Add logic for downgrades

Author: annemirasol

includes/class-wc-subscriptions-coupon.php

@@ -219,10 +219,14 @@ public static function get_discount_amount_for_cart_item( $cart_item, $discount,
 				}
 			}
 
-			// Compute the sign-up fee. If it's a switch, we need to get the signup fee less
-			// recurring payment upgrade/downgrade costs.
+			// Compute the true sign-up fee. If it's a subscription upgrade, we need to get the fee
+			// before extra charges, e.g. prorated recurring payment, were applied.
 			if ( $is_switch ) {
-				$sign_up_fee = (int) $cart_item['data']->get_meta( '_subscription_sign_up_fee_prorated' );
+				$is_downgrade = isset( $cart_item['subscription_switch']['upgraded_or_downgraded'] ) &&
+										'downgraded' === $cart_item['subscription_switch']['upgraded_or_downgraded'];
+				$sign_up_fee  = $is_downgrade ?
+										WC_Subscriptions_Product::get_sign_up_fee( $cart_item['data'] ) :
+										(int) $cart_item['data']->get_meta( '_subscription_sign_up_fee_prorated' );
 			} else {
 				$sign_up_fee = WC_Subscriptions_Product::get_sign_up_fee( $cart_item['data'] );
 			}

tests/unit/test-class-wc-subscriptions-coupon.php

@@ -100,7 +100,8 @@ public function test_get_discount_amount_for_cart_item_sign_up_fee_coupons() {
 			'data'                => $this->variable_subscription_product,
 			'quantity'            => 1,
 			'subscription_switch' => [
-				'subscription_id' => 123,
+				'subscription_id'        => 123,
+				'upgraded_or_downgraded' => 'upgraded',
 			],
 		);
 		$this->cart->empty_cart();
@@ -174,6 +175,22 @@ public function test_get_discount_amount_for_cart_item_sign_up_fee_coupons() {
 				$coupon_sign_up_fee_large
 			)
 		);
+
+		// Subscription switch -- downgrade
+		$cart_item['data']->update_meta_data( '_subscription_sign_up_fee', 10 );
+		$cart_item['data']->update_meta_data( '_subscription_sign_up_fee_prorated', 0 );
+		$cart_item['data']->update_meta_data( '_subscription_price_prorated', 0 );
+		$cart_item['subscription_switch']['upgraded_or_downgraded'] = 'downgraded';
+		$this->assertEquals(
+			1,
+			WC_Subscriptions_Coupon::get_discount_amount_for_cart_item(
+				$cart_item,
+				$discount,
+				$discounting_amount,
+				$single,
+				$coupon_sign_up_fee_percent
+			)
+		);
 	}
 
 
@@ -248,7 +265,8 @@ public function test_get_discount_amount_for_cart_item_recurring_fee_coupons() {
 			'data'                => $this->variable_subscription_product,
 			'quantity'            => 1,
 			'subscription_switch' => [
-				'subscription_id' => 123,
+				'subscription_id'        => 123,
+				'upgraded_or_downgraded' => 'upgraded',
 			],
 		);
 		$this->cart->empty_cart();