSupplier = ReactDatabaseSupplier.getInstance(reactContext);
   }