✅ Add Proxy pattern

README.md

@@ -34,3 +34,4 @@ How to dev:
    8. Facade
    9. Fluent Interface
    10. Flyweight
+   11. Proxy

src/Patterns/Structural/Proxy/BankAccount.php

@@ -0,0 +1,11 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Twent\DesignPatterns\Structural\Proxy;
+
+interface BankAccount
+{
+    public function deposit(int $amount);
+    public function getBalance(): int;
+}

src/Patterns/Structural/Proxy/BankAccountProxy.php

@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Twent\DesignPatterns\Structural\Proxy;
+
+final class BankAccountProxy extends HeavyBankAccount implements BankAccount
+{
+    private ?int $balance = null;
+
+    public function getBalance(): int
+    {
+        if (! $this->balance) {
+            // Call heavy operations
+            $this->balance = parent::getBalance();
+        }
+
+        return $this->balance;
+    }
+}

src/Patterns/Structural/Proxy/HeavyBankAccount.php

@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Twent\DesignPatterns\Structural\Proxy;
+
+class HeavyBankAccount implements BankAccount
+{
+    private array $transactions = [];
+
+    public function deposit(int $amount)
+    {
+        $this->transactions[] = $amount;
+    }
+
+    public function getBalance(): int
+    {
+        // Здесь ресурсоёмкие расчёты, "дорогое" взаимодействие с БД и т.д.
+        return array_sum($this->transactions);
+    }
+}

tests/Feature/Structural/ProxyTest.php

@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Structural;
+
+use Tests\TestCase;
+use Twent\DesignPatterns\Structural\Proxy\BankAccountProxy;
+
+final class ProxyTest extends TestCase
+{
+    public function testProxyPatternWorksFine(): void
+    {
+        $bankAccount = new BankAccountProxy();
+        $bankAccount->deposit(3000);
+        $this->assertSame(3000, $bankAccount->getBalance());
+
+        $bankAccount->deposit(5000);
+        // Heavy operations isn't running again
+        $this->assertSame(3000, $bankAccount->getBalance());
+    }
+}