import 'package:equatable/equatable.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
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';
import 'package:uto_manager/domain/services/validation_isolate.dart';

// ---------------------------------------------------------------------------
// State
// ---------------------------------------------------------------------------

/// State for the validation cubit.
sealed class ValidationState extends Equatable {
  const ValidationState();
}

/// No validation has been run yet.
class ValidationInitial extends ValidationState {
  const ValidationInitial();

  @override
  List<Object?> get props => [];
}

/// Validation is in progress (running in background Isolate).
class ValidationRunning extends ValidationState {
  const ValidationRunning();

  @override
  List<Object?> get props => [];
}

/// Validation completed with a (possibly empty) list of findings.
class ValidationComplete extends ValidationState {
  const ValidationComplete(this.findings);

  final List<ValidationFinding> findings;

  /// All critical findings.
  List<ValidationFinding> get critical =>
      findings.where((f) => f.severity == FindingSeverity.critical).toList();

  /// All warning findings.
  List<ValidationFinding> get warnings =>
      findings.where((f) => f.severity == FindingSeverity.warning).toList();

  /// All advisory findings.
  List<ValidationFinding> get advisories =>
      findings.where((f) => f.severity == FindingSeverity.advisory).toList();

  /// Returns findings for a specific [unitId].
  List<ValidationFinding> findingsForUnit(String unitId) =>
      findings.where((f) => f.unitId == unitId).toList();

  /// Returns the highest-severity finding for [unitId], or null if clean.
  FindingSeverity? worstSeverityForUnit(String unitId) {
    final unitFindings = findingsForUnit(unitId);
    if (unitFindings.isEmpty) return null;
    if (unitFindings.any((f) => f.severity == FindingSeverity.critical)) {
      return FindingSeverity.critical;
    }
    if (unitFindings.any((f) => f.severity == FindingSeverity.warning)) {
      return FindingSeverity.warning;
    }
    return FindingSeverity.advisory;
  }

  /// True if there are no findings.
  bool get isClean => findings.isEmpty;

  @override
  List<Object?> get props => [findings];
}

// ---------------------------------------------------------------------------
// Cubit
// ---------------------------------------------------------------------------

/// Runs the [MtoeValidationEngine] against the current unit tree snapshot
/// and exposes the resulting [ValidationFinding]s to the UI.
///
/// Validation is offloaded to a background [IsolateValidationRunner] so the
/// UI thread is never blocked. The isolate is started lazily on the first
/// [validate] call and kept alive for the lifetime of the cubit.
///
/// Call [validate] whenever the unit tree, slots, or personnel change.
class ValidationCubit extends Cubit<ValidationState> {
  ValidationCubit() : super(const ValidationInitial());

  /// Synchronous fallback engine used when the isolate is not available
  /// (e.g., in unit tests or on platforms that do not support isolates).
  final _syncEngine = const MtoeValidationEngine();

  /// Background isolate runner (lazy-initialized).
  IsolateValidationRunner? _runner;

  // ---------------------------------------------------------------------------
  // Validate
  // ---------------------------------------------------------------------------

  /// Runs all MTOE validation rules against the provided snapshot.
  ///
  /// Attempts to run in a background [IsolateValidationRunner]. Falls back to
  /// synchronous execution if the isolate cannot be started.
  ///
  /// Emits [ValidationRunning] while computing, then [ValidationComplete]
  /// with the results.
  Future<void> validate({
    required List<UnitNode> units,
    required List<PositionSlot> slots,
    required List<PersonnelRecord> personnel,
  }) async {
    emit(const ValidationRunning());

    try {
      // Attempt isolate-based validation.
      final runner = await _getRunner();
      final response = await runner.validate(
        units: units,
        slots: slots,
        personnel: personnel,
      );

      if (response.hasError) {
        // Isolate reported an error — fall back to synchronous.
        final findings = _syncEngine.validate(
          units: units,
          slots: slots,
          personnel: personnel,
        );
        emit(ValidationComplete(findings));
      } else {
        emit(ValidationComplete(response.findings));
      }
    } catch (_) {
      // Isolate unavailable — run synchronously on the UI thread.
      final findings = _syncEngine.validate(
        units: units,
        slots: slots,
        personnel: personnel,
      );
      emit(ValidationComplete(findings));
    }
  }

  /// Clears all findings and resets to the initial state.
  void clear() => emit(const ValidationInitial());

  // ---------------------------------------------------------------------------
  // Lifecycle
  // ---------------------------------------------------------------------------

  /// Returns the shared [IsolateValidationRunner], starting it if needed.
  Future<IsolateValidationRunner> _getRunner() async {
    if (_runner == null) {
      _runner = IsolateValidationRunner();
      await _runner!.start();
    }
    return _runner!;
  }

  @override
  Future<void> close() async {
    await _runner?.dispose();
    _runner = null;
    return super.close();
  }
}