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### Execution Output of Facade Example

Source: https://refactoringguru.cn/design-patterns/facade/php/example

The expected console output when running the YouTubeDownloader facade example.

```text
Fetching video metadata from youtube...
Saving video file to a temporary file...
Processing source video...
Normalizing and resizing the video to smaller dimensions...
Capturing preview image...
Saving video in target formats...
Done!
```

--------------------------------

### Example Output

Source: https://refactoringguru.cn/design-patterns/abstract-factory/rust/example

Expected output when running the application.

```text
Windows button has pressed
Windows button has pressed
Windows checkbox has switched
Windows checkbox has switched
```

--------------------------------

### Execution Output of Template Method Example

Source: https://refactoringguru.cn/design-patterns/template-method/php/example

Shows the console output when running the social network posting example.

```text
Username:
> neo
Password:
> 123123
Message:
> What is the Matrix?

Choose the social network to post the message:
1 - Facebook
2 - Twitter
> 1

Checking user's credentials...
Name: neo
Password: ******
.....

Facebook: 'neo' has logged in successfully.
Facebook: 'neo' has posted 'What is the Matrix?'.
Facebook: 'neo' has been logged out.
```

--------------------------------

### State Pattern Usage Demonstration

Source: https://refactoringguru.cn/design-patterns/state/php/example

Example usage showing how to initialize an invoice and perform state transitions, including error handling for invalid transitions.

```php
try {
    echo "=== Invoice State Pattern Demo ===\n\n";

    // Create a new invoice (starts in draft state)
    $invoice = new Invoice(1001, 1500.00);
    echo "Created invoice: " . json_encode($invoice->getInfo()) . "\n\n";

    // Scenario 1: Draft -> Open -> Paid
    echo "--- Scenario 1: Draft -> Open -> Paid ---\n";
    $invoice->finalize(); // Draft -> Open
    echo "Current state: " . $invoice->getStateName() . "\n";

    $invoice->pay(); // Open -> Paid
    echo "Current state: " . $invoice->getStateName() . "\n";

    // Try to pay again (should fail)
    try {
        $invoice->pay();
    } catch (InvalidStateTransitionException $e) {
        echo "Expected error: " . $e->getMessage() . "\n";
    }

    echo "\n--- Scenario 2: Draft -> Open -> Void ---\n";
    $invoice2 = new Invoice(1002, 750.00);
    $invoice2->finalize(); // Draft -> Open
    $invoice2->void(); // Open -> Void
    echo "Invoice 2 state: " . $invoice2->getStateName() . "\n";
```

--------------------------------

### Execution Output of Command Pattern Example

Source: https://refactoringguru.cn/design-patterns/command/swift/example

Displays the console output generated by the Command pattern implementation, showing the sequence of actions and cancellations.

```text
User: Hey Siri, I am leaving my home
Siri: performing leaveHome-action

User: Hey Siri, I am leaving my work in 3 minutes
Siri: performing leaveWork-action

User: Hey Siri, I am still working
Siri: canceling leaveWork-action

DoorOperation: Doors are closed via HomeKit.
WindowOperation: Windows are closed via HomeKit.
TaxiOperation: operation is canceled
```

--------------------------------

### Client Usage Demonstration

Source: https://refactoringguru.cn/design-patterns/memento/php/example

Demonstrates initializing the configuration manager, performing updates, and utilizing the history manager for undo operations.

```php
echo "=== Configuration Manager with Memento Pattern Demo ===\n\n";

/**
 * Example 1: Basic configuration management with backup/restore
 */
echo "--- Example 1: Basic Configuration Management ---\n";

// Initialize configuration manager with default settings
$config = new ConfigManager([
    'maintenance_mode' => false,
    'theme' => 'light',
    'seo' => ['title' => 'My Website', 'description' => 'Welcome to my site!'],
    'debug' => false,
    'max_users' => 1000
]);

// Create history manager
$history = new ConfigHistory($config);

echo "\nInitial configuration:\n";
print_r($config->getConfig());

/**
 * Example 2: Making changes with backups
 */
echo "\n--- Example 2: Making Changes with Backups ---\n";

// Create backup before making changes
$history->backup();

// Update theme settings
$config->updateConfig([
    'theme' => 'dark',
    'theme_options' => ['sidebar' => 'collapsed', 'font_size' => 'large']
]);

echo "\nAfter theme update:\n";
print_r($config->getConfig());

// Create another backup
$history->backup();

// Enable maintenance mode
$config->enableMaintenanceMode();

echo "\nAfter enabling maintenance mode:\n";
print_r($config->getConfig());

/**
 * Example 3: Demonstrating undo functionality
 */
echo "\n--- Example 3: Undo Functionality ---\n";

// Show current history
$history->showHistory();

// Undo last change (maintenance mode)
echo "Undoing maintenance mode activation...\n";
$history->undo();

echo "\nAfter first undo:\n";
print_r($config->getConfig());

// Undo theme changes
echo "\nUndoing theme changes...\n";
$history->undo();

echo "\nAfter second undo (back to original):\n";
print_r($config->getConfig());

/**
 * Example 4: Multiple configuration scenarios
 */
echo "\n--- Example 4: Multiple Configuration Scenarios ---\n";
```

