From 7c809a5bf9aabb25d11e1726d20804776c6c7c92 Mon Sep 17 00:00:00 2001
From: Mark Murray <mark.murray@shopify.com>
Date: Thu, 8 Oct 2026 12:01:51 +0100
Subject: [PATCH] Ignore duplicate Swift checkout presentations

---
 .../ShopifyCheckoutKit.swift                  | 26 +++++-
 .../ShopifyCheckoutKitTests.swift             | 80 +++++++++++++++++++
 2 files changed, 102 insertions(+), 4 deletions(-)

diff --git a/platforms/swift/Sources/ShopifyCheckoutKit/ShopifyCheckoutKit.swift b/platforms/swift/Sources/ShopifyCheckoutKit/ShopifyCheckoutKit.swift
index 3df1996f2..85baf1cff 100644
--- a/platforms/swift/Sources/ShopifyCheckoutKit/ShopifyCheckoutKit.swift
+++ b/platforms/swift/Sources/ShopifyCheckoutKit/ShopifyCheckoutKit.swift
@@ -67,18 +67,36 @@ public func invalidate() {
     CheckoutWebView.preloadCache.evict(with: .idle)
 }
 
+/// Presents checkout, or returns the existing checkout in the presenter’s modal hierarchy.
+/// Duplicate calls preserve the original checkout URL and delegate, including during dismissal.
 @MainActor
 @discardableResult
 public func present(checkout url: URL, from: UIViewController, delegate: (any CheckoutDelegate)? = nil) -> CheckoutViewController {
-    let decorated = CheckoutURLDecorator.decorate(url)
-    let viewController = CheckoutViewController(checkout: decorated, delegate: delegate)
-    from.present(viewController, animated: true)
-    return viewController
+    presentCheckout(checkout: url, from: from, delegate: delegate)
 }
 
 @MainActor
 @discardableResult
 package func present(checkout url: URL, from: UIViewController, entryPoint: MetaData.EntryPoint, delegate: (any CheckoutDelegate)? = nil, client: (any CheckoutCommunicationProtocol)? = nil) -> CheckoutViewController {
+    presentCheckout(checkout: url, from: from, delegate: delegate, client: client, entryPoint: entryPoint)
+}
+
+@MainActor
+private func presentCheckout(checkout url: URL, from: UIViewController, delegate: (any CheckoutDelegate)?, client: (any CheckoutCommunicationProtocol)? = nil, entryPoint: MetaData.EntryPoint? = nil) -> CheckoutViewController {
+    // Start at the root so calls from a checkout child or a modal above it share the same guard.
+    var root = from
+    while let ancestor = root.parent ?? root.presentingViewController {
+        root = ancestor
+    }
+    var presented: UIViewController? = root
+    while let current = presented {
+        if let checkout = current as? CheckoutViewController {
+            OSLogger.shared.warn("Checkout is already presented; ignoring duplicate presentation.")
+            return checkout
+        }
+        presented = current.presentedViewController
+    }
+
     let decorated = CheckoutURLDecorator.decorate(url)
     let viewController = CheckoutViewController(checkout: decorated, delegate: delegate, client: client, entryPoint: entryPoint)
     from.present(viewController, animated: true)
diff --git a/platforms/swift/Tests/ShopifyCheckoutKitTests/ShopifyCheckoutKitTests.swift b/platforms/swift/Tests/ShopifyCheckoutKitTests/ShopifyCheckoutKitTests.swift
index 958f0bdb2..e9691e9db 100644
--- a/platforms/swift/Tests/ShopifyCheckoutKitTests/ShopifyCheckoutKitTests.swift
+++ b/platforms/swift/Tests/ShopifyCheckoutKitTests/ShopifyCheckoutKitTests.swift
@@ -90,6 +90,70 @@ class ShopifyCheckoutKitTests: XCTestCase {
         XCTAssertNotNil(webViewController.checkoutView?.client)
     }
 
