Add the depth() method.

Author: drupol

spec/drupol/phptree/Node/NodeSpec.php

@@ -202,4 +202,32 @@ public function it_can_use_withChildren()
             ->children()
             ->shouldReturn([]);
     }
+
+    public function it_can_get_its_depth()
+    {
+        $this
+            ->depth()
+            ->shouldReturn(0);
+
+        $tree = new \drupol\phptree\Node\ValueNode('root', 2);
+
+        $tree->add($this->getWrappedObject());
+
+        $this
+            ->depth()
+            ->shouldReturn(1);
+
+        $nodes = [];
+        foreach (\range('A', 'Z') as $v) {
+            $nodes[] = new \drupol\phptree\Node\ValueNode($v);
+        }
+
+        $tree->add(...$nodes);
+
+        $tree->add($this->getWrappedObject());
+
+        $this
+            ->depth()
+            ->shouldReturn(4);
+    }
 }

src/Node/Node.php

@@ -174,4 +174,12 @@ public function withChildren(NodeInterface ...$nodes): NodeInterface
 
         return $clone;
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function depth(): int
+    {
+        return \count($this->getAncestors());
+    }
 }

src/Node/NodeInterface.php

@@ -97,4 +97,12 @@ public function getSibblings(): array;
      *   The amound of children.
      */
     public function degree(): int;
+
+    /**
+     * Get the node depth from the root node.
+     *
+     * @return int
+     *   The depth is the number of nodes before root.
+     */
+    public function depth(): int;
 }