--------------------------------

### Configure and Run Application

Source: https://refactoringguru.cn/design-patterns/abstract-factory/java/example

Demonstrates runtime selection of the factory based on environment configuration.

```java
package refactoring_guru.abstract_factory.example;

import refactoring_guru.abstract_factory.example.app.Application;
import refactoring_guru.abstract_factory.example.factories.GUIFactory;
import refactoring_guru.abstract_factory.example.factories.MacOSFactory;
import refactoring_guru.abstract_factory.example.factories.WindowsFactory;

/**
 * Demo class. Everything comes together here.
 */
public class Demo {

    /**
     * Application picks the factory type and creates it in run time (usually at
     * initialization stage), depending on the configuration or environment
     * variables.
     */
    private static Application configureApplication() {
        Application app;
        GUIFactory factory;
        String osName = System.getProperty("os.name").toLowerCase();
        if (osName.contains("mac")) {
            factory = new MacOSFactory();
        } else {
            factory = new WindowsFactory();
        }
        app = new Application(factory);
        return app;
    }

    public static void main(String[] args) {
        Application app = configureApplication();
        app.paint();
    }
}
```

--------------------------------

### Main Entry Point

Source: https://refactoringguru.cn/design-patterns/builder/cpp/example

Initializes the director and executes the client code.

```cpp
int main(){
    Director* director= new Director();
    ClientCode(*director);
    delete director;
    return 0;    
}
```

--------------------------------

### Initialize Proxy Demo

Source: https://refactoringguru.cn/design-patterns/proxy/java/example

The main entry point that compares the performance of a naive downloader against one using the caching proxy.

```java
package refactoring_guru.proxy.example;

import refactoring_guru.proxy.example.downloader.YouTubeDownloader;
import refactoring_guru.proxy.example.proxy.YouTubeCacheProxy;
import refactoring_guru.proxy.example.some_cool_media_library.ThirdPartyYouTubeClass;

public class Demo {

    public static void main(String[] args) {
        YouTubeDownloader naiveDownloader = new YouTubeDownloader(new ThirdPartyYouTubeClass());
        YouTubeDownloader smartDownloader = new YouTubeDownloader(new YouTubeCacheProxy());

        long naive = test(naiveDownloader);
        long smart = test(smartDownloader);
        System.out.print("Time saved by caching proxy: " + (naive - smart) + "ms");

    }

    private static long test(YouTubeDownloader downloader) {
        long startTime = System.currentTimeMillis();

        // User behavior in our app:
        downloader.renderPopularVideos();
        downloader.renderVideoPage("catzzzzzzzzz");
        downloader.renderPopularVideos();
        downloader.renderVideoPage("dancesvideoo");
        // Users might visit the same page quite often.
        downloader.renderVideoPage("catzzzzzzzzz");
        downloader.renderVideoPage("someothervid");

        long estimatedTime = System.currentTimeMillis() - startTime;
        System.out.print("Time elapsed: " + estimatedTime + "ms\n");
        return estimatedTime;
    }
}
```

--------------------------------

### Execution Output of Abstract Factory

Source: https://refactoringguru.cn/design-patterns/abstract-factory/typescript/example

The console output generated by running the TypeScript example.

```text
Client: Testing client code with the first factory type...
The result of the product B1.
The result of the B1 collaborating with the (The result of the product A1.)

Client: Testing the same client code with the second factory type...
The result of the product B2.
The result of the B2 collaborating with the (The result of the product A2.)
```

--------------------------------

### Factory Method Execution Output

Source: https://refactoringguru.cn/design-patterns/factory-method/swift/example

The console output resulting from the execution of the Factory Method example.

```text
Info is presented over Wifi: Very important info of the presentation
Info is presented over Bluetooth: Very important info of the presentation
```

--------------------------------

### Demo Class Initialization

Source: https://refactoringguru.cn/design-patterns/state/java/example

Entry point for the application that initializes the player and the UI.

```java
package refactoring_guru.state.example;

import refactoring_guru.state.example.ui.Player;
import refactoring_guru.state.example.ui.UI;

/**
 * Demo class. Everything comes together here.
 */
public class Demo {
    public static void main(String[] args) {
        Player player = new Player();
        UI ui = new UI(player);
        ui.init();
    }
}
```

