import 'dart:async';
import 'dart:convert' show jsonDecode;

import 'package:isolation/isolation.dart';

typedef JsonMap = Map<String, Object?>;

/// Main isolate
void main() => Future<void>(() async {
      // Create a new isolate controller
      final controller = IsolateController<String, JsonMap>(
        _parser,    // Isolate function
        lazy: true, // The isolate will not be created until the first message
      )
       // Add few messages to the isolate:
       ..add('{}')
       ..add('{"field": 123}')
       ..add('{"fizz": "buzz", "value": 2, "undefined": null}');
      // Listen messages from slave isolate
      await controller.stream.take(3).forEach(print);
      // Gracefully closing connection and finally kill slave isolate
      await controller.close(force: false);
    });

/// Slave isolate for parsing JSON, where you can subscribe to the stream
/// from the main isolate and send the result back through the controller.
Future<void> _parser(IsolateController<JsonMap, String> controller) =>
    controller.stream.forEach((json) {
      final result = jsonDecode(json) as Object?;
      (result is JsonMap)
          ? controller.add(result)
          : controller.addError(const FormatException('Invalid JSON'));
    });