Add read item user activity for handoff

Reader/FervorController.swift

@@ -155,6 +155,17 @@ actor FervorController {
         }
     }
     
+    @MainActor
+    func fetchItem(id: String) async throws -> Item? {
+        guard let serverItem = try await client.item(id: id) else {
+            return nil
+        }
+        let item = Item(context: persistentContainer.viewContext)
+        item.updateFromServer(serverItem)
+        try persistentContainer.saveViewContext()
+        return item
+    }
+    
 }
 
 extension FervorController {

Reader/Info.plist

@@ -8,6 +8,7 @@
 		<string>$(PRODUCT_BUNDLE_IDENTIFIER).activity.read-all</string>
 		<string>$(PRODUCT_BUNDLE_IDENTIFIER).activity.read-feed</string>
 		<string>$(PRODUCT_BUNDLE_IDENTIFIER).activity.read-group</string>
+		<string>$(PRODUCT_BUNDLE_IDENTIFIER).activity.read-item</string>
 		<string>$(PRODUCT_BUNDLE_IDENTIFIER).activity.preferences</string>
 		<string>$(PRODUCT_BUNDLE_IDENTIFIER).activity.add-account</string>
 		<string>$(PRODUCT_BUNDLE_IDENTIFIER).activity.activate-account</string>

Reader/SceneDelegate.swift

@@ -47,7 +47,7 @@ class SceneDelegate: UIResponder, UIWindowSceneDelegate {
                 syncFromServer()
                 createAppUI()
                 if let activity = activity {
-                    setupUI(from: activity)
+                    await setupUI(from: activity)
                 }
                 setupSceneActivationConditions()
             }
@@ -109,10 +109,12 @@ class SceneDelegate: UIResponder, UIWindowSceneDelegate {
     }
     
     func scene(_ scene: UIScene, continue userActivity: NSUserActivity) {
-        setupUI(from: userActivity)
+        Task { @MainActor in
+            await setupUI(from: userActivity)
+        }
     }
     
-    private func setupUI(from activity: NSUserActivity) {
+    private func setupUI(from activity: NSUserActivity) async {
         guard let split = window?.rootViewController as? AppSplitViewController else {
             logger.error("Failed to setup UI for user activity: missing split VC")
             return
@@ -140,7 +142,23 @@ class SceneDelegate: UIResponder, UIWindowSceneDelegate {
             if let group = try? fervorController.persistentContainer.viewContext.fetch(req).first {
                 split.showItemList(.group(group))
             }
+        case NSUserActivity.readItemType:
+            guard let itemID = activity.itemID else {
+                break
+            }
+            let req = Item.fetchRequest()
+            req.predicate = NSPredicate(format: "id = %@", itemID)
+            var read: ReadViewController? = nil
+            if let item = try? fervorController.persistentContainer.viewContext.fetch(req).first {
+                read = split.showItem(item)
+            } else {
+                if let item = try? await fervorController.fetchItem(id: itemID) {
+                    read = split.showItem(item)
+                }
+            }
+            read?.restoreUserActivityState(activity)
         default:
+            logger.warning("Unknown user activity type: \(activity.activityType)")
             break
         }
     }

Reader/Screens/AppSplitViewController.swift

@@ -66,6 +66,33 @@ class AppSplitViewController: UISplitViewController {
         home.selectItem(type)
     }
     
+    func showItem(_ item: Item) -> ReadViewController {
+        if traitCollection.horizontalSizeClass == .compact {
+            let nav = viewController(for: .compact) as! UINavigationController
+            // todo: should we try to show the right items list?
+            while nav.viewControllers.count > 2 {
+                if let current = nav.topViewController as? ReadViewController,
+                   current.item == item {
+                    return current
+                } else {
+                    nav.popViewController(animated: false)
+                }
+            }
+            let read = ReadViewController(item: item, fervorController: fervorController)
+            nav.pushViewController(read, animated: false)
+            return read
+        } else {
+            if let current = secondaryNav.topViewController as? ReadViewController,
+               current.item == item {
+                return current
+            } else {
+                let read = ReadViewController(item: item, fervorController: fervorController)
+                secondaryNav.setViewControllers([read], animated: false)
+                return read
+            }
+        }
+    }
+
 }
 
 extension AppSplitViewController: ItemsViewControllerDelegate {

Reader/Screens/Read/ReadViewController.swift

@@ -9,6 +9,7 @@ import UIKit
 import WebKit
 import HTMLEntities
 import SafariServices
+import Combine
 
 class ReadViewController: UIViewController {
     
@@ -22,6 +23,10 @@ class ReadViewController: UIViewController {
     let fervorController: FervorController
     let item: Item
     
+    private let scrollPositionChangedSubject = PassthroughSubject<Void, Never>()
+    private var cancellables = Set<AnyCancellable>()
+    private var scrollTargetSelector: String?
+    
     private var webView: WKWebView!
     
     #if targetEnvironment(macCatalyst)
@@ -41,6 +46,8 @@ class ReadViewController: UIViewController {
         self.item = item
         
         super.init(nibName: nil, bundle: nil)
+        
+        self.userActivity = .readItem(item, account: fervorController.account!)
     }
     
     required init?(coder: NSCoder) {
@@ -59,6 +66,7 @@ class ReadViewController: UIViewController {
         webView.translatesAutoresizingMaskIntoConstraints = false
         webView.navigationDelegate = self
         webView.uiDelegate = self
+        webView.scrollView.delegate = self
         // transparent background required to prevent white flash in dark mode, just using .appBackground doesn't work
         webView.isOpaque = false
         webView.backgroundColor = .clear
@@ -78,6 +86,13 @@ class ReadViewController: UIViewController {
             activityItemsConfiguration = UIