Add InvoiceService and initial invoice dashboard widget

app/Http/Controllers/InvoiceController.php

@@ -185,6 +185,19 @@ public function salesStatistics()
         return ApiDataTransformer::snakeToCamel($statistics);
     }
 
+    public static function getDueInvoices()
+    {
+        $today = date('Y-m-d');
+        $invoices = Invoice::where('due_date', '<=', $today)
+            ->whereIn('payment_status', ['issued', 'due', 'reminded'])
+            ->orderBy('due_date', 'asc')
+            ->get();
+
+        return $invoices->map(function ($invoice) {
+            return ApiDataTransformer::snakeToCamel($invoice->toArray());
+        });
+    }
+
 
     public function preview($id)
     {