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--- development:software-architecture:design-patterns:chain-of-responsibility [2024/08/23 04:51] – tungnt
+++ development:software-architecture:design-patterns:chain-of-responsibility [2024/08/24 03:28] (current) – tungnt
@@ Line 3: / Line 3: @@
 https://refactoring.guru/design-patterns/chain-of-responsibility
+{{ :development:software-architecture:design-patterns:chain-of-responsibility.png |}}
+{{ :development:software-architecture:design-patterns:solution1-en.png |}}
+**Ví dụ 1:**
+<file php>
+<?php
+namespace RefactoringGuru\ChainOfResponsibility\Conceptual;
+/**
+ * The Handler interface declares a method for building the chain of handlers.
+ * It also declares a method for executing a request.
+ */
+interface Handler
+{
+    public function setNext(Handler $handler): Handler;
+    public function handle(string $request): ?string;
+}
+/**
+ * The default chaining behavior can be implemented inside a base handler class.
+ */
+abstract class AbstractHandler implements Handler
+{
+    /**
+     * @var Handler
+     */
+    private $nextHandler;
+    public function setNext(Handler $handler): Handler
+    {
+        $this->nextHandler = $handler;
+        // Returning a handler from here will let us link handlers in a
+        // convenient way like this:
+        // $monkey->setNext($squirrel)->setNext($dog);
+        return $handler;
+    }
+    public function handle(string $request): ?string
+    {
+        if ($this->nextHandler) {
+            return $this->nextHandler->handle($request);
+        }
+        return null;
+    }
+}
+/**
+ * All Concrete Handlers either handle a request or pass it to the next handler
+ * in the chain.
+ */
+class MonkeyHandler extends AbstractHandler
+{
+    public function handle(string $request): ?string
+    {
+        if ($request === "Banana") {
+            return "Monkey: I'll eat the " . $request . ".\n";
+        } else {
+            return parent::handle($request);
+        }
+    }
+}
+class SquirrelHandler extends AbstractHandler
+{
+    public function handle(string $request): ?string
+    {
+        if ($request === "Nut") {
+            return "Squirrel: I'll eat the " . $request . ".\n";
+        } else {
+            return parent::handle($request);
+        }
+    }
+}
+class DogHandler extends AbstractHandler
+{
+    public function handle(string $request): ?string
+    {
+        if ($request === "MeatBall") {
+            return "Dog: I'll eat the " . $request . ".\n";
+        } else {
+            return parent::handle($request);
+        }
+    }
+}
+/**
+ * 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.
+ */
+function clientCode(Handler $handler)
+{
+    foreach (["Nut", "Banana", "Cup of coffee"] as $food) {
+        echo "Client: Who wants a " . $food . "?\n";
+        $result = $handler->handle($food);
+        if ($result) {
+            echo "  " . $result;
+        } else {
+            echo "  " . $food . " was left untouched.\n";
+        }
+    }
+}
+/**
+ * The other part of the client code constructs the actual chain.
+ */
+$monkey = new MonkeyHandler();
+$squirrel = new SquirrelHandler();
+$dog = new DogHandler();
+$monkey->setNext($squirrel)->setNext($dog);
+/**
+ * The client should be able to send a request to any handler, not just the
+ * first one in the chain.
+ */
+echo "Chain: Monkey > Squirrel > Dog\n\n";
+clientCode($monkey);
+echo "\n";
+echo "Subchain: Squirrel > Dog\n\n";
+clientCode($squirrel);
+</file>
+**Ví dụ 2:**
+<file php>
+<?php
+namespace RefactoringGuru\ChainOfResponsibility\RealWorld;
+/**
+ * The classic CoR pattern declares a single role for objects that make up a
+ * chain, which is a Handler. In our example, let's differentiate between
+ * middleware and a final application's handler, which is executed when a
+ * request gets through all the middleware objects.
+ *
+ * The base Middleware class declares an interface for linking middleware
+ * objects into a chain.
+ */
+abstract class Middleware
+{
+    /**
+     * @var Middleware
+     */
+    private $next;
+    /**
+     * This method can be used to build a chain of middleware objects.
+     */
+    public function linkWith(Middleware $next): Middleware
+    {
+        $this->next = $next;
+        return $next;
+    }
+    /**
+     * Subclasses must override this method to provide their own checks. A
+     * subclass can fall back to the parent implementation if it can't process a
+     * request.
+     */
+    public function check(string $email, string $password): bool
+    {
+        if (!$this->next) {
+            return true;
+        }
+        return $this->next->check($email, $password);
+    }
+}
+/**
+ * This Concrete Middleware checks whether a user with given credentials exists.
+ */
+class UserExistsMiddleware extends Middleware
+{
+    private $server;
+    public function __construct(Server $server)
+    {
+        $this->server = $server;
+    }
+    public function check(string $email, string $password): bool
+    {
+        if (!$this->server->hasEmail($email)) {
+            echo "UserExistsMiddleware: This email is not registered!\n";
+            return false;
+        }
+        if (!$this->server->isValidPassword($email, $password)) {
+            echo "UserExistsMiddleware: Wrong password!\n";
+            return false;
+        }
+        return parent::check($email, $password);
+    }
+}
+/**
+ * This Concrete Middleware checks whether a user associated with the request
+ * has sufficient permissions.
+ */
+class RoleCheckMiddleware extends Middleware
+{
+    public function check(string $email, string $password): bool
+    {
+        if ($email === "admin@example.com") {
+            echo "RoleCheckMiddleware: Hello, admin!\n";
+            return true;
+        }
+        echo "RoleCheckMiddleware: Hello, user!\n";
+        return parent::check($email, $password);
+    }
+}
+/**
+ * This Concrete Middleware checks whether there are too many failed login
+ * requests.
+ */
+class ThrottlingMiddleware extends Middleware
+{
+    private $requestPerMinute;
+    private $request;
+    private $currentTime;
+    public function __construct(int $requestPerMinute)
+    {
+        $this->requestPerMinute = $requestPerMinute;
+        $this->currentTime = time();
+    }
+    /**
+     * Please, note that the parent::check call can be inserted both at the
+     * beginning of this method and at the end.
+     *
+     * This gives much more flexibility than a simple loop over all middleware
+     * objects. For instance, a middleware can change the order of checks by
+     * running its check after all the others.
+     */
+    public function check(string $email, string $password): bool
+    {
+        if (time() > $this->currentTime + 60) {
+            $this->request = 0;
+            $this->currentTime = time();
+        }
+        $this->request++;
+        if ($this->request > $this->requestPerMinute) {
+            echo "ThrottlingMiddleware: Request limit exceeded!\n";
+            die();
+        }
+        return parent::check($email, $password);
+    }
+}
+/**
+ * This is an application's class that acts as a real handler. The Server class
+ * uses the CoR pattern to execute a set of various authentication middleware
+ * before launching some business logic associated with a request.
+ */
+class Server
+{
+    private $users = [];
+    /**
+     * @var Middleware
+     */
+    private $middleware;
+    /**
+     * The client can configure the server with a chain of middleware objects.
+     */
+    public function setMiddleware(Middleware $middleware): void
+    {
+        $this->middleware = $middleware;
+    }
+    /**
+     * The server gets the email and password from the client and sends the
+     * authorization request to the middleware.
+     */
+    public function logIn(string $email, string $password): bool
+    {
+        if ($this->middleware->check($email, $password)) {
+            echo "Server: Authorization has been successful!\n";
+            // Do something useful for authorized users.
+            return true;
+        }
+        return false;
+    }
+    public function register(string $email, string $password): void
+    {
+        $this->users[$email] = $password;
+    }
+    public function hasEmail(string $email): bool
+    {
+        return isset($this->users[$email]);
+    }
+    public function isValidPassword(string $email, string $password): bool
+    {
+        return $this->users[$email] === $password;
+    }
+}
+/**
+ * The client code.
+ */
+$server = new Server();
+$server->register("admin@example.com", "admin_pass");
+$server->register("user@example.com", "user_pass");
+// All middleware are chained. The client can build various configurations of
+// chains depending on its needs.
+$middleware = new ThrottlingMiddleware(2);
+$middleware
+    ->linkWith(new UserExistsMiddleware($server))
+    ->linkWith(new RoleCheckMiddleware());
+// The server gets a chain from the client code.
+$server->setMiddleware($middleware);
+// ...
+do {
+    echo "\nEnter your email:\n";
+    $email = readline();
+    echo "Enter your password:\n";
+    $password = readline();
+    $success = $server->logIn($email, $password);
+} while (!$success);
+</file>