Remove net_amount from the Back office contribution form.

Net amount is calculated in the BAO if not set so asking users to enter it does not gain us anything.

Currently we require them to calculate it & edit it if they change the fee_amount or total_amount
and we validate their data entry, and make them re-do it if they get it wrong.

Since the field is pretty hidden it's unintuitive to need to change it and
makes for a painful contribution update process.

The current behaviour dates back to svn days - however since 2015 the BAO has handled the possibility
of it not being set.

In addition we have had code issues with the comparison around currency & float comparison issues
eg. #11485
and https://lab.civicrm.org/dev/core/issues/260 ( in the latter case the data saves
correctly without net_amount and incorrectly if it is changed to meet the form validation rule.
(There was a proposal in Mar 2017 to address that #9948 (comment) by fixing the calculation but I believe just dropping the field is better).

Our unit tests test the form submissions but for some reason net_amoutn was removed from the tests
https://github.com/civicrm/civicrm-core/pull/9948/files#diff-40e2e0f106ba620465acf3a9a81f2498L1535
meaning our test coverage is more reliable without it being set.

CRM/Contribute/Form/Contribution.php

@@ -378,7 +378,7 @@ public function setDefaultValues() {
       }
     }
 
-    $amountFields = array('non_deductible_amount', 'fee_amount', 'net_amount');
+    $amountFields = array('non_deductible_amount', 'fee_amount');
     foreach ($amountFields as $amt) {
       if (isset($defaults[$amt])) {
         $defaults[$amt] = CRM_Utils_Money::format($defaults[$amt], NULL, '%a');
@@ -535,7 +535,6 @@ public function buildQuickForm() {
       'invoice_id',
       'non_deductible_amount',
       'fee_amount',
-      'net_amount',
     );
     foreach ($additionalDetailFields as $key) {
       if (!empty($defaults[$key])) {
@@ -883,13 +882,6 @@ public static function formRule($fields, $files, $self) {
 
     $softErrors = CRM_Contribute_Form_SoftCredit::formRule($fields, $errors, $self);
 
-    if (!empty($fields['total_amount']) && (!empty($fields['net_amount']) || !empty($fields['fee_amount']))) {
-      $sum = CRM_Utils_Rule::cleanMoney($fields['net_amount']) + CRM_Utils_Rule::cleanMoney($fields['fee_amount']);
-      if (CRM_Utils_Rule::cleanMoney($fields['total_amount']) != $sum) {
-        $errors['total_amount'] = ts('The sum of fee amount and net amount must be equal to total amount');
-      }
-    }
-
     //CRM-16285 - Function to handle validation errors on form, for recurring contribution field.
     CRM_Contribute_BAO_ContributionRecur::validateRecurContribution($fields, $files, $self, $errors);
 

templates/CRM/Contribute/Form/AdditionalInfo/AdditionalDetail.tpl

@@ -33,8 +33,6 @@
             <span class="description">{ts}Non-deductible portion of this contribution.{/ts}</span></td></tr>
         <tr class="crm-contribution-form-block-fee_amount"><td class="label">{$form.fee_amount.label}</td><td{$valueStyle}>{$form.fee_amount.html|crmMoney:$currency:'XXX':'YYY'}<br />
             <span class="description">{ts}Processing fee for this transaction (if applicable).{/ts}</span></td></tr>
-
-        <tr class="crm-contribution-form-block-net_amount"><td class="label">{$form.net_amount.label}</td><td{$valueStyle}>{$form.net_amount.html|crmMoney:$currency:'':1}<br />
             <span class="description">{ts}Net value of the contribution (Total Amount minus Fee).{/ts}</span></td></tr>
         <tr class="crm-contribution-form-block-invoice_id"><td class="label">{$form.invoice_id.label}</td><td{$valueStyle}>{$form.invoice_id.html}<br />
             <span class="description">{ts}Unique internal reference ID for this contribution.{/ts}</span></td></tr>

templates/CRM/Contribute/Form/Contribution.tpl

@@ -44,15 +44,15 @@
     {/if}
   </div>
   {/if}
-  
+
   <div class="crm-block crm-form-block crm-contribution-form-block">
 
   {if !$email and $action neq 8 and $context neq 'standalone'}
   <div class="messages status no-popup">
     <div class="icon inform-icon"></div>&nbsp;{ts}You will not be able to send an automatic email receipt for this contribution because there is no email address recorded for this contact. If you want a receipt to be sent when this contribution is recorded, click Cancel and then click Edit from the Summary tab to add an email address before recording the contribution.{/ts}
   </div>
   {/if}
-  
+
   {if $action eq 8}
   <div class="messages status no-popup">
     <div class="icon inform-icon"></div>
@@ -590,15 +590,6 @@ function showStartDate( ) {
 var thousandMarker = "{/literal}{$config->monetaryThousandSeparator}{literal}";
 var separator = "{/literal}{$config->monetaryDecimalPoint}{literal}";
 
-cj('#fee_amount').change( function() {
-  var totalAmount = cj('#total_amount').val().replace(thousandMarker,'').replace(separator,'.');
-  var feeAmount = cj('#fee_amount').val().replace(thousandMarker,'').replace(separator,'.');
-  var netAmount = totalAmount - feeAmount;
-  if (totalAmount) {
-    cj('#net_amount').val(CRM.formatMoney(netAmount, true));
-  }
-});
-
 cj("#financial_type_id").on("change",function(){
     cj('#total_amount').trigger("change");
 })