import 'dart:isolate';

import 'package:uto_manager/domain/entities/personnel_record.dart';
import 'package:uto_manager/domain/entities/position_slot.dart';
import 'package:uto_manager/domain/entities/unit_node.dart';
import 'package:uto_manager/domain/services/mtoe_validation_engine.dart';

// ---------------------------------------------------------------------------
// Message types
// ---------------------------------------------------------------------------

/// Request message sent to the validation isolate.
class ValidationRequest {
  const ValidationRequest({
    required this.units,
    required this.slots,
    required this.personnel,
    required this.replyPort,
  });

  final List<UnitNode> units;
  final List<PositionSlot> slots;
  final List<PersonnelRecord> personnel;
  final SendPort replyPort;
}

/// Response message returned from the validation isolate.
class ValidationResponse {
  const ValidationResponse({
    required this.findings,
    this.error,
  });

  final List<ValidationFinding> findings;
  final String? error;

  bool get hasError => error != null;
}

// ---------------------------------------------------------------------------
// Isolate entry point
// ---------------------------------------------------------------------------

/// Entry point for the background validation isolate.
///
/// Receives [ValidationRequest] messages on [receivePort], runs the
/// [MtoeValidationEngine], and sends a [ValidationResponse] back via the
/// request's [ValidationRequest.replyPort].
void validationIsolateEntryPoint(SendPort mainSendPort) {
  final receivePort = ReceivePort();
  // Send our receive port to the main isolate so it can send us requests.
  mainSendPort.send(receivePort.sendPort);

  const engine = MtoeValidationEngine();

  receivePort.listen((dynamic message) {
    if (message is ValidationRequest) {
      try {
        final findings = engine.validate(
          units: message.units,
          slots: message.slots,
          personnel: message.personnel,
        );
        message.replyPort.send(ValidationResponse(findings: findings));
      } catch (e) {
        message.replyPort.send(
          ValidationResponse(findings: const [], error: e.toString()),
        );
      }
    }
  });
}

// ---------------------------------------------------------------------------
// IsolateValidationRunner
// ---------------------------------------------------------------------------

/// Manages a long-lived background [Isolate] for running MTOE validation
/// without blocking the UI thread.
///
/// Usage:
/// ```dart
/// final runner = IsolateValidationRunner();
/// await runner.start();
/// final findings = await runner.validate(units: ..., slots: ..., personnel: ...);
/// await runner.dispose();
/// ```
class IsolateValidationRunner {
  Isolate? _isolate;
  SendPort? _isolateSendPort;
  bool _started = false;

  /// Whether the isolate has been started and is ready to accept requests.
  bool get isStarted => _started;

  /// Starts the background validation isolate.
  ///
  /// Must be called before [validate]. Safe to call multiple times — subsequent
  /// calls are no-ops if the isolate is already running.
  Future<void> start() async {
    if (_started) return;

    final receivePort = ReceivePort();
    _isolate = await Isolate.spawn(
      validationIsolateEntryPoint,
      receivePort.sendPort,
      debugName: 'MtoeValidationIsolate',
    );

    // Wait for the isolate to send back its receive port.
    _isolateSendPort = await receivePort.first as SendPort;
    _started = true;
  }

  /// Runs MTOE validation in the background isolate.
  ///
  /// Returns a [ValidationResponse] with the findings, or an error response
  /// if the isolate encountered an exception.
  ///
  /// Throws [StateError] if [start] has not been called.
  Future<ValidationResponse> validate({
    required List<UnitNode> units,
    required List<PositionSlot> slots,
    required List<PersonnelRecord> personnel,
  }) async {
    if (!_started || _isolateSendPort == null) {
      throw StateError(
        'IsolateValidationRunner.start() must be called before validate().',
      );
    }

    final replyPort = ReceivePort();
    _isolateSendPort!.send(
      ValidationRequest(
        units: units,
        slots: slots,
        personnel: personnel,
        replyPort: replyPort.sendPort,
      ),
    );

    final response = await replyPort.first as ValidationResponse;
    replyPort.close();
    return response;
  }

  /// Shuts down the background isolate and releases resources.
  Future<void> dispose() async {
    _isolate?.kill(priority: Isolate.immediate);
    _isolate = null;
    _isolateSendPort = null;
    _started = false;
  }
}