PHPで大規模システムを構築するためのデザインパターン活用ガイド

// 製品クラス
interface DatabaseConnection {
    public function connect();
}

class MySQLConnection implements DatabaseConnection {
    public function connect() {
        echo "Connecting to MySQL";
    }
}

class PostgreSQLConnection implements DatabaseConnection {
    public function connect() {
        echo "Connecting to PostgreSQL";
    }
}

// ファクトリクラス
class DatabaseConnectionFactory {
    public static function createConnection($type) {
        switch ($type) {
            case 'mysql':
                return new MySQLConnection();
            case 'pgsql':
                return new PostgreSQLConnection();
            default:
                throw new Exception("Invalid database type");
        }
    }
}

// 使用例
$db = DatabaseConnectionFactory::createConnection('mysql');
$db->connect();

class DatabaseConnection {
    private static $instance = null;
    private $connection;

    private function __construct() {
        $this->connection = new PDO('mysql:host=localhost;dbname=testdb', 'user', 'password');
    }

    public static function getInstance() {
        if (self::$instance === null) {
            self::$instance = new DatabaseConnection();
        }
        return self::$instance;
    }

    public function getConnection() {
        return $this->connection;
    }
}

// 使用例
$dbConnection = DatabaseConnection::getInstance()->getConnection();

// ストラテジーインターフェース
interface TaxStrategy {
    public function calculate($amount);
}

// 具体的なストラテジークラス
class StandardTax implements TaxStrategy {
    public function calculate($amount) {
        return $amount * 0.1; // 10%の税率
    }
}

class ReducedTax implements TaxStrategy {
    public function calculate($amount) {
        return $amount * 0.05; // 5%の税率
    }
}

// コンテキストクラス
class TaxCalculator {
    private $strategy;

    public function __construct(TaxStrategy $strategy) {
        $this->strategy = $strategy;
    }

    public function calculateTax($amount) {
        return $this->strategy->calculate($amount);
    }
}

// 使用例
$calculator = new TaxCalculator(new StandardTax());
echo $calculator->calculateTax(1000); // 標準税率での計算
$calculator = new TaxCalculator(new ReducedTax());
echo $calculator->calculateTax(1000); // 割引税率での計算

// オブザーバーインターフェース
interface Observer {
    public function update($eventData);
}

// 具体的なオブザーバークラス
class EmailNotifier implements Observer {
    public function update($eventData) {
        echo "Sending email to " . $eventData['user'];
    }
}

class Logger implements Observer {
    public function update($eventData) {
        echo "Logging event for " . $eventData['user'];
    }
}

// サブジェクトクラス
class UserLogin {
    private $observers = [];

    public function addObserver(Observer $observer) {
        $this->observers[] = $observer;
    }

    public function notifyObservers($eventData) {
        foreach ($this->observers as $observer) {
            $observer->update($eventData);
        }
    }

    public function login($user) {
        // ログイン処理
        echo "User $user has logged in.\n";

        // オブザーバーに通知
        $this->notifyObservers(['user' => $user]);
    }
}

// 使用例
$loginSystem = new UserLogin();
$loginSystem->addObserver(new EmailNotifier());
$loginSystem->addObserver(new Logger());

$loginSystem->login("Alice");

// コンポーネントインターフェース
interface Message {
    public function send($content);
}

// 基本のメッセージクラス
class BasicMessage implements Message {
    public function send($content) {
        echo "Sending message: $content";
    }
}

// デコレーターの抽象クラス
abstract class MessageDecorator implements Message {
    protected $message;

    public function __construct(Message $message) {
        $this->message = $message;
    }

    public function send($content) {
        $this->message->send($content);
    }
}

// 具体的なデコレータークラス：暗号化
class EncryptedMessage extends MessageDecorator {
    public function send($content) {
        $content = "Encrypted(" . $content . ")";
        parent::send($content);
    }
}

// 具体的なデコレータークラス：ログ記録
class LoggedMessage extends MessageDecorator {
    public function send($content) {
        echo "Logging message.\n";
        parent::send($content);
    }
}

// 使用例
$message = new LoggedMessage(new EncryptedMessage(new BasicMessage()));
$message->send("Hello, World!");