--------------------------------

### Demo Initialization

Source: https://refactoringguru.cn/design-patterns/mediator/java/example

Main entry point that registers components with the mediator and launches the GUI.

```java
package refactoring_guru.mediator.example;

import refactoring_guru.mediator.example.components.*;
import refactoring_guru.mediator.example.mediator.Editor;
import refactoring_guru.mediator.example.mediator.Mediator;

import javax.swing.*;

/**
 * Demo class. Everything comes together here.
 */
public class Demo {
    public static void main(String[] args) {
        Mediator mediator = new Editor();

        mediator.registerComponent(new Title());
        mediator.registerComponent(new TextBox());
        mediator.registerComponent(new AddButton());
        mediator.registerComponent(new DeleteButton());
        mediator.registerComponent(new SaveButton());
        mediator.registerComponent(new List(new DefaultListModel()));
        mediator.registerComponent(new Filter());

        mediator.createGUI();
    }
}
```

--------------------------------

### Decorator Pattern Execution Output

Source: https://refactoringguru.cn/design-patterns/decorator/csharp/example

Displays the console output resulting from the execution of the conceptual example.

```text
Client: I get a simple component:
RESULT: ConcreteComponent

Client: Now I've got a decorated component:
RESULT: ConcreteDecoratorB(ConcreteDecoratorA(ConcreteComponent))
```

--------------------------------

### Define CarType enumeration

Source: https://refactoringguru.cn/design-patterns/builder/java/example

Defines the available types of cars used within the builder example.

```java
package refactoring_guru.builder.example.cars;

public enum CarType {
    CITY_CAR, SPORTS_CAR, SUV
}
```

--------------------------------

### Execution Output for Template Method Example

Source: https://refactoringguru.cn/design-patterns/template-method/swift/example

Displays the console output generated by the permission accessor implementation.

```text
You have access to Camera

You have access to Microphone

PhotoLibrary Accessor: Rejected with access. Updating analytics...
You do not have access to PhotoLibrary

```

--------------------------------

### Client Code for Builder Pattern

Source: https://refactoringguru.cn/design-patterns/builder/cpp/example

Demonstrates how to use a director to build products and how to manually construct a custom product without a director.

```cpp
void ClientCode(Director& director)
{
    ConcreteBuilder1* builder = new ConcreteBuilder1();
    director.set_builder(builder);
    std::cout << "Standard basic product:\n"; 
    director.BuildMinimalViableProduct();
    
    Product1* p= builder->GetProduct();
    p->ListParts();
    delete p;

    std::cout << "Standard full featured product:\n"; 
    director.BuildFullFeaturedProduct();

    p= builder->GetProduct();
    p->ListParts();
    delete p;

    // Remember, the Builder pattern can be used without a Director class.
    std::cout << "Custom product:\n";
    builder->ProducePartA();
    builder->ProducePartC();
    p=builder->GetProduct();
    p->ListParts();
    delete p;

    delete builder;
}
```

--------------------------------

### Execution Output

Source: https://refactoringguru.cn/design-patterns/proxy/php/example

Shows the console output when running the proxy example, demonstrating cache hits and misses.

```text
Executing client code with real subject:
Downloading a file from the Internet.
Downloaded bytes: 1270
Downloading a file from the Internet.
Downloaded bytes: 1270

Executing the same client code with a proxy:
CacheProxy MISS. Downloading a file from the Internet.
Downloaded bytes: 1270
CacheProxy HIT. Retrieving result from cache.
```

--------------------------------

### Configure and Execute Chain of Responsibility Demo

Source: https://refactoringguru.cn/design-patterns/chain-of-responsibility/java/example

The Demo class initializes the server and links various middleware components to process login requests.

```java
package refactoring_guru.chain_of_responsibility.example;

import refactoring_guru.chain_of_responsibility.example.middleware.Middleware;
import refactoring_guru.chain_of_responsibility.example.middleware.RoleCheckMiddleware;
import refactoring_guru.chain_of_responsibility.example.middleware.ThrottlingMiddleware;
import refactoring_guru.chain_of_responsibility.example.middleware.UserExistsMiddleware;
import refactoring_guru.chain_of_responsibility.example.server.Server;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/**
 * Demo class. Everything comes together here.
 */
public class Demo {
    private static BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    private static Server server;

    private static void init() {
        server = new Server();
        server.register("admin@example.com", "admin_pass");
        server.register("user@example.com", "user_pass");

        // All checks are linked. Client can build various chains using the same
        // components.
        Middleware middleware = Middleware.link(
            new ThrottlingMiddleware(2),
            new UserExistsMiddleware(server),
            new RoleCheckMiddleware()
        );

        // Server gets a chain from client code.
        server.setMiddleware(middleware);
    }

    public static void main(String[] args) throws IOException {
        init();

        boolean success;
        do {
            System.out.print("Enter email: ");
            String email = reader.readLine();
            System.out.print("Input password: ");
            String password = reader.readLine();
            success = server.logIn(email, password);
        } while (!success);
    }
}
```

