add nova

nova/src/Fields/HasPreview.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Laravel\Nova\Fields;
+
+trait HasPreview
+{
+    /**
+     * The callback used to retrieve the preview URL.
+     *
+     * @var (callable(mixed, ?string, mixed):(?string))|null
+     */
+    public $previewUrlCallback;
+
+    /**
+     * Specify the callback that should be used to retrieve the preview URL.
+     *
+     * @param  callable(mixed, ?string, mixed):?string  $previewUrlCallback
+     * @return $this
+     */
+    public function preview(callable $previewUrlCallback)
+    {
+        $this->previewUrlCallback = $previewUrlCallback;
+
+        return $this;
+    }
+
+    /**
+     * Resolve the preview URL for the field.
+     *
+     * @return string|null
+     */
+    public function resolvePreviewUrl()
+    {
+        return is_callable($this->previewUrlCallback)
+                    ? call_user_func($this->previewUrlCallback, $this->value, $this->getStorageDisk(), $this->resource)
+                    : null;
+    }
+}