GitJournal/lib/core/md_yaml_doc_loader.dart

import 'dart:io';
import 'dart:isolate';

import 'package:synchronized/synchronized.dart';

import 'package:gitjournal/core/md_yaml_doc.dart';
import 'package:gitjournal/core/md_yaml_doc_codec.dart';

class MdYamlDocLoader {
  Isolate _isolate;
  ReceivePort _receivePort = ReceivePort();
  SendPort _sendPort;

  var _loadingLock = Lock();

  Future<void> _initIsolate() async {
    if (_isolate != null && _sendPort != null) return;

    return await _loadingLock.synchronized(() async {
      if (_isolate != null && _sendPort != null) return;
      if (_isolate != null) {
        _isolate.kill(priority: Isolate.immediate);
        _isolate = null;
      }
      _isolate = await Isolate.spawn(_isolateMain, _receivePort.sendPort);

      var data = await _receivePort.first;
      assert(data is SendPort);
      _sendPort = data as SendPort;
    });
  }

  Future<MdYamlDoc> loadDoc(String filePath) async {
    await _initIsolate();

    final file = File(filePath);
    if (!file.existsSync()) {
      throw MdYamlDocNotFoundException(filePath);
    }

    var rec = ReceivePort();
    _sendPort.send(_LoadingMessage(filePath, rec.sendPort));

    var data = await rec.first;
    assert(data is MdYamlDoc);

    return data;
  }
}

class _LoadingMessage {
  String filePath;
  SendPort sendPort;

  _LoadingMessage(this.filePath, this.sendPort);
}

void _isolateMain(SendPort toMainSender) {
  ReceivePort fromMainRec = ReceivePort();
  toMainSender.send(fromMainRec.sendPort);

  final _serializer = MarkdownYAMLCodec();

  fromMainRec.listen((data) async {
    assert(data is _LoadingMessage);
    var msg = data as _LoadingMessage;

    final file = File(msg.filePath);
    final fileData = await file.readAsString();
    var doc = _serializer.decode(fileData);

    msg.sendPort.send(doc);
  });
}

class MdYamlDocNotFoundException implements Exception {
  final String filePath;
  MdYamlDocNotFoundException(this.filePath);

  @override
  String toString() => "MdYamlDocNotFoundException: $filePath";
}