flutter_projects/dart_ex_1/ex_2.dart

mixin Connectable {
  bool isConnected = false;
  void toggleConnection() => isConnected = !isConnected;
}

abstract class SmartDevice {
  final String id;
  String _name;
  bool _powerStatus = false;
  bool _auto_on_off = false;

  static const String brand = "GeminiHome";

  // 1. Standard Constructor with named parameters
  SmartDevice({required this.id, required String name}) : _name = name;

  // 2. Named Constructor: Preset for Office use
  SmartDevice.office({required this.id})
      : _name = "Office Desk Lamp",
        _auto_on_off = true;

  // 3. Named Constructor: Preset for Eco mode
  SmartDevice.eco({required this.id})
      : _name = "Eco Saver Unit",
        _powerStatus = false,
        _auto_on_off = true;

  // 4. Factory Constructor using named parameters
  factory SmartDevice.create({
    required String type,
    required String id,
    required String name,
  }) {
    if (type == 'light') return SmartLight(id: id, name: name);
    return SmartSpeaker(id: id, name: name);
  }

  // Specialized factory for the Office preset
  factory SmartDevice.createOffice({required String id}) {
    return SmartLight.office(id: id);
  }

  String get name => _name;
  set name(String value) => _name = value.trim();

  void performAction();

  void togglePower() {
    _powerStatus = !_powerStatus;
    print('$_name is now ${_powerStatus ? "ON" : "OFF"} (Auto-mode: $_auto_on_off)');
  }
}

class SmartLight extends SmartDevice {
  int brightness = 100;

  // Using 'super' syntax with named parameters
  SmartLight({required super.id, required super.name});

  // Redirecting to parent named constructors
  SmartLight.office({required String id}) : super.office(id: id);
  
  SmartLight.eco({required String id}) : super.eco(id: id);

  @override
  void performAction() {
    print('[$_name] Brightness: $brightness%');
  }
}

class SmartSpeaker extends SmartDevice with Connectable {
  double volume;

  SmartSpeaker({
    required String id,
    required String name,
    this.volume = 0.5,
  })  : assert(volume >= 0 && volume <= 1.0),
        super(id: id, name: name);

  @override
  void performAction() {
    print('[$_name] Volume: ${(volume * 100).toInt()}%. Connected: $isConnected');
  }
}

void main() {
  // --- USAGE ---

  // 1. Using the 'Office' preset with named ID
  final workLamp = SmartLight.office(id: 'OFFICE_01');
  
  // 2. Using the 'Eco' preset with named ID
  final ecoLight = SmartLight.eco(id: 'ECO_99');

  // 3. Standard creation using clear labels for ID and Name
  final customLight = SmartLight(id: 'CUST_01', name: 'My Custom Light');

  // 4. Using the factory with named parameters
  final speaker = SmartDevice.create(
    type: 'speaker', 
    id: 'SPK_01', 
    name: 'Living Room Bass'
  );

  print('--- Testing Presets ---');
  workLamp.performAction();
  workLamp.togglePower();
  
  print('');
  
  ecoLight.performAction();
  ecoLight.togglePower();

  print('');
  speaker.performAction();
}


// You're absolutely right. Understanding *why* we use these features is more important than just knowing the syntax. Let’s break down the rationale and real-world use cases for the structure I built.

// ---

// ## 1. The Abstract Class (`SmartDevice`)
// **Rationale:** You want to define a "contract." Every smart device must have an ID, a name, and an action, but a "generic" smart device doesn't exist in reality—it’s always a specific light, speaker, or thermostat.

// * **Use Case:** In a Large App, you might have a `List<SmartDevice> devices`. You can loop through this list and call `.togglePower()` on every item without knowing if it's a light or a speaker. This is the heart of **Polymorphism**.

// ---

// ## 2. Factory Constructors (`SmartDevice.create`)
// **Rationale:** Normal constructors always create a new instance of the exact class they belong to. A `factory` constructor is more flexible: it can return a subclass or even a cached instance.

// * **Use Case:** **API Parsing.** When you get JSON data from a server, you don't know the device type until you read the data. A factory constructor can look at the "type" field in the JSON and decide to return a `SmartLight` object or a `SmartSpeaker` object automatically.

// ---

// ## 3. Mixins (`with Connectable`)
// **Rationale:** Dart doesn't allow a class to have two parents (Multiple Inheritance) because it gets messy. Mixins allow you to "plug in" shared behavior across unrelated classes.



// * **Use Case:** Imagine you have a `SmartSpeaker` (a device) and a `PhoneApp` (not a device). Both need "WiFi Connection" logic. Instead of copying the code twice, you create a `Connectable` mixin and apply it to both.

// ---

// ## 4. Getters and Setters
// **Rationale:** This is about **Encapsulation**. You should never let outside code touch your internal variables (`_name`) directly. By using a setter, you can "sanitize" the data.

// * **Use Case:** Validation. If a user tries to set a device name to a string full of empty spaces, your setter `set name(value) => _name = value.trim();` automatically cleans it up before it’s saved to your database.

// ---

// ## 5. Redirecting Constructors (`SmartSpeaker.loud`)
// **Rationale:** To avoid "Boilerplate" (repetitive code). If you have a common configuration for a class, you don't want to rewrite the initialization logic.

// * **Use Case:** **Presets.** In a UI, you might have a "Default" button and a "Pro" button. Instead of manually setting 10 different parameters each time, you create a named constructor like `Button.primary()` that redirects to the main constructor with all the "Pro" settings pre-filled.

// ---

// ## 6. Static Members (`static const brand`)
// **Rationale:** Memory efficiency. If you have 1,000 smart lights, you don't need the string "GeminiHome" stored in memory 1,000 times. 

// * **Use Case:** **Configuration & Constants.** Use `static` for things that are "Universal truth" for the class, such as a maximum volume limit or a shared API version number.

// Would you like me to show you how to handle **Interfaces** in Dart, which is the final piece of the OO puzzle?