CRM-19585, added function to Calculate Tax when Financial Type is cha…

…nged.

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* CRM-19585: Sales tax issue
  https://issues.civicrm.org/jira/browse/CRM-19585

CRM/Contribute/BAO/Contribution.php

@@ -5570,6 +5570,33 @@ public static function calculateTaxAfterChangeInFinancialTypeForLineItems($lineI
       }
     }
     return $taxAmount;
+
+  /**
+   * Calculate Tax when Financial Type is changed.
+   *
+   * @param array $params
+   * @param float $totalAmount
+   * @param array $oldTaxAmounts
+   * @param float $changeFTAmount
+   *
+   */
+  public static function calculateTaxForChangeInFinancialType(
+    &$params, &$totalAmount,
+    &$oldTaxAmounts, &$changeFTAmount
+  ) {
+    $taxAmountAfterFTChange = self::calculateTaxAfterChangeInFinancialTypeForLineItems($params['line_item'], $params['contribution']->id);
+    $previousTaxAmount = 0;
+    if (isset($params['prevContribution']->tax_amount)) {
+      $previousTaxAmount = $params['prevContribution']->tax_amount;
+    }
+    $taxDiff = $taxAmountAfterFTChange - $previousTaxAmount;
+    $changeFTAmount += $taxDiff;
+    $totalAmount -= $taxDiff;
+    if ($taxDiff > 0) {
+      $params['tax_amount'] = $taxAmountAfterFTChange;
+      $oldTaxAmounts['new_tax_amount'] -= $taxDiff;
+      $oldTaxAmounts['previous_tax_amount'] = $taxAmountAfterFTChange - $taxDiff;
+    }
   }
 
 }