feat: limit purchase of a network membership

includes/woocommerce-memberships/class-limit-purchase.php

@@ -20,26 +20,36 @@ class Limit_Purchase {
 	public static function init() {
 		add_filter( 'woocommerce_subscription_is_purchasable', [ __CLASS__, 'restrict_network_subscriptions' ], 10, 2 );
 		add_filter( 'woocommerce_cart_product_cannot_be_purchased_message', [ __CLASS__, 'woocommerce_cart_product_cannot_be_purchased_message' ], 10, 2 );
+
+		// Also limit purchase for logged out users, inferring their IDs from the email.
+		add_action( 'woocommerce_after_checkout_validation', [ __CLASS__, 'validate_network_subscription' ], 10, 2 );
 	}
 
 	/**
-	 * Restricts subscription purchasing from a network-synchronized plan to one.
+	 * Restricts subscription purchasing from a network-synchronized plan to one for logged in readers.
 	 *
 	 * @param bool                                                        $purchasable Whether the subscription product is purchasable.
 	 * @param \WC_Product_Subscription|\WC_Product_Subscription_Variation $subscription_product The subscription product.
 	 * @return bool
 	 */
 	public static function restrict_network_subscriptions( $purchasable, $subscription_product ) {
+		if ( ! is_user_logged_in() ) {
+			return $purchasable;
+		}
 		return self::get_network_equivalent_subscription_for_current_user( $subscription_product ) ? false : $purchasable;
 	}
 
 	/**
-	 * Given a product, check if the current user has an active subscription in another site that gives access to the same membership.
+	 * Given a product, check if the user has an active subscription in another site that gives access to the same membership.
 	 *
 	 * @param \WC_Product $product Product data.
+	 * @param int|null    $user_id User ID, defaults to the current user.
 	 */
-	private static function get_network_equivalent_subscription_for_current_user( \WC_Product $product ) {
-		$user_id = get_current_user_id();
+	private static function get_network_equivalent_subscription_for_current_user( \WC_Product $product, $user_id = null ) {
+		if ( is_null( $user_id ) ) {
+			$user_id = self::get_user_id_from_email();
+		}
+
 		if ( ! $user_id ) {
 			return;
 		}
@@ -105,4 +115,48 @@ public static function woocommerce_cart_product_cannot_be_purchased_message( $me
 		}
 		return $message;
 	}
+
+	/**
+	 * Get user from email.
+	 *
+	 * @return false|int User ID if found by email address, false otherwise.
+	 */
+	private static function get_user_id_from_email() {
+		$billing_email = filter_input( INPUT_POST, 'billing_email', FILTER_SANITIZE_EMAIL );
+		if ( $billing_email ) {
+			$customer = \get_user_by( 'email', $billing_email );
+			if ( $customer ) {
+				return $customer->ID;
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * Validate network subscription for logged out readers.
+	 *
+	 * @param array     $data   Checkout data.
+	 * @param WC_Errors $errors Checkout errors.
+	 */
+	public static function validate_network_subscription( $data, $errors ) {
+		if ( is_user_logged_in() || ! function_exists( 'WC' ) ) {
+			return;
+		}
+		$id_from_email = self::get_user_id_from_email();
+		if ( $id_from_email ) {
+			$cart_items = WC()->cart->get_cart();
+			foreach ( $cart_items as $cart_item ) {
+				$product = $cart_item['data'];
+				$network_active_subscription = self::get_network_equivalent_subscription_for_current_user( $product, $id_from_email );
+				if ( $network_active_subscription ) {
+					$error_message = sprintf(
+						/* translators: %s: Site URL */
+						__( "You can't buy this subscription because you already have it active on %s", 'newspack-network' ),
+						$network_active_subscription['site']
+					);
+					$errors->add( 'network_subscription', $error_message );
+				}
+			}
+		}
+	}
 }