[4.x] Allow payment currency rate override

src/events/PaymentCurrencyRateEvent.php

@@ -0,0 +1,27 @@
+<?php
+/**
+ * @link https://craftcms.com/
+ * @copyright Copyright (c) Pixel & Tonic, Inc.
+ * @license https://craftcms.github.io/license/
+ */
+
+namespace craft\commerce\events;
+
+use craft\commerce\models\Transaction;
+use yii\base\Event;
+
+/**
+ * Payment Currency Rate Event
+ *
+ * @property ?Transaction $transaction
+ * @since 2.0
+ */
+class PaymentCurrencyRateEvent extends Event
+{
+	/**
+	* @var float The rate the event
+	*/
+	public float $rate;
+
+	public ?Transaction $transaction = null;
+}

src/models/PaymentCurrency.php

@@ -8,6 +8,7 @@
 namespace craft\commerce\models;
 
 use craft\commerce\base\Model;
+use craft\commerce\events\PaymentCurrencyRateEvent;
 use craft\commerce\records\PaymentCurrency as PaymentCurrencyRecord;
 use craft\helpers\UrlHelper;
 use craft\validators\UniqueValidator;
@@ -28,7 +29,13 @@
  */
 class PaymentCurrency extends Model
 {
-    /**
+
+	/**
+	 * @event PaymentCurrencyRateEvent The event that is triggered when the payment currency rate is defined
+	 */
+	const EVENT_DEFINE_PAYMENT_CURRENCY_RATE = 'definePaymentCurrencyRate';
+
+	/**
      * @var int|null ID
      */
     public ?int $id = null;
@@ -150,6 +157,22 @@ public function setCurrency(Currency $currency): void
         $this->_currency = $currency;
     }
 
+	/**
+	 * @param Transaction|null $transaction
+	 * @return float
+	 */
+	public function getRate(Transaction $transaction = null) : float
+	{
+		$event = new PaymentCurrencyRateEvent([
+			'rate' => $this->rate,
+			'transaction' => $transaction,
+		]);
+
+		$this->trigger(self::EVENT_DEFINE_PAYMENT_CURRENCY_RATE, $event);
+
+		return $this->rate;
+	}
+
     /**
      * @inheritdoc
      */

src/services/PaymentCurrencies.php

@@ -197,10 +197,10 @@ public function convertCurrency(float $amount, string $fromCurrency, string $toC
 
         if ($this->getPrimaryPaymentCurrency()->iso != $fromCurrency) {
             // now the amount is in the primary currency
-            $amount /= $fromCurrency->rate;
+            $amount /= $fromCurrency->getRate();
         }
 
-        $result = $amount * $toCurrency->rate;
+        $result = $amount * $toCurrency->getRate();
 
         if ($round) {
             return CurrencyHelper::round($result, $toCurrency);
@@ -239,7 +239,7 @@ public function savePaymentCurrency(PaymentCurrency $model, bool $runValidation
         $record->iso = strtoupper($model->iso);
         $record->primary = $model->primary;
         // If this rate is primary, the rate must be 1 since it is now the rate all prices are enter in as.
-        $record->rate = $model->primary ? 1 : $model->rate;
+        $record->rate = $model->primary ? 1 : $model->getRate();
 
         $record->save(false);
 

src/services/Transactions.php

@@ -216,7 +216,7 @@ public function createTransaction(Order $order = null, Transaction $parentTransa
             $transaction->amount = Currency::round($amount, $currency);
 
             // Capture historical rate
-            $transaction->paymentRate = $paymentCurrency->rate;
+            $transaction->paymentRate = $paymentCurrency->getRate($transaction);
 
             $transaction->setOrder($order);
         }