start to add ability to merge tunes

started refactoring tune builders to use string type hint instead of StringAtom

src/Domain/Core/MultivalueAttribute.php

@@ -0,0 +1,80 @@
+<?php
+
+namespace XaiCorp\AbcParser\Domain\Core;
+
+class MultivalueAttribute
+{
+    /**
+     * @var \XaiCorp\AbcParser\Domain\Core\Collection
+     */
+    protected $data;
+
+    private function __construct()
+    {
+        $this->data = new Collection();
+    }
+
+    /**
+     * @param string $item
+     * @return \XaiCorp\AbcParser\Domain\Core\MultivalueAttribute
+     */
+    public static function create(string $item)
+    {
+        return (new self())->add($item);
+    }
+
+    /**
+     * @param array $items
+     * @return \XaiCorp\AbcParser\Domain\Core\MultivalueAttribute
+     */
+    public static function createFromArray(array $items)
+    {
+        $attribute = new self();
+
+        foreach ($items as $item) {
+            $attribute->add($item);
+        }
+
+        return $attribute;
+    }
+
+    /**
+     * @param string $item
+     * @return static
+     */
+    public function add(string $item)
+    {
+        $this->data = $this->data->push($item)->unique();
+
+        return $this;
+    }
+
+    /**
+     * @param MultivalueAttribute $attribute
+     * @return static
+     */
+    public function merge(MultivalueAttribute $attribute)
+    {
+        $this->data = $this->data
+            ->pushArray($attribute->data->toArray())
+            ->unique();
+
+        return $this;
+    }
+
+    /**
+     * @return string
+     */
+    public function first()
+    {
+        return $this->data->firstOrDefault('');
+    }
+
+    /**
+     * @return string[]
+     */
+    public function toArray()
+    {
+        return $this->data->toArray();
+    }
+}