import 'dart:async';

import 'package:equatable/equatable.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:uto_manager/domain/entities/position_slot.dart';
import 'package:uto_manager/domain/entities/unit_node.dart';
import 'package:uto_manager/domain/repositories/unit_repository.dart';
import 'package:uto_manager/domain/services/unit_tree_service.dart';
import 'package:uto_manager/infrastructure/repositories/drift_position_slot_repository.dart';

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

/// State for the unit tree cubit.
sealed class UnitTreeState extends Equatable {
  const UnitTreeState();
}

/// Initial state before any data is loaded.
class UnitTreeInitial extends UnitTreeState {
  const UnitTreeInitial();

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

/// State while the unit tree is loading.
class UnitTreeLoading extends UnitTreeState {
  const UnitTreeLoading();

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

/// State when the unit tree has been loaded successfully.
class UnitTreeLoaded extends UnitTreeState {
  const UnitTreeLoaded({
    required this.units,
    required this.slots,
    required this.roots,
    this.selectedUnitId,
  });

  /// Flat list of all unit nodes.
  final List<UnitNode> units;

  /// Flat list of all position slots.
  final List<PositionSlot> slots;

  /// Root-level [UnitTreeNode]s (built from units + slots).
  final List<UnitTreeNode> roots;

  /// The currently selected unit ID, or null if none selected.
  final String? selectedUnitId;

  /// Returns the selected [UnitNode], or null.
  UnitNode? get selectedUnit =>
      selectedUnitId == null ? null : units.firstWhere((u) => u.unitId == selectedUnitId);

  /// Returns slots for the selected unit.
  List<PositionSlot> get selectedUnitSlots =>
      selectedUnitId == null ? [] : slots.where((s) => s.unitId == selectedUnitId).toList();

  UnitTreeLoaded copyWith({
    List<UnitNode>? units,
    List<PositionSlot>? slots,
    List<UnitTreeNode>? roots,
    String? selectedUnitId,
    bool clearSelection = false,
  }) {
    return UnitTreeLoaded(
      units: units ?? this.units,
      slots: slots ?? this.slots,
      roots: roots ?? this.roots,
      selectedUnitId: clearSelection ? null : (selectedUnitId ?? this.selectedUnitId),
    );
  }

  @override
  List<Object?> get props => [units, slots, roots, selectedUnitId];
}

/// State when an error occurred loading the unit tree.
class UnitTreeError extends UnitTreeState {
  const UnitTreeError(this.message);

  final String message;

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

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

/// Manages the unit tree state, including loading, selection, and re-parenting.
class UnitTreeCubit extends Cubit<UnitTreeState> {
  UnitTreeCubit({
    required this.unitRepository,
    required this.slotRepository,
    required this.treeService,
  }) : super(const UnitTreeInitial());

  final UnitRepository unitRepository;
  final DriftPositionSlotRepository slotRepository;
  final UnitTreeService treeService;

  StreamSubscription<List<UnitNode>>? _unitSubscription;
  StreamSubscription<List<PositionSlot>>? _slotSubscription;

  List<UnitNode> _units = [];
  List<PositionSlot> _slots = [];

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

  /// Starts watching the database for unit and slot changes.
  void startWatching() {
    emit(const UnitTreeLoading());

    _unitSubscription = unitRepository.watchAll().listen(
      (units) {
        _units = units;
        _rebuild();
      },
      onError: (Object e) => emit(UnitTreeError(e.toString())),
    );

    _slotSubscription = slotRepository.watchAll().listen(
      (slots) {
        _slots = slots;
        _rebuild();
      },
      onError: (Object e) => emit(UnitTreeError(e.toString())),
    );
  }

  void _rebuild() {
    final roots = treeService.buildTree(_units, _slots);
    final currentSelection =
        state is UnitTreeLoaded ? (state as UnitTreeLoaded).selectedUnitId : null;
    emit(UnitTreeLoaded(
        units: _units, slots: _slots, roots: roots, selectedUnitId: currentSelection));
  }

  // ---------------------------------------------------------------------------
  // Selection
  // ---------------------------------------------------------------------------

  /// Selects the unit with [unitId].
  void selectUnit(String unitId) {
    if (state is UnitTreeLoaded) {
      emit((state as UnitTreeLoaded).copyWith(selectedUnitId: unitId));
    }
  }

  /// Clears the current unit selection.
  void clearSelection() {
    if (state is UnitTreeLoaded) {
      emit((state as UnitTreeLoaded).copyWith(clearSelection: true));
    }
  }

  // ---------------------------------------------------------------------------
  // Mutations
  // ---------------------------------------------------------------------------

  /// Adds a new [unit] to the tree.
  Future<void> addUnit(UnitNode unit) async {
    try {
      await unitRepository.insert(unit);
    } catch (e) {
      emit(UnitTreeError(e.toString()));
    }
  }

  /// Re-parents [unitId] under [newParentId] after doctrinal validation.
  Future<bool> reparentUnit(String unitId, String newParentId) async {
    if (state is! UnitTreeLoaded) return false;
    final loaded = state as UnitTreeLoaded;

    final child = loaded.units.firstWhere((u) => u.unitId == unitId);
    final newParent = loaded.units.firstWhere((u) => u.unitId == newParentId);

    final validation = treeService.validateReparent(child, newParent, loaded.units);
    if (!validation.isValid) return false;

    try {
      await unitRepository.reparent(unitId, newParentId);
      return true;
    } catch (e) {
      emit(UnitTreeError(e.toString()));
      return false;
    }
  }

  /// Deletes [unitId] and all its descendants.
  Future<void> deleteSubtree(String unitId) async {
    try {
      await unitRepository.deleteSubtree(unitId);
    } catch (e) {
      emit(UnitTreeError(e.toString()));
    }
  }

  /// Clears all units and slots (template reset).
  Future<void> clearAll() async {
    try {
      await slotRepository.deleteAll();
      await unitRepository.deleteAll();
    } catch (e) {
      emit(UnitTreeError(e.toString()));
    }
  }

  @override
  Future<void> close() {
    _unitSubscription?.cancel();
    _slotSubscription?.cancel();
    return super.close();
  }
}