flutter/packages/flutter_tools/lib/src/base/project_migrator.dart

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:meta/meta.dart';

import 'file_system.dart';
import 'logger.dart';

/// Project is generated from a template on Flutter project creation.
/// Sometimes (due to behavior changes in Xcode, Gradle, etc) these files need to be altered
/// from the original template.
abstract class ProjectMigrator {
  ProjectMigrator(this.logger);

  @protected
  final Logger logger;

  /// Returns whether migration was successful or was skipped.
  bool migrate();

  /// Return null if the line should be deleted.
  @protected
  String migrateLine(String line) {
    return line;
  }

  @protected
  void processFileLines(File file) {
    final List<String> lines = file.readAsLinesSync();

    final StringBuffer newProjectContents = StringBuffer();
    final String basename = file.basename;

    bool migrationRequired = false;
    for (final String line in lines) {
      final String newProjectLine = migrateLine(line);
      if (newProjectLine == null) {
        logger.printTrace('Migrating $basename, removing:');
        logger.printTrace('    $line');
        migrationRequired = true;
        continue;
      }
      if (newProjectLine != line) {
        logger.printTrace('Migrating $basename, replacing:');
        logger.printTrace('    $line');
        logger.printTrace('with:');
        logger.printTrace('    $newProjectLine');
        migrationRequired = true;
      }
      newProjectContents.writeln(newProjectLine);
    }

    if (migrationRequired) {
      logger.printStatus('Upgrading $basename');
      file.writeAsStringSync(newProjectContents.toString());
    }
  }
}

class ProjectMigration {
  ProjectMigration(this.migrators);

  final List<ProjectMigrator> migrators;

  bool run() {
    for (final ProjectMigrator migrator in migrators) {
      if (!migrator.migrate()) {
        // Migration failures should be more robust, with transactions and fallbacks.
        // See https://github.com/flutter/flutter/issues/12573 and
        // https://github.com/flutter/flutter/issues/40460
        return false;
      }
    }
    return true;
  }
}