--------------------------------

### Fluent Interface Example

Source: https://refactoringguru.cn/design-patterns/builder/rust/example

Demonstrates method chaining for object construction, which is distinct from the formal Builder pattern.

```rust
let car = Car::default().places(5).gas(30)
```

--------------------------------

### Execute Proxy Pattern

Source: https://refactoringguru.cn/design-patterns/proxy/rust/example

Main entry point demonstrating the proxy handling requests and enforcing rate limits.

```rust
mod server;

use crate::server::{NginxServer, Server};

fn main() {
    let app_status = &"/app/status".to_string();
    let create_user = &"/create/user".to_string();

    let mut nginx = NginxServer::new();

    let (code, body) = nginx.handle_request(app_status, "GET");
    println!("Url: {}\nHttpCode: {}\nBody: {}\n", app_status, code, body);

    let (code, body) = nginx.handle_request(app_status, "GET");
    println!("Url: {}\nHttpCode: {}\nBody: {}\n", app_status, code, body);

    let (code, body) = nginx.handle_request(app_status, "GET");
    println!("Url: {}\nHttpCode: {}\nBody: {}\n", app_status, code, body);

    let (code, body) = nginx.handle_request(create_user, "POST");
    println!("Url: {}\nHttpCode: {}\nBody: {}\n", create_user, code, body);

    let (code, body) = nginx.handle_request(create_user, "GET");
    println!("Url: {}\nHttpCode: {}\nBody: {}\n", create_user, code, body);
}
```

--------------------------------

### Bridge Pattern Execution Output

Source: https://refactoringguru.cn/design-patterns/bridge/csharp/example

The expected console output when running the conceptual Bridge pattern example.

```text
Abstract: Base operation with:
ConcreteImplementationA: The result in platform A.

ExtendedAbstraction: Extended operation with:
ConcreteImplementationA: The result in platform B.
```

--------------------------------

### Execution Output of Flyweight Example

Source: https://refactoringguru.cn/design-patterns/flyweight/swift/example

Shows the console output verifying that appearance objects are cached and reused after the first creation.

```text
Client: I created a number of objects to display
Client: Let's show animals for the 1st time

AppearanceFactory: Can't find a cached cat-object, creating a new one.
Cell: Updating an appearance of a cat-cell: photos 1

AppearanceFactory: Reusing an existing cat-appearance.
Cell: Updating an appearance of a cat-cell: photos 1

AppearanceFactory: Can't find a cached dog-object, creating a new one.
Cell: Updating an appearance of a dog-cell: photos 2


Client: I have a new dog, let's show it the same way!

AppearanceFactory: Reusing an existing dog-appearance.
Cell: Updating an appearance of a dog-cell: photos 2
```

