import 'dart:convert';

import 'package:uto_manager/domain/entities/authorized_rank.dart';
import 'package:uto_manager/domain/entities/doctrinal_branch.dart';
import 'package:uto_manager/domain/entities/echelon.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/value_objects/duty_mos.dart';

/// Codec for serializing and deserializing the full unit tree (units +
/// position slots + personnel) to/from a structured JSON representation.
///
/// The JSON schema is:
/// ```json
/// {
///   "version": 1,
///   "exportedAt": "<ISO-8601>",
///   "units": [ { ...UnitNode fields } ],
///   "slots": [ { ...PositionSlot fields } ],
///   "personnel": [ { ...PersonnelRecord fields } ]
/// }
/// ```
class UnitTreeCodec {
  const UnitTreeCodec();

  static const int _schemaVersion = 1;

  // ---------------------------------------------------------------------------
  // Encode
  // ---------------------------------------------------------------------------

  /// Encodes [units], [slots], and [personnel] into a JSON string.
  String encode({
    required List<UnitNode> units,
    required List<PositionSlot> slots,
    required List<PersonnelRecord> personnel,
  }) {
    final map = encodeToMap(units: units, slots: slots, personnel: personnel);
    return const JsonEncoder.withIndent('  ').convert(map);
  }

  /// Encodes [units], [slots], and [personnel] into a [Map].
  Map<String, dynamic> encodeToMap({
    required List<UnitNode> units,
    required List<PositionSlot> slots,
    required List<PersonnelRecord> personnel,
  }) {
    return {
      'version': _schemaVersion,
      'exportedAt': DateTime.now().toUtc().toIso8601String(),
      'units': units.map(_encodeUnit).toList(),
      'slots': slots.map(_encodeSlot).toList(),
      'personnel': personnel.map(_encodePersonnel).toList(),
    };
  }

  // ---------------------------------------------------------------------------
  // Decode
  // ---------------------------------------------------------------------------

  /// Decodes a JSON string into a [UnitTreeSnapshot].
  ///
  /// Throws [FormatException] if the JSON is malformed or the schema version
  /// is unsupported.
  UnitTreeSnapshot decode(String json) {
    final dynamic raw = jsonDecode(json);
    if (raw is! Map<String, dynamic>) {
      throw const FormatException('Root JSON element must be an object.');
    }
    return decodeFromMap(raw);
  }

  /// Decodes a [Map] into a [UnitTreeSnapshot].
  UnitTreeSnapshot decodeFromMap(Map<String, dynamic> map) {
    final version = map['version'] as int?;
    if (version == null || version != _schemaVersion) {
      throw FormatException(
        'Unsupported schema version: $version. Expected $_schemaVersion.',
      );
    }

    final unitsList = (map['units'] as List<dynamic>? ?? [])
        .cast<Map<String, dynamic>>()
        .map(_decodeUnit)
        .toList();

    final slotsList = (map['slots'] as List<dynamic>? ?? [])
        .cast<Map<String, dynamic>>()
        .map(_decodeSlot)
        .toList();

    final personnelList = (map['personnel'] as List<dynamic>? ?? [])
        .cast<Map<String, dynamic>>()
        .map(_decodePersonnel)
        .toList();

    return UnitTreeSnapshot(
      units: unitsList,
      slots: slotsList,
      personnel: personnelList,
    );
  }

  // ---------------------------------------------------------------------------
  // Unit encoding/decoding
  // ---------------------------------------------------------------------------

  Map<String, dynamic> _encodeUnit(UnitNode unit) => {
        'unitId': unit.unitId,
        'echelon': unit.echelon.name,
        'branch': unit.branch.name,
        'parentUnitId': unit.parentUnitId,
        'name': unit.name,
        'isKeyLeader': unit.isKeyLeader,
      };

  UnitNode _decodeUnit(Map<String, dynamic> map) {
    return UnitNode(
      unitId: map['unitId'] as String,
      echelon: Echelon.values.firstWhere((e) => e.name == map['echelon']),
      branch: DoctrinalBranch.values.firstWhere((b) => b.name == map['branch']),
      parentUnitId: map['parentUnitId'] as String?,
      name: map['name'] as String,
      isKeyLeader: map['isKeyLeader'] as bool? ?? false,
    );
  }

  // ---------------------------------------------------------------------------
  // Slot encoding/decoding
  // ---------------------------------------------------------------------------

  Map<String, dynamic> _encodeSlot(PositionSlot slot) => {
        'slotId': slot.slotId,
        'unitId': slot.unitId,
        'positionTitle': slot.positionTitle,
        'dutyMos': slot.dutyMos.code,
        'authorizedRank': slot.authorizedRank.name,
        'isKeyLeader': slot.isKeyLeader,
        'assignedPersonnelId': slot.assignedPersonnelId,
      };

  PositionSlot _decodeSlot(Map<String, dynamic> map) {
    return PositionSlot(
      slotId: map['slotId'] as String,
      unitId: map['unitId'] as String,
      positionTitle: map['positionTitle'] as String,
      dutyMos: DutyMos.unvalidated(map['dutyMos'] as String),
      authorizedRank: AuthorizedRank.values.firstWhere((r) => r.name == map['authorizedRank']),
      isKeyLeader: map['isKeyLeader'] as bool? ?? false,
      assignedPersonnelId: map['assignedPersonnelId'] as String?,
    );
  }

  // ---------------------------------------------------------------------------
  // Personnel encoding/decoding
  // ---------------------------------------------------------------------------

  Map<String, dynamic> _encodePersonnel(PersonnelRecord record) => {
        'soldierId': record.soldierId,
        'name': record.name,
        'primaryMos': record.primaryMos.code,
        'payGrade': record.payGrade.name,
        'qualifications': record.qualifications,
        'readinessState': record.readinessState.name,
        'assignedSlotId': record.assignedSlotId,
      };

  PersonnelRecord _decodePersonnel(Map<String, dynamic> map) {
    return PersonnelRecord(
      soldierId: map['soldierId'] as String,
      name: map['name'] as String,
      primaryMos: DutyMos.unvalidated(map['primaryMos'] as String),
      payGrade: AuthorizedRank.values.firstWhere((r) => r.name == map['payGrade']),
      qualifications: (map['qualifications'] as List<dynamic>? ?? []).cast<String>(),
      readinessState: ReadinessState.values.firstWhere(
        (s) => s.name == map['readinessState'],
      ),
      assignedSlotId: map['assignedSlotId'] as String?,
    );
  }
}

/// A decoded snapshot of the full unit tree.
class UnitTreeSnapshot {
  const UnitTreeSnapshot({
    required this.units,
    required this.slots,
    required this.personnel,
  });

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