Refactored example of Proxy pattern

Structural/Proxy/BankAccount.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace DesignPatterns\Structural\Proxy;
+
+interface BankAccount
+{
+    public function deposit(int $amount);
+
+    public function getBalance(): int;
+}

Structural/Proxy/BankAccountProxy.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace DesignPatterns\Structural\Proxy;
+
+class BankAccountProxy extends HeavyBankAccount implements BankAccount
+{
+    /**
+     * @var int
+     */
+    private $balance;
+
+    public function getBalance(): int
+    {
+        // because calculating balance is so expensive,
+        // the usage of BankAccount::getBalance() is delayed until it really is needed
+        // and will not be calculated again for this instance
+
+        if ($this->balance === null) {
+            $this->balance = parent::getBalance();
+        }
+
+        return $this->balance;
+    }
+}

Structural/Proxy/HeavyBankAccount.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace DesignPatterns\Structural\Proxy;
+
+class HeavyBankAccount implements BankAccount
+{
+    /**
+     * @var int[]
+     */
+    private $transactions = [];
+
+    public function deposit(int $amount)
+    {
+        $this->transactions[] = $amount;
+    }
+
+    public function getBalance(): int
+    {
+        // this is the heavy part, imagine all the transactions even from
+        // years and decades ago must be fetched from a database or web service
+        // and the balance must be calculated from it
+
+        return array_sum($this->transactions);
+    }
+}

Structural/Proxy/README.rst

@@ -25,15 +25,21 @@ Code
 
 You can also find this code on `GitHub`_
 
-Record.php
+BankAccount.php
 
-.. literalinclude:: Record.php
+.. literalinclude:: BankAccount.php
    :language: php
    :linenos:
 
-RecordProxy.php
+HeavyBankAccount.php
 
-.. literalinclude:: RecordProxy.php
+.. literalinclude:: HeavyBankAccount.php
+   :language: php
+   :linenos:
+
+BankAccountProxy.php
+
+.. literalinclude:: BankAccountProxy.php
    :language: php
    :linenos:
 

Structural/Proxy/Record.php

@@ -1,40 +0,0 @@
-<?php
-
-namespace DesignPatterns\Structural\Proxy;
-
-/**
- * @property string username
- */
-class Record
-{
-    /**
-     * @var string[]
-     */
-    private $data;
-
-    /**
-     * @param string[] $data
-     */
-    public function __construct(array $data = [])
-    {
-        $this->data = $data;
-    }
-
-    /**
-     * @param string $name
-     * @param string  $value
-     */
-    public function __set(string $name, string $value)
-    {
-        $this->data[$name] = $value;
-    }
-
-    public function __get(string $name): string
-    {
-        if (!isset($this->data[$name])) {
-            throw new \OutOfRangeException('Invalid name given');
-        }
-
-        return $this->data[$name];
-    }
-}

Structural/Proxy/RecordProxy.php

@@ -1,49 +0,0 @@
-<?php
-
-namespace DesignPatterns\Structural\Proxy;
-
-class RecordProxy extends Record
-{
-    /**
-     * @var bool
-     */
-    private $isDirty = false;
-
-    /**
-     * @var bool
-     */
-    private $isInitialized = false;
-
-    /**
-     * @param array $data
-     */
-    public function __construct(array $data)
-    {
-        parent::__construct($data);
-
-        // when the record has data, mark it as initialized
-        // since Record will hold our business logic, we don't want to
-        // implement this behaviour there, but instead in a new proxy class
-        // that extends the Record class
-        if (count($data) > 0) {
-            $this->isInitialized = true;
-            $this->isDirty = true;
-        }
-    }
-
-    /**
-     * @param string $name
-     * @param string  $value
-     */
-    public function __set(string $name, string $value)
-    {
-        $this->isDirty = true;
-
-        parent::__set($name, $value);
-    }
-
-    public function isDirty(): bool
-    {
-        return $this->isDirty;
-    }
-}

Structural/Proxy/Tests/ProxyTest.php

@@ -2,24 +2,23 @@
 
 namespace DesignPatterns\Structural\Proxy\Tests;
 
-use DesignPatterns\Structural\Proxy\RecordProxy;
+use DesignPatterns\Structural\Proxy\BankAccountProxy;
 use PHPUnit\Framework\TestCase;
 
 class ProxyTest extends TestCase
 {
-    public function testWillSetDirtyFlagInProxy()
+    public function testProxyWillOnlyExecuteExpensiveGetBalanceOnce()
     {
-        $recordProxy = new RecordProxy([]);
+        $bankAccount = new BankAccountProxy();
-        $recordProxy->username = 'baz';
+        $bankAccount->deposit(30);
 
-        $this->assertTrue($recordProxy->isDirty());
+        // this time balance is being calculated
-    }
+        $this->assertEquals(0, $bankAccount->getBalance());
 
-    public function testProxyIsInstanceOfRecord()
+        // inheritance allows for BankAccountProxy to behave to an outsider exactly like ServerBankAccount
-    {
+        $bankAccount->deposit(50);
-        $recordProxy = new RecordProxy([]);
-        $recordProxy->username = 'baz';
 
-        $this->assertInstanceOf(RecordProxy::class, $recordProxy);
+        // this time the previously calculated balance is returned again without re-calculating it
+        $this->assertEquals(0, $bankAccount->getBalance());
     }
 }

Structural/Proxy/uml/Proxy.uml

@@ -1,22 +1,37 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <Diagram>
   <ID>PHP</ID>
-  <OriginalElement>\DesignPatterns\Structural\Proxy\Record</OriginalElement>
+  <OriginalElement>\DesignPatterns\Structural\Proxy\BankAccount</OriginalElement>
   <nodes>
-    <node x="4.0" y="0.0">\DesignPatterns\Structural\Proxy\Record</node>
+    <node x="7.5" y="282.0">\DesignPatterns\Structural\Proxy\BankAccountProxy</node>
-    <node x="0.0" y="159.0">\DesignPatterns\Structural\Proxy\RecordProxy</node>
+    <node x="-58.0" y="123.0">\DesignPatterns\Structural\Proxy\HeavyBankAccount</node>
+    <node x="45.0" y="0.0">\DesignPatterns\Structural\Proxy\BankAccount</node>
   </nodes>
   <notes />
   <edges>
-    <edge source="\DesignPatterns\Structural\Proxy\RecordProxy" target="\DesignPatterns\Structural\Proxy\Record">
+    <edge source="\DesignPatterns\Structural\Proxy\HeavyBankAccount" target="\DesignPatterns\Structural\Proxy\BankAccount">
-      <point x="0.0" y="-54.5" />
+      <point x="0.0" y="-48.0" />
-      <point x="0.0" y="54.5" />
+      <point x="21.5" y="98.0" />
+      <point x="84.75" y="98.0" />
+      <point x="-39.75" y="36.5" />
+    </edge>
+    <edge source="\DesignPatterns\Structural\Proxy\BankAccountProxy" target="\DesignPatterns\Structural\Proxy\BankAccount">
+      <point x="37.5" y="-37.0" />
+      <point x="120.0" y="243.0" />
+      <point x="164.5" y="243.0" />
+      <point x="164.5" y="161.0" />
+      <point x="165.25" y="105.0" />
+      <point x="39.75" y="36.5" />
+    </edge>
+    <edge source="\DesignPatterns\Structural\Proxy\BankAccountProxy" target="\DesignPatterns\Structural\Proxy\HeavyBankAccount">
+      <point x="-37.5" y="-37.0" />
+      <point x="45.0" y="247.0" />
+      <point x="21.5" y="247.0" />
+      <point x="0.0" y="48.0" />
     </edge>
   </edges>
-  <settings layout="Hierarchic Group" zoom="1.0" x="81.0" y="134.0" />
+  <settings layout="Hierarchic Group" zoom="1.0" x="73.0" y="178.0" />
-  <SelectedNodes>
+  <SelectedNodes />
-    <node>\DesignPatterns\Structural\Proxy\Record</node>
-  </SelectedNodes>
   <Categories>
     <Category>Fields</Category>
     <Category>Constants</Category>