Create RelationshipIterator support class

Author: huntie

src/Serializers/RelationshipSerializer.php

@@ -2,8 +2,7 @@
 
 namespace Huntie\JsonApi\Serializers;
 
-use Exception;
-use Huntie\JsonApi\Exceptions\InvalidRelationPathException;
+use Huntie\JsonApi\Support\RelationshipIterator;
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Support\Collection;
 
@@ -36,16 +35,7 @@ public function __construct($record, $path, array $fields = [])
     {
         parent::__construct();
 
-        try {
-            $this->relation = $record;
-
-            foreach (explode('.', $path) as $relation) {
-                $this->relation = $this->relation->{$relation};
-            }
-        } catch (Exception $e) {
-            throw new InvalidRelationPathException($path);
-        }
-
+        $this->relation = (new RelationshipIterator($record, $path))->resolve();
         $this->fields = array_unique($fields);
     }
 

src/Support/RelationshipIterator.php

@@ -0,0 +1,55 @@
+<?php
+
+namespace Huntie\JsonApi\Support;
+
+use InvalidArgumentException;
+use Huntie\JsonApi\Exceptions\InvalidRelationPathException;
+
+class RelationshipIterator
+{
+    /**
+     * The primary record.
+     */
+    private $record;
+
+    /**
+     * The path to the relation.
+     *
+     * @var string
+     */
+    private $path;
+
+    /**
+     * Create a new RelationshipIterator instance.
+     *
+     * @param Model  $record The primary record
+     * @param string $path   The path to the relation
+     */
+    public function __construct($record, $path)
+    {
+        if (!preg_match('/[A-Za-z.]+/', $path)) {
+            throw new InvalidArgumentException('The relationship path must be a valid string');
+        }
+
+        $this->record = $record;
+        $this->path = $path;
+    }
+
+    /**
+     * Resolve the relationship from the primary record.
+     *
+     * @throws InvalidRelationPathException
+     *
+     * @return Collection|Model|null
+     */
+    public function resolve()
+    {
+        return array_reduce(explode('.', $this->path), function ($resolved, $relation) {
+            if (is_null($resolved) || in_array($relation, $this->record->getHidden())) {
+                throw new InvalidRelationPathException($this->path);
+            }
+
+            return $resolved->{$relation};
+        }, $this->record);
+    }
+}