Refactor invoice handling and add total net amount calculation

Introduce logic for validating booked and draft invoices in E-conomic. Add methods to calculate the total net amount for invoice collections and improve error handling for specific invoice states. Updated related workflows to ensure consistent validation and data integrity.

services/nginx/app/objects/orders_o.php

@@ -446,4 +446,22 @@ class orders_o extends db
         $result = $db->query($sql);
         return $db->fetch_all($result);
     }
+
+    public function getNetAmount(): float
+    {
+        self::requireSelected();
+        $net = 0;
+        // Get the order items object
+        $order_items = new order_items_o();
+        // Get the price, quantity of the order items
+        $items = $order_items->getAllItemsAsArray($this->id);
+        // Loop through the items and get the net amount
+        foreach ( $items as $item ) {
+            $tmp_price = (int)$item['price'];
+            $tmp_quantity = (int)$item['quantity'];
+            // Add the price to the net amount
+            $net += $tmp_price * $tmp_quantity;
+        }
+        return $net;
+    }
 }