Add NodeFilter::filter() method (#1)

* Add NodeFilter::filter() method

* Test NodeFilter::filter()

* phpstan

phpstan-baseline.neon

@@ -7,6 +7,6 @@ parameters:
 
 		-
 			message: "#^Right side of && is always true\\.$#"
-			count: 2
+			count: 3
 			path: src/NodeFilter/NodeCollection.php
 

src/NodeFilter/NodeCollection.php

@@ -69,6 +69,19 @@ public function exists(?string $selector = null): bool
         return $this->querySelector($selector)->exists();
     }
 
+    public function filter(Closure $closure): NodeFilter
+    {
+        $newDoc = new DOMDocument();
+
+        foreach ($this->nodes as $node) {
+            if ($closure(new NodeCollection($node)) && ($newNode = $newDoc->importNode($node, true))) {
+                $newDoc->appendChild($newNode);
+            }
+        }
+
+        return new NodeCollection($newDoc->childNodes);
+    }
+
     public function first(?string $selector = null): NodeFilter
     {
         if (\is_null($selector)) {

src/NodeFilter/NodeFilter.php

@@ -40,6 +40,15 @@ public function each($selector = null, ?Closure $closure = null, ?int $max = nul
      */
     public function exists(?string $selector = null): bool;
 
+    /**
+     * Filter a list of nodes using a closure that returns a boolean.
+     * The closure gets passed a node filter to test upon.
+     *
+     * @param Closure $closure
+     * @return NodeFilter
+     */
+    public function filter(Closure $closure): NodeFilter;
+
     /**
      * Create a new collection of nodes only containing the first node of the current collection.
      *

src/NodeFilter/NullNode.php

@@ -33,6 +33,11 @@ public function exists(?string $selector = null): bool
         return false;
     }
 
+    public function filter(Closure $closure): NodeFilter
+    {
+        return $this;
+    }
+
     public function first(?string $selector = null): NodeFilter
     {
         return $this;

tests/NodeFilter/NodeFilterChainTest.php

@@ -6,6 +6,7 @@
 use DOMNodeList;
 use Generator;
 use Jerodev\Diggy\NodeFilter\NodeCollection;
+use Jerodev\Diggy\NodeFilter\NodeFilter;
 use PHPUnit\Framework\TestCase;
 
 final class NodeFilterChainTest extends TestCase
@@ -95,6 +96,15 @@ public function functionProvider(): Generator
                 ['is', ['p']],
             ]
         ];
+
+        yield [
+            'two',
+            [
+                ['querySelector', ['ul li']],
+                ['filter', [static fn (NodeFilter $node) => $node->text() === 'two']],
+                ['text']
+            ]
+        ];
     }
 
     private function createDOMNodes(): DOMNodeList