Ensure no recalculations once locked

app/DataMapper/Tax/BaseRule.php

@@ -130,9 +130,8 @@ class BaseRule implements RuleInterface
         return $this;
     }
 
-    public function shouldCalcTax(): bool
+    public function shouldCalcTax(): bool {
-    {
+        return $this->should_calc_tax && $this->checkIfInvoiceLocked();
-        return $this->should_calc_tax;
     }
     /**
      * Initializes the tax rule for the entity.
@@ -400,4 +399,36 @@ class BaseRule implements RuleInterface
         return ! in_array($iso_3166_2, array_merge($this->eu_country_codes, array_keys($this->region_codes)));
     }
 
+    private function checkIfInvoiceLocked(): bool
+    {
+        $lock_invoices = $this->client->getSetting('lock_invoices');
+
+        switch ($lock_invoices) {
+            case 'off':
+                return true;
+            case 'when_sent':
+                if ($this->invoice->status_id == Invoice::STATUS_SENT) {
+                    return false;
+                }
+
+                return true;
+
+            case 'when_paid':
+                if ($this->invoice->status_id == Invoice::STATUS_PAID) {
+                    return false;
+                }
+
+                return true;
+
+                //if now is greater than the end of month the invoice was dated - do not modify
+            case 'end_of_month':
+                if(\Carbon\Carbon::parse($this->invoice->date)->setTimezone($this->invoice->company->timezone()->name)->endOfMonth()->lte(now())) {
+                    return false;
+                }
+                return true;
+            default:
+                return true;
+        }
+    }
+
 }