feat: add defaultCallback method

Author: binaryk

src/Fields/Field.php

@@ -115,6 +115,8 @@ class Field extends OrganicField implements JsonSerializable
      */
     protected $valueCallback;
 
+    protected $fillDefaultCallback;
+
     /**
      * Closure be used to be called after the field value stored.
      */
@@ -205,6 +207,13 @@ public function fillCallback(callable|Closure $callback)
         return $this;
     }
 
+    public function defaultCallback(mixed $callback)
+    {
+        $this->defaultCallback = $callback;
+
+        return $this;
+    }
+
     /**
      * Fill attribute with value from the request or delegate this action to the user defined callback.
      *
@@ -246,6 +255,12 @@ public function fillAttribute(RestifyRequest $request, $model, ?int $bulkRow = n
             $bulkRow
         );
 
+        $this->fillAttributeFromDefault(
+            $request,
+            $model,
+            $this->label ?? $this->attribute
+        );
+
         $this->fillAttributeFromValue(
             $request,
             $model,
@@ -310,6 +325,23 @@ protected function fillAttributeFromValue(RestifyRequest $request, $model, $attr
         return $this;
     }
 
+    protected function fillAttributeFromDefault(RestifyRequest $request, $model, $attribute)
+    {
+        if ($model->{$attribute}) {
+            return $this;
+        }
+
+        if (! isset($this->fillDefaultCallback)) {
+            return $this;
+        }
+
+        $model->{$attribute} = is_callable($this->fillDefaultCallback)
+            ? call_user_func($this->fillDefaultCallback, $request, $model, $attribute)
+            : $this->fillDefaultCallback;
+
+        return $this;
+    }
+
     /**
      * @return callable|string|null
      */
@@ -547,7 +579,7 @@ public function label($label)
     public function serializeToValue($request)
     {
         return [
-            $this->label ?? $this->attribute => $this->value ?? $this->resolveDefaultValue($request),
+                $this->label ?? $this->attribute => $this->value ?? $this->resolveDefaultValue($request),
         ];
     }
 
@@ -563,6 +595,7 @@ public function default($callback)
         return $this;
     }
 
+
     /**
      * Resolve the default value for the field.
      *