case fee total updates when a fee is updated

modules/opencase_cases/opencase_cases.module

@@ -96,36 +96,19 @@ function opencase_cases_get_activities(Drupal\opencase_cases\entity\OCCase $case
   return $activities;
 }
 
-function opencase_cases_get_amount(Drupal\opencase_cases\entity\OCCaseFee $case_fee): string {
-  if (!isEmpty($case_fee->amount)) return $case_fee->amount->first()->value;
-  else return '0';
-}
-
-function opencase_cases_get_case(Drupal\opencase_cases\entity\OCCaseFee $case_fee): Drupal\opencase_cases\entity\OCCase {
-  return $case_fee->oc_case->referencedEntities()[0];
-}
-
-function opencase_cases_update_total_fee_for_case_belonging_to_case_fee(Drupal\opencase_cases\entity\OCCaseFee $case_fee): void {
-  $total = 0;
-  $case = opencase_cases_get_case($case_fee);
-  $case_fees = opencase_cases_get_case_fees($case);
-  foreach($case_fees as $case_fee) {
-    $total += opencase_cases_get_amount($case_fee);
-  }
-  $case->set('total_fee', $total);  
-  $case->save();
-}
-
 function opencase_cases_oc_case_fee_update(Drupal\opencase_cases\entity\OCCaseFee $case_fee): void {
-  opencase_cases_update_total_fee_for_case_belonging_to_case_fee($case_fee);
+  $case = $case_fee->getCase();
+  $case->addToTotalFee($case_fee->amount->value - $case_fee->original->amount->value);
 }
 
 function opencase_cases_oc_case_fee_insert(Drupal\opencase_cases\entity\OCCaseFee $case_fee): void {
-  opencase_cases_update_total_fee_for_case_belonging_to_case_fee($case_fee);
+  $case = $case_fee->getCase();
+  $case->addToTotalFee($case_fee->amount->value);
 }
 
 function opencase_cases_oc_case_fee_delete(Drupal\opencase_cases\entity\OCCaseFee $case_fee): void {
-  opencase_cases_update_total_fee_for_case_belonging_to_case_fee($case_fee);
+  $case = $case_fee->getCase();
+  $case->addToTotalFee(0 - $case_fee->amount->value);
 }
 
 function opencase_cases_entity_base_field_info($entity_type) {

modules/opencase_cases/src/Entity/OCCase.php

@@ -222,6 +222,10 @@ class OCCase extends RevisionableContentEntityBase implements OCCaseInterface
     return $this;
   }
 
+  public function addToTotalFee(float $amountToAdd): void {
+    $this->set('total_fee', $this->total_fee->value + $amountToAdd);
+    $this->save();
+  }
 
   /**
    * {@inheritdoc}

modules/opencase_cases/src/Entity/OCCaseFee.php

@@ -190,6 +190,10 @@ class OCCaseFee extends EditorialContentEntityBase implements OCCaseFeeInterface
     return $this;
   }
 
+  public function getCase():\Drupal\opencase_cases\Entity\OCCase {
+    return \Drupal\opencase_cases\Entity\OCCase::load($this->oc_case->target_id);
+  }
+
   /**
    * {@inheritdoc}
    */