Added ModifierStack class

src/ModifierStack.php

@@ -0,0 +1,28 @@
+<?php
+
+namespace Intervention\Image;
+
+use Intervention\Image\Interfaces\ImageInterface;
+use Intervention\Image\Interfaces\ModifierInterface;
+
+class ModifierStack implements ModifierInterface
+{
+    public function __construct(protected array $modifiers)
+    {
+        //
+    }
+
+    public function apply(ImageInterface $image): ImageInterface
+    {
+        foreach ($this->modifiers as $modifier) {
+            $modifier->apply($image);
+        }
+    }
+
+    public function push(ModifierInterface $modifier): self
+    {
+        $this->modifiers[] = $modifier;
+
+        return $this;
+    }
+}

tests/ModiferStackTest.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace Intervention\Image\Tests;
+
+use Intervention\Image\Drivers\Gd\Modifiers\GreyscaleModifier;
+use Intervention\Image\ModifierStack;
+
+/**
+ * @covers \Intervention\Image\ModifierStack
+ */
+class ModifierStackTest extends TestCase
+{
+    public function testConstructor(): void
+    {
+        $stack = new ModifierStack([]);
+        $this->assertInstanceOf(ModifierStack::class, $stack);
+    }
+
+    public function testPush(): void
+    {
+        $stack = new ModifierStack([]);
+        $result = $stack->push(new GreyscaleModifier());
+        $this->assertInstanceOf(ModifierStack::class, $result);
+    }
+}