--------------------------------

### Implement Memento Pattern in C++

Source: https://refactoringguru.cn/design-patterns/memento/cpp/example

This example demonstrates the interaction between the Originator, ConcreteMemento, and Caretaker classes to perform state backups and rollbacks.

```cpp
/**
 * The Memento interface provides a way to retrieve the memento's metadata, such
 * as creation date or name. However, it doesn't expose the Originator's state.
 */
class Memento {
 public:
  virtual ~Memento() {}
  virtual std::string GetName() const = 0;
  virtual std::string date() const = 0;
  virtual std::string state() const = 0;
};

/**
 * The Concrete Memento contains the infrastructure for storing the Originator's
 * state.
 */
class ConcreteMemento : public Memento {
 private:
  std::string state_;
  std::string date_;

 public:
  ConcreteMemento(std::string state) : state_(state) {
    this->state_ = state;
    std::time_t now = std::time(0);
    this->date_ = std::ctime(&now);
  }
  /**
   * The Originator uses this method when restoring its state.
   */
  std::string state() const override {
    return this->state_;
  }
  /**
   * The rest of the methods are used by the Caretaker to display metadata.
   */
  std::string GetName() const override {
    return this->date_ + " / (" + this->state_.substr(0, 9) + "...)";
  }
  std::string date() const override {
    return this->date_;
  }
};

/**
 * The Originator holds some important state that may change over time. It also
 * defines a method for saving the state inside a memento and another method for
 * restoring the state from it.
 */
class Originator {
  /**
   * @var string For the sake of simplicity, the originator's state is stored
   * inside a single variable.
   */
 private:
  std::string state_;

  std::string GenerateRandomString(int length = 10) {
    const char alphanum[] =
        "0123456789"
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        "abcdefghijklmnopqrstuvwxyz";
    int stringLength = sizeof(alphanum) - 1;

    std::string random_string;
    for (int i = 0; i < length; i++) {
      random_string += alphanum[std::rand() % stringLength];
    }
    return random_string;
  }

 public:
  Originator(std::string state) : state_(state) {
    std::cout << "Originator: My initial state is: " << this->state_ << "\n";
  }
  /**
   * The Originator's business logic may affect its internal state. Therefore,
   * the client should backup the state before launching methods of the business
   * logic via the save() method.
   */
  void DoSomething() {
    std::cout << "Originator: I'm doing something important.\n";
    this->state_ = this->GenerateRandomString(30);
    std::cout << "Originator: and my state has changed to: " << this->state_ << "\n";
  }

  /**
   * Saves the current state inside a memento.
   */
  Memento *Save() {
    return new ConcreteMemento(this->state_);
  }
  /**
   * Restores the Originator's state from a memento object.
   */
  void Restore(Memento *memento) {
    this->state_ = memento->state();
    std::cout << "Originator: My state has changed to: " << this->state_ << "\n";
    delete memento;
  }
};

/**
 * The Caretaker doesn't depend on the Concrete Memento class. Therefore, it
 * doesn't have access to the originator's state, stored inside the memento. It
 * works with all mementos via the base Memento interface.
 */
class Caretaker {
  /**
   * @var Memento[]
   */
 private:
  std::vector<Memento *> mementos_;

  /**
   * @var Originator
   */
  Originator *originator_;

 public:
     Caretaker(Originator* originator) : originator_(originator) {
     }

     ~Caretaker() {
         for (auto m : mementos_) delete m;
     }

  void Backup() {
    std::cout << "\nCaretaker: Saving Originator's state...\n";
    this->mementos_.push_back(this->originator_->Save());
  }
  void Undo() {
    if (!this->mementos_.size()) {
      return;
    }
    Memento *memento = this->mementos_.back();
    this->mementos_.pop_back();
    std::cout << "Caretaker: Restoring state to: " << memento->GetName() << "\n";
    try {
      this->originator_->Restore(memento);
    } catch (...) {
      this->Undo();
    }
  }
  void ShowHistory() const {
    std::cout << "Caretaker: Here's the list of mementos:\n";
    for (Memento *memento : this->mementos_) {
      std::cout << memento->GetName() << "\n";
    }
  }
};
/**
 * Client code.
 */

void ClientCode() {
  Originator *originator = new Originator("Super-duper-super-puper-super.");
  Caretaker *caretaker = new Caretaker(originator);
  caretaker->Backup();
  originator->DoSomething();
  caretaker->Backup();
  originator->DoSomething();
  caretaker->Backup();
  originator->DoSomething();
  std::cout << "\n";
  caretaker->ShowHistory();
  std::cout << "\nClient: Now, let's rollback!\n\n";
  caretaker->Undo();
  std::cout << "\nClient: Once more!\n\n";
  caretaker->Undo();

  delete originator;
  delete caretaker;
}

int main() {
  std::srand(static_cast<unsigned int>(std::time(NULL)));
  ClientCode();
  return 0;
}
```

--------------------------------

### Implement Client Demo for Strategy Pattern

Source: https://refactoringguru.cn/design-patterns/strategy/java/example

The Demo class acts as the client, selecting a concrete payment strategy at runtime based on user input and executing the order process.

```java
package refactoring_guru.strategy.example;

import refactoring_guru.strategy.example.order.Order;
import refactoring_guru.strategy.example.strategies.PayByCreditCard;
import refactoring_guru.strategy.example.strategies.PayByPayPal;
import refactoring_guru.strategy.example.strategies.PayStrategy;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;

/**
 * World first console e-commerce application.
 */
public class Demo {
    private static Map<Integer, Integer> priceOnProducts = new HashMap<>();
    private static BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    private static Order order = new Order();
    private static PayStrategy strategy;

    static {
        priceOnProducts.put(1, 2200);
        priceOnProducts.put(2, 1850);
        priceOnProducts.put(3, 1100);
        priceOnProducts.put(4, 890);
    }

    public static void main(String[] args) throws IOException {
        while (!order.isClosed()) {
            int cost;

            String continueChoice;
            do {
                System.out.print("Please, select a product:" + "\n" +
                        "1 - Mother board" + "\n" +
                        "2 - CPU" + "\n" +
                        "3 - HDD" + "\n" +
                        "4 - Memory" + "\n");
                int choice = Integer.parseInt(reader.readLine());
                cost = priceOnProducts.get(choice);
                System.out.print("Count: ");
                int count = Integer.parseInt(reader.readLine());
                order.setTotalCost(cost * count);
                System.out.print("Do you wish to continue selecting products? Y/N: ");
                continueChoice = reader.readLine();
            } while (continueChoice.equalsIgnoreCase("Y"));

            if (strategy == null) {
                System.out.println("Please, select a payment method:" + "\n" +
                        "1 - PalPay" + "\n" +
                        "2 - Credit Card");
                String paymentMethod = reader.readLine();

                // Client creates different strategies based on input from user,
                // application configuration, etc.
                if (paymentMethod.equals("1")) {
                    strategy = new PayByPayPal();
                } else {
                    strategy = new PayByCreditCard();
                }
            }

            // Order object delegates gathering payment data to strategy object,
            // since only strategies know what data they need to process a
            // payment.
            order.processOrder(strategy);

            System.out.print("Pay " + order.getTotalCost() + " units or Continue shopping? P/C: ");
            String proceed = reader.readLine();
            if (proceed.equalsIgnoreCase("P")) {
                // Finally, strategy handles the payment.
                if (strategy.pay(order.getTotalCost())) {
                    System.out.println("Payment has been successful.");
                } else {
                    System.out.println("FAIL! Please, check your data.");
                }
                order.setClosed();
            }
        }
    }
}
```

