build_runner/lib/src/server/build_updates_client/reloading_manager.dart

// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'dart:async';
import 'dart:collection';

import 'package:graphs/graphs.dart' as graphs;

import 'module.dart';

class HotReloadFailedException implements Exception {
  HotReloadFailedException(this._s);

  @override
  String toString() => "HotReloadFailedException: '$_s'";
  final String _s;
}

/// Handles reloading order and hooks invocation
class ReloadingManager {
  final Future<Module> Function(String) _reloadModule;
  final Module Function(String) _moduleLibraries;
  final void Function() _reloadPage;
  final List<String> Function(String moduleId) _moduleParents;
  final Iterable<String> Function() _allModules;

  final Map<String, int> _moduleOrdering = {};
  SplayTreeSet<String> _dirtyModules;
  Completer<void> _running = Completer()..complete();

  int moduleTopologicalCompare(String module1, String module2) {
    var topological =
        Comparable.compare(_moduleOrdering[module2], _moduleOrdering[module1]);
    // If modules are in cycle (same strongly connected component) compare their
    // string id, to ensure total ordering for SplayTreeSet uniqueness.
    return topological != 0 ? topological : module1.compareTo(module2);
  }

  void updateGraph() {
    var allModules = _allModules();
    var stronglyConnectedComponents =
        graphs.stronglyConnectedComponents(allModules, _moduleParents);
    _moduleOrdering.clear();
    for (var i = 0; i < stronglyConnectedComponents.length; i++) {
      for (var module in stronglyConnectedComponents[i]) {
        _moduleOrdering[module] = i;
      }
    }
  }

  ReloadingManager(this._reloadModule, this._moduleLibraries, this._reloadPage,
      this._moduleParents, this._allModules) {
    _dirtyModules = SplayTreeSet(moduleTopologicalCompare);
  }

  Future<void> reload(List<String> modules) async {
    _dirtyModules.addAll(modules);

    // As function is async, it can potentially be called second time while
    // first invocation is still running. In this case just mark as dirty and
    // wait until loop from the first call will do the work
    if (!_running.isCompleted) return await _running.future;
    _running = Completer();

    var reloadedModules = 0;

    try {
      while (_dirtyModules.isNotEmpty) {
        var moduleId = _dirtyModules.first;
        _dirtyModules.remove(moduleId);
        ++reloadedModules;

        var existing = _moduleLibraries(moduleId);
        var data = existing.onDestroy();

        var newVersion = await _reloadModule(moduleId);
        var success = newVersion.onSelfUpdate(data);
        if (success == true) continue;
        if (success == false) {
          print("Module '$moduleId' is marked as unreloadable. "
              'Firing full page reload.');
          _reloadPage();
          _running.complete();
          return;
        }

        var parentIds = _moduleParents(moduleId);
        if (parentIds == null || parentIds.isEmpty) {
          print("Module reloading wasn't handled by any of parents. "
              'Firing full page reload.');
          _reloadPage();
          _running.complete();
          return;
        }
        parentIds.sort(moduleTopologicalCompare);
        for (var parentId in parentIds) {
          var parentModule = _moduleLibraries(parentId);
          success = parentModule.onChildUpdate(moduleId, newVersion, data);
          if (success == true) continue;
          if (success == false) {
            print("Module '$moduleId' is marked as unreloadable. "
                'Firing full page reload.');
            _reloadPage();
            _running.complete();
            return;
          }
          _dirtyModules.add(parentId);
        }
      }
      print('$reloadedModules modules were hot-reloaded.');
    } on HotReloadFailedException catch (e) {
      print('Error during script reloading. Firing full page reload. $e');
      _reloadPage();
    }
    _running.complete();
  }
}