+    func test_present_duplicatePreservesCheckoutAndDelegate() throws {
+        let presenter = RecordingCheckoutPresenter()
+        let originalDelegate = MockCheckoutDelegate()
+        let checkout = ShopifyCheckoutKit.present(checkout: checkoutURL, from: presenter, delegate: originalDelegate)
+
+        let duplicate = try ShopifyCheckoutKit.present(
+            checkout: XCTUnwrap(URL(string: "https://shop.example/checkouts/cn/other")),
+            from: presenter,
+            delegate: MockCheckoutDelegate()
+        )
+
+        XCTAssertTrue(duplicate === checkout)
+        XCTAssertEqual(presenter.presentationCount, 1)
+        let content = try XCTUnwrap(checkout.viewControllers.first as? CheckoutWebViewController)
+        XCTAssertTrue(content.delegate === originalDelegate)
+    }
+
+    func test_present_fromCheckoutOrItsChildReturnsExistingCheckout() throws {
+        let presenter = RecordingCheckoutPresenter()
+        let checkout = ShopifyCheckoutKit.present(checkout: checkoutURL, from: presenter)
+        let child = try XCTUnwrap(checkout.viewControllers.first)
+
+        XCTAssertTrue(ShopifyCheckoutKit.present(checkout: checkoutURL, from: checkout) === checkout)
+        XCTAssertTrue(ShopifyCheckoutKit.present(checkout: checkoutURL, from: child) === checkout)
+        XCTAssertEqual(presenter.presentationCount, 1)
+    }
+
+    func test_present_fromContainerChildFindsPresentedCheckout() {
+        let presenter = RecordingCheckoutPresenter()
+        let child = UIViewController()
+        presenter.addChild(child)
+        let checkout = ShopifyCheckoutKit.present(checkout: checkoutURL, from: presenter)
+
+        XCTAssertTrue(ShopifyCheckoutKit.present(checkout: checkoutURL, from: child) === checkout)
+        XCTAssertEqual(presenter.presentationCount, 1)
+    }
+
+    func test_present_acceleratedEntryPointUsesSameGuard() {
+        let presenter = RecordingCheckoutPresenter()
+        let checkout = ShopifyCheckoutKit.present(checkout: checkoutURL, from: presenter, entryPoint: .acceleratedCheckouts)
+
+        XCTAssertTrue(ShopifyCheckoutKit.present(checkout: checkoutURL, from: presenter) === checkout)
+        XCTAssertTrue(ShopifyCheckoutKit.present(checkout: checkoutURL, from: presenter, entryPoint: .acceleratedCheckouts) === checkout)
+        XCTAssertEqual(presenter.presentationCount, 1)
+    }
+
+    func test_present_afterDismissalCreatesNewCheckoutEvenWhenOldControllerIsRetained() {
+        let presenter = RecordingCheckoutPresenter()
+        let checkout = ShopifyCheckoutKit.present(checkout: checkoutURL, from: presenter)
+        presenter.modal = nil
+
+        let next = ShopifyCheckoutKit.present(checkout: checkoutURL, from: presenter)
+
+        XCTAssertFalse(next === checkout)
+        XCTAssertEqual(presenter.presentationCount, 2)
+    }
+
+    func test_present_independentPresentersCanPresentTheirOwnCheckout() {
+        let first = ShopifyCheckoutKit.present(checkout: checkoutURL, from: RecordingCheckoutPresenter())
+        let second = ShopifyCheckoutKit.present(checkout: checkoutURL, from: RecordingCheckoutPresenter())
+
+        XCTAssertFalse(first === second)
+    }
+
     func test_logger_withDifferentLogLevels_shouldHaveCorrectLogLevel() {
         ShopifyCheckoutKit.configuration.logLevel = .debug
         XCTAssertEqual(
@@ -142,3 +206,19 @@ class ShopifyCheckoutKitTests: XCTestCase {
         )
     }
 }
+
+@MainActor
+private final class RecordingCheckoutPresenter: UIViewController {
+    var modal: UIViewController?
+    private(set) var presentationCount = 0
+
+    override var presentedViewController: UIViewController? {
+        modal
+    }
+
+    override func present(_ viewControllerToPresent: UIViewController, animated _: Bool, completion: (() -> Void)? = nil) {
+        presentationCount += 1
+        modal = viewControllerToPresent
+        completion?()
+    }
+}