--------------------------------

### Flyweight Pattern Conceptual Implementation in C#

Source: https://refactoringguru.cn/design-patterns/flyweight/csharp/example

This example demonstrates the Flyweight, FlyweightFactory, and Car classes. It requires the Json.NET library for serialization.

```csharp
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.Json;
// Use Json.NET library, you can download it from NuGet Package Manager

namespace RefactoringGuru.DesignPatterns.Flyweight.Conceptual
{
    // The Flyweight stores a common portion of the state (also called intrinsic
    // state) that belongs to multiple real business entities. The Flyweight
    // accepts the rest of the state (extrinsic state, unique for each entity)
    // via its method parameters.
    public class Flyweight
    {
        private Car _sharedState;

        public Flyweight(Car car)
        {
            this._sharedState = car;
        }

        public void Operation(Car uniqueState)
        {
            string s = JsonSerializer.Serialize(this._sharedState);
            string u = JsonSerializer.Serialize(uniqueState);
            Console.WriteLine($"Flyweight: Displaying shared {s} and unique {u} state.");
        }
    }

    // The Flyweight Factory creates and manages the Flyweight objects. It
    // ensures that flyweights are shared correctly. When the client requests a
    // flyweight, the factory either returns an existing instance or creates a
    // new one, if it doesn't exist yet.
    public class FlyweightFactory
    {
        private List<Tuple<Flyweight, string>> flyweights = new List<Tuple<Flyweight, string>>();

        public FlyweightFactory(params Car[] args)
        {
            foreach (var elem in args)
            {
                flyweights.Add(new Tuple<Flyweight, string>(new Flyweight(elem), this.getKey(elem)));
            }
        }

        // Returns a Flyweight's string hash for a given state.
        public string getKey(Car key)
        {
            List<string> elements = new List<string>();

            elements.Add(key.Model);
            elements.Add(key.Color);
            elements.Add(key.Company);

            if (key.Owner != null && key.Number != null)
            {
                elements.Add(key.Number);
                elements.Add(key.Owner);
            }

            elements.Sort();

            return string.Join("_", elements);
        }

        // Returns an existing Flyweight with a given state or creates a new
        // one.
        public Flyweight GetFlyweight(Car sharedState)
        {
            string key = this.getKey(sharedState);

            if (flyweights.Where(t => t.Item2 == key).Count() == 0)
            {
                Console.WriteLine("FlyweightFactory: Can't find a flyweight, creating new one.");
                this.flyweights.Add(new Tuple<Flyweight, string>(new Flyweight(sharedState), key));
            }
            else
            {
                Console.WriteLine("FlyweightFactory: Reusing existing flyweight.");
            }
            return this.flyweights.Where(t => t.Item2 == key).FirstOrDefault().Item1;
        }

        public void listFlyweights()
        {
            var count = flyweights.Count;
            Console.WriteLine($"\nFlyweightFactory: I have {count} flyweights:");
            foreach (var flyweight in flyweights)
            {
                Console.WriteLine(flyweight.Item2);
            }
        }
    }

    public class Car
    {
        public string Owner { get; set; }

        public string Number { get; set; }

        public string Company { get; set; }

        public string Model { get; set; }

        public string Color { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            // The client code usually creates a bunch of pre-populated
            // flyweights in the initialization stage of the application.
            var factory = new FlyweightFactory(
                new Car { Company = "Chevrolet", Model = "Camaro2018", Color = "pink" },
                new Car { Company = "Mercedes Benz", Model = "C300", Color = "black" },
                new Car { Company = "Mercedes Benz", Model = "C500", Color = "red" },
                new Car { Company = "BMW", Model = "M5", Color = "red" },
                new Car { Company = "BMW", Model = "X6", Color = "white" }
            );
            factory.listFlyweights();

            addCarToPoliceDatabase(factory, new Car {
                Number = "CL234IR",
                Owner = "James Doe",
                Company = "BMW",
                Model = "M5",
                Color = "red"
            });
```

--------------------------------

### Builder Pattern Client Implementation in C#

Source: https://refactoringguru.cn/design-patterns/builder/csharp/example

Demonstrates how to use a Director to build products or construct them manually using the builder instance.

```csharp
class Program
    {
        static void Main(string[] args)
        {
            // The client code creates a builder object, passes it to the
            // director and then initiates the construction process. The end
            // result is retrieved from the builder object.
            var director = new Director();
            var builder = new ConcreteBuilder();
            director.Builder = builder;
            
            Console.WriteLine("Standard basic product:");
            director.BuildMinimalViableProduct();
            Console.WriteLine(builder.GetProduct().ListParts());

            Console.WriteLine("Standard full featured product:");
            director.BuildFullFeaturedProduct();
            Console.WriteLine(builder.GetProduct().ListParts());

            // Remember, the Builder pattern can be used without a Director
            // class.
            Console.WriteLine("Custom product:");
            builder.BuildPartA();
            builder.BuildPartC();
            Console.Write(builder.GetProduct().ListParts());
        }
    }
```

--------------------------------

### View Execution Output

Source: https://refactoringguru.cn/design-patterns/chain-of-responsibility/java/example

Sample output demonstrating the behavior of the middleware chain during login attempts.

```text
Enter email: admin@example.com
Input password: admin_pass
Hello, admin!
Authorization have been successful!


Enter email: wrong@example.com
Input password: wrong_pass
This email is not registered!
Enter email: wrong@example.com
Input password: wrong_pass
This email is not registered!
Enter email: wrong@example.com
Input password: wrong_pass
Request limit exceeded!
```

--------------------------------

### Mediator Pattern Implementation in Swift

Source: https://refactoringguru.cn/design-patterns/mediator/swift/example

This example defines a ScreenMediator that implements the ScreenUpdatable protocol to broadcast news updates to registered view controllers.

```swift
import XCTest

class MediatorRealWorld: XCTestCase {

    func test() {

        let newsArray = [News(id: 1, title: "News1", likesCount: 1),
                         News(id: 2, title: "News2", likesCount: 2)]

        let numberOfGivenLikes = newsArray.reduce(0, { $0 + $1.likesCount })

        let mediator = ScreenMediator()

        let feedVC = NewsFeedViewController(mediator, newsArray)
        let newsDetailVC = NewsDetailViewController(mediator, newsArray.first!)
        let profileVC = ProfileViewController(mediator, numberOfGivenLikes)

        mediator.update([feedVC, newsDetailVC, profileVC])

        feedVC.userLikedAllNews()
        feedVC.userDislikedAllNews()
    }
}

class NewsFeedViewController: ScreenUpdatable {

    private var newsArray: [News]
    private weak var mediator: ScreenUpdatable?

    init(_ mediator: ScreenUpdatable?, _ newsArray: [News]) {
        self.newsArray = newsArray
        self.mediator = mediator
    }

    func likeAdded(to news: News) {

        print("News Feed: Received a liked news model with id \(news.id)")

        for var item in newsArray {
            if item == news {
                item.likesCount += 1
            }
        }
    }

    func likeRemoved(from news: News) {

        print("News Feed: Received a disliked news model with id \(news.id)")

        for var item in newsArray {
            if item == news {
                item.likesCount -= 1
            }
        }
    }

    func userLikedAllNews() {
        print("\n\nNews Feed: User LIKED all news models")
        print("News Feed: I am telling to mediator about it...\n")
        newsArray.forEach({ mediator?.likeAdded(to: $0) })
    }

    func userDislikedAllNews() {
        print("\n\nNews Feed: User DISLIKED all news models")
        print("News Feed: I am telling to mediator about it...\n")
        newsArray.forEach({ mediator?.likeRemoved(from: $0) })
    }
}

class NewsDetailViewController: ScreenUpdatable {

    private var news: News
    private weak var mediator: ScreenUpdatable?

    init(_ mediator: ScreenUpdatable?, _ news: News) {
        self.news = news
        self.mediator = mediator
    }

    func likeAdded(to news: News) {
        print("News Detail: Received a liked news model with id \(news.id)")
        if self.news == news {
            self.news.likesCount += 1
        }
    }

    func likeRemoved(from news: News) {
        print("News Detail: Received a disliked news model with id \(news.id)")
        if self.news == news {
            self.news.likesCount -= 1
        }
    }
}

class ProfileViewController: ScreenUpdatable {

    private var numberOfGivenLikes: Int
    private weak var mediator: ScreenUpdatable?

    init(_ mediator: ScreenUpdatable?, _ numberOfGivenLikes: Int) {
        self.numberOfGivenLikes = numberOfGivenLikes
        self.mediator = mediator
    }

    func likeAdded(to news: News) {
        print("Profile: Received a liked news model with id \(news.id)")
        numberOfGivenLikes += 1
    }

    func likeRemoved(from news: News) {
        print("Profile: Received a disliked news model with id \(news.id)")
        numberOfGivenLikes -= 1
    }
}

protocol ScreenUpdatable: class {

    func likeAdded(to news: News)

    func likeRemoved(from news: News)
}

class ScreenMediator: ScreenUpdatable {

    private var screens: [ScreenUpdatable]?

    func update(_ screens: [ScreenUpdatable]) {
        self.screens = screens
    }

    func likeAdded(to news: News) {
        print("Screen Mediator: Received a liked news model with id \(news.id)")
        screens?.forEach({ $0.likeAdded(to: news) })
    }

    func likeRemoved(from news: News) {
        print("ScreenMediator: Received a disliked news model with id \(news.id)")
        screens?.forEach({ $0.likeRemoved(from: news) })
    }
}

struct News: Equatable {

    let id: Int

    let title: String

    var likesCount: Int

    /// Other properties

    static func == (left: News, right: News) -> Bool {
        return left.id == right.id
    }
}
```

--------------------------------

### 实现责任链模式 (main.py)

Source: https://refactoringguru.cn/design-patterns/chain-of-responsibility/python/example

定义抽象处理者接口及具体处理者类，通过 set_next 方法构建处理链。

```python
from __future__ import annotations
from abc import ABC, abstractmethod
from typing import Any, Optional


class Handler(ABC):
    """
    The Handler interface declares a method for building the chain of handlers.
    It also declares a method for executing a request.
    """

    @abstractmethod
    def set_next(self, handler: Handler) -> Handler:
        pass

    @abstractmethod
    def handle(self, request) -> Optional[str]:
        pass


class AbstractHandler(Handler):
    """
    The default chaining behavior can be implemented inside a base handler
    class.
    """

    _next_handler: Handler = None

    def set_next(self, handler: Handler) -> Handler:
        self._next_handler = handler
        # Returning a handler from here will let us link handlers in a
        # convenient way like this:
        # monkey.set_next(squirrel).set_next(dog)
        return handler

    @abstractmethod
    def handle(self, request: Any) -> str:
        if self._next_handler:
            return self._next_handler.handle(request)

        return None


"""
All Concrete Handlers either handle a request or pass it to the next handler in
the chain.
"""


class MonkeyHandler(AbstractHandler):
    def handle(self, request: Any) -> str:
        if request == "Banana":
            return f"Monkey: I'll eat the {request}"
        else:
            return super().handle(request)


class SquirrelHandler(AbstractHandler):
    def handle(self, request: Any) -> str:
        if request == "Nut":
            return f"Squirrel: I'll eat the {request}"
        else:
            return super().handle(request)


class DogHandler(AbstractHandler):
    def handle(self, request: Any) -> str:
        if request == "MeatBall":
            return f"Dog: I'll eat the {request}"
        else:
            return super().handle(request)


def client_code(handler: Handler) -> None:
    """
    The client code is usually suited to work with a single handler. In most
    cases, it is not even aware that the handler is part of a chain.
    """

    for food in ["Nut", "Banana", "Cup of coffee"]:
        print(f"\nClient: Who wants a {food}?")
        result = handler.handle(food)
        if result:
            print(f"  {result}", end="")
        else:
            print(f"  {food} was left untouched.", end="")


if __name__ == "__main__":
    monkey = MonkeyHandler()
    squirrel = SquirrelHandler()
    dog = DogHandler()

    monkey.set_next(squirrel).set_next(dog)

    # The client should be able to send a request to any handler, not just the
    # first one in the chain.
    print("Chain: Monkey > Squirrel > Dog")
    client_code(monkey)
    print("\n")

    print("Subchain: Squirrel > Dog")
    client_code(squirrel)
```

--------------------------------

### Execute Bridge Pattern Demo

Source: https://refactoringguru.cn/design-patterns/bridge/java/example

The Demo class initializes devices and remotes to demonstrate the interaction between abstractions and implementations.

```java
package refactoring_guru.bridge.example;

import refactoring_guru.bridge.example.devices.Device;
import refactoring_guru.bridge.example.devices.Radio;
import refactoring_guru.bridge.example.devices.Tv;
import refactoring_guru.bridge.example.remotes.AdvancedRemote;
import refactoring_guru.bridge.example.remotes.BasicRemote;

public class Demo {
    public static void main(String[] args) {
        testDevice(new Tv());
        testDevice(new Radio());
    }

    public static void testDevice(Device device) {
        System.out.println("Tests with basic remote.");
        BasicRemote basicRemote = new BasicRemote(device);
        basicRemote.power();
        device.printStatus();

        System.out.println("Tests with advanced remote.");
        AdvancedRemote advancedRemote = new AdvancedRemote(device);
        advancedRemote.power();
        advancedRemote.mute();
        device.printStatus();
    }
}
```
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