Type casting causing 1 pence difference

Replicate:

1. Create a contribution page with an amount 161.70
2. Submit the form and create a mandate

Expected results

• Contribution recur amount in Civi = 161.70
• Subscription amount in GC = 161.70

Actual result:

• Contribution recur amount in Civi = 161.70
• Subscription amount in GC = 161.69

The reason for failure is because of type casting

Ref: https://stackoverflow.com/a/13104146/4286907

eg:

pradeep@Pradpnayak Documents % php -r '$a=161.70; $b = (100.00 * $a); var_dump($b);'
float(16169.999999999998)

Solution:

diff --git a/CRM/GoCardlessUtils.php b/CRM/GoCardlessUtils.php
index 3cfbdca..7b04338 100644
--- a/CRM/GoCardlessUtils.php
+++ b/CRM/GoCardlessUtils.php
@@ -134,6 +134,20 @@ class CRM_GoCardlessUtils {
     return $redirect_flow;
   }
 
+  /**
+   * Get the amount for the GC API formatted in lowest (ie. cents / pennies).
+   *
+   * @param float $amount
+   *
+   * @return int
+   */
+  public static function getAmount($amount): int {
+    $amount = number_format((float) $amount ?? 0.0, CRM_Utils_Money::getCurrencyPrecision(), '.', '');
+    // Stripe amount required in cents.
+    $amount = preg_replace('/[^\d]/', '', strval($amount));
+    return (int) $amount;
+  }
+
   /**
    * Complete a GoCardless redirect flow, set up subscription from details given.
    *
@@ -213,7 +227,7 @@ class CRM_GoCardlessUtils {
     $metadata = json_encode(array_intersect_key($deets, array_flip(['contactID', 'contributionRecurID'])));
     $params = [
     // Convert amount to pennies.
-      'amount'        => (int) (100 * $deets['amount']),
+      'amount'        => self::getAmount($deets['amount']),
       'currency'      => 'GBP',
       'name'          => $deets['description'],
       'interval'      => $interval,