#457 Improve ForceFlatToSqlite conversion

- Change ForceFlatToSqlite converter to use a generic datasource destination (i.e. can be used for Flat2MySQL later)
- Add tests, including for FlatFile
- Check that user is not present in destination datasource before adding
- Persist last location from flatfile as well

src/main/java/fr/xephi/authme/util/MigrationService.java

@@ -5,6 +5,8 @@ import fr.xephi.authme.cache.auth.PlayerAuth;
 import fr.xephi.authme.converter.ForceFlatToSqlite;
 import fr.xephi.authme.datasource.DataSource;
 import fr.xephi.authme.datasource.DataSourceType;
+import fr.xephi.authme.datasource.FlatFile;
+import fr.xephi.authme.datasource.SQLite;
 import fr.xephi.authme.security.HashAlgorithm;
 import fr.xephi.authme.security.crypts.HashedPassword;
 import fr.xephi.authme.security.crypts.SHA256;
@@ -58,12 +60,17 @@ public final class MigrationService {
         if (DataSourceType.FILE == settings.getProperty(DatabaseSettings.BACKEND)) {
             ConsoleLogger.showError("FlatFile backend has been detected and is now deprecated; it will be changed "
                 + "to SQLite... Connection will be impossible until conversion is done!");
-            ForceFlatToSqlite converter = new ForceFlatToSqlite(dataSource, settings);
-            DataSource result = converter.run();
-            if (result == null) {
-                throw new IllegalStateException("Error during conversion from flatfile to SQLite");
-            } else {
-                return result;
+            FlatFile flatFile = (FlatFile) dataSource;
+            try {
+                SQLite sqlite = new SQLite(settings);
+                ForceFlatToSqlite converter = new ForceFlatToSqlite(flatFile, sqlite);
+                converter.run();
+                settings.setProperty(DatabaseSettings.BACKEND, DataSourceType.SQLITE);
+                settings.save();
+                return sqlite;
+            } catch (Exception e) {
+                ConsoleLogger.logException("Error during conversion from Flatfile to SQLite", e);
+                throw new IllegalStateException(e);
             }
         }
         return null;