// コンポーネントインターフェース
interface FileSystemComponent {
    public function show();
}

// リーフクラス：ファイル
class File implements FileSystemComponent {
    private $name;

    public function __construct($name) {
        $this->name = $name;
    }

    public function show() {
        echo "File: " . $this->name . "\n";
    }
}

// コンポジットクラス：フォルダ
class Folder implements FileSystemComponent {
    private $name;
    private $children = [];

    public function __construct($name) {
        $this->name = $name;
    }

    public function add(FileSystemComponent $component) {
        $this->children[] = $component;
    }

    public function show() {
        echo "Folder: " . $this->name . "\n";
        foreach ($this->children as $child) {
            $child->show();
        }
    }
}

// 使用例
$rootFolder = new Folder("Root");
$file1 = new File("File1.txt");
$file2 = new File("File2.txt");
$subFolder = new Folder("SubFolder");
$file3 = new File("File3.txt");

$rootFolder->add($file1);
$rootFolder->add($file2);
$subFolder->add($file3);
$rootFolder->add($subFolder);

$rootFolder->show();

interface Notification {
    public function send($message);
}

class EmailNotification implements Notification {
    public function send($message) {
        echo "Sending email: $message\n";
    }
}

class SmsNotification implements Notification {
    public function send($message) {
        echo "Sending SMS: $message\n";
    }
}

class NotificationFactory {
    public static function createNotification($type) {
        switch ($type) {
            case 'email':
                return new EmailNotification();
            case 'sms':
                return new SmsNotification();
            default:
                throw new Exception("Invalid notification type");
        }
    }
}

class DatabaseConnection {
    private static $instance = null;
    private $connection;

    private function __construct() {
        $this->connection = new PDO('mysql:host=localhost;dbname=shop', 'user', 'password');
    }

    public static function getInstance() {
        if (self::$instance === null) {
            self::$instance = new DatabaseConnection();
        }
        return self::$instance;
    }

    public function getConnection() {
        return $this->connection;
    }
}

interface Observer {
    public function update($orderData);
}

class OrderNotifier implements Observer {
    public function update($orderData) {
        echo "Notifying order completion for order #" . $orderData['id'] . "\n";
    }
}

class Order {
    private $observers = [];

    public function addObserver(Observer $observer) {
        $this->observers[] = $observer;
    }

    public function notifyObservers($orderData) {
        foreach ($this->observers as $observer) {
            $observer->update($orderData);
        }
    }

    public function completeOrder($orderData) {
        echo "Order #" . $orderData['id'] . " is completed.\n";
        $this->notifyObservers($orderData);
    }
}

// 使用例
$orderSystem = new Order();
$orderSystem->addObserver(new OrderNotifier());
$orderSystem->completeOrder(['id' => 123]);

class ServiceFactory {
    private static $services = [];

    public static function getService($type) {
        if (!isset(self::$services[$type])) {
            switch ($type) {
                case 'database':
                    self::$services[$type] = DatabaseConnection::getInstance();
                    break;
                case 'email':
                    self::$services[$type] = new EmailNotification();
                    break;
                // 他のサービスも追加可能
                default:
                    throw new Exception("Unknown service type");
            }
        }
        return self::$services[$type];
    }
}

// 使用例
$dbService = ServiceFactory::getService('database');
$emailService = ServiceFactory::getService('email');

interface DiscountStrategy {
    public function apply($amount);
}

class SeasonalDiscount implements DiscountStrategy {
    public function apply($amount) {
        return $amount * 0.9; // 10%割引
    }
}

class MemberDiscount implements DiscountStrategy {
    public function apply($amount) {
        return $amount * 0.85; // 15%割引
    }
}

abstract class DiscountDecorator implements DiscountStrategy {
    protected $strategy;

    public function __construct(DiscountStrategy $strategy) {
        $this->strategy = $strategy;
    }

    public function apply($amount) {
        return $this->strategy->apply($amount);
    }
}

class ExtraGiftDiscount extends DiscountDecorator {
    public function apply($amount) {
        $amount = parent::apply($amount);
        echo "Applying extra gift with purchase.\n";
        return $amount;
    }
}

// 使用例
$discount = new ExtraGiftDiscount(new SeasonalDiscount());
$total = $discount->apply(1000); // 合計金額の割引適用

// オブザーバーは前の例と同様
class NotificationManager {
    private $observers = [];

    public function addObserver(Observer $observer) {
        $this->observers[] = $observer;
    }

    public function notifyAll($eventData) {
        foreach ($this->observers as $observer) {
            $observer->update($eventData);
        }
    }

    public function notifyEvent($type, $message) {
        $notification = NotificationFactory::createNotification($type);
        foreach ($this->observers as $observer) {
            $notification->send($message);
        }
    }
}