feat: Add ValueObject contract and implementations.

Author: b00gizm

composer.json

@@ -16,7 +16,8 @@
     ],
     "require": {
         "psr/event-dispatcher": "^1.0",
-        "beberlei/assert": "^3.3"
+        "beberlei/assert": "^3.3",
+        "ramsey/uuid": "^4.7"
     },
     "require-dev": {
         "phpunit/phpunit": "^9.5",

composer.lock

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GeekCell\Ddd\Contracts\Domain;
+
+interface ValueObject
+{
+    /**
+     * Check if the given object is equal to the current object.
+     *
+     * @param ValueObject $object
+     * @return bool
+     */
+    public function equals(ValueObject $object): bool;
+
+    /**
+     * Return the value of the value object.
+     *
+     * @return mixed
+     */
+    public function getValue(): mixed;
+
+    /**
+     * Return the string representation of the value object.
+     *
+     * @return string
+     */
+    public function __toString(): string;
+}

src/Contracts/Domain/ValueObject.php

@@ -0,0 +1,60 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GeekCell\Ddd\Domain;
+
+use GeekCell\Ddd\Contracts\Domain\ValueObject as ValueObjectInterface;
+
+abstract class ValueObject implements ValueObjectInterface
+{
+    /**
+     * ValueObject constructor.
+     *
+     * @param mixed $args
+     *
+     * @throws \Throwable
+     */
+    public function __construct(...$args)
+    {
+        $this->validate(...$args);
+    }
+
+    /**
+     * Validate the given arguments.
+     *
+     * @param mixed $args
+     * @return void
+     *
+     * @throws \Throwable
+     */
+    protected function validate(...$args): void
+    {
+        if (!$this->doValidate(...$args)) {
+            $this->raiseValidationException(...$args);
+        }
+    }
+
+    /**
+     * Raise an exception if the provided arguments to the constructor
+     * are invalid. This method can/should be overridden in the child class
+     * to raise a custom exception.
+     *
+     * @param mixed $args
+     * @return void
+     *
+     * @throws \Throwable
+     */
+    protected function raiseValidationException(...$args): void
+    {
+        throw new \InvalidArgumentException('Invalid argument(s) provided.');
+    }
+
+    /**
+     * Provides the actual validation logic.
+     *
+     * @param mixed $args
+     * @return bool
+     */
+    abstract protected function doValidate(...$args): bool;
+}