// Dart 3 – Null-safety
import 'dart:io';

void main() {
  // (7) Final/Const Variables
  const int kMinTemp = 15;
  const int kMaxTemp = 30;

  // (2) Device Status – initial state
  bool lightsOn = false;        // Lights: on/off
  int thermostat = 20;          // Thermostat: 15..30
  bool securityArmed = false;   // Security: armed/disarmed

  // (1) Main Method + (3) User Interaction loop
  while (true) {
    _menu(kMinTemp, kMaxTemp);
    final choice = _readInt();

    if (choice == null) {
      _warn('Invalid input. Enter a number 1–5.');
      continue;
    }

    // (5) Control Flow: switch + if/else
    switch (choice) {
      case 1:
        // Lights toggle
        lightsOn = !lightsOn;
        print('Lights turned ${lightsOn ? "ON" : "OFF"}.');
        break;

      case 2:
        // Set thermostat with validation (4) + (8)
        stdout.write('Enter temperature ($kMinTemp–$kMaxTemp): ');
        final t = _readInt();
        if (t == null || t < kMinTemp || t > kMaxTemp) {
          _warn('Temperature must be between $kMinTemp and $kMaxTemp.');
        } else {
          thermostat = t;
          print('Thermostat set to $thermostat°C.');
        }
        break;

      case 3:
        // Security arm/disarm with string ops (6) + (8)
        stdout.write('Type "arm" or "disarm": ');
        final cmd = stdin.readLineSync()?.trim().toLowerCase();
        if (cmd == 'arm') {
          securityArmed = true;
          print('Security is ${"armed".toUpperCase()}.');
        } else if (cmd == 'disarm') {
          securityArmed = false;
          print('Security is ${"disarmed".toUpperCase()}.');
        } else {
          _warn('Use only: arm / disarm');
        }
        break;

      case 4:
        // (6) Interpolation + FizzBuzz-like rule (5)
        _printStatus(
          lightsOn: lightsOn,
          thermostat: thermostat,
          securityArmed: securityArmed,
        );
        break;

      case 5:
        print('Exiting Smart Home. Goodbye!');
        return;

      default:
        _warn('Choose a valid option (1–5).');
    }
  }
}

void _menu(int minT, int maxT) {
  print('\n=== Smart Home Controller ===');
  print('1) Toggle lights (On/Off)');
  print('2) Set thermostat ($minT–$maxT °C)');
  print('3) Arm/Disarm security system');
  print('4) View system status');
  print('5) Exit');
  stdout.write('Choose an option: ');
}

int? _readInt() {
  final s = stdin.readLineSync();
  return s == null ? null : int.tryParse(s.trim());
}

void _printStatus({
  required bool lightsOn,
  required int thermostat,
  required bool securityArmed,
}) {
  final lightsMsg = lightsOn ? 'ON' : 'OFF';
  final securityMsg = securityArmed ? 'ARMED' : 'DISARMED';

  // FizzBuzz-like message
  final m3 = thermostat % 3 == 0;
  final m5 = thermostat % 5 == 0;
  final dayMsg = (m3 && m5)
      ? 'Perfect Day'
      : (m3 ? 'Cool Day' : (m5 ? 'Warm Day' : ''));

  print('\n--- System Status ---');
  print('Lights: $lightsMsg');
  print('Thermostat: $thermostat°C${dayMsg.isNotEmpty ? " - $dayMsg" : ""}');
  print('Security: $securityMsg');
}

void _warn(String msg) => print('⚠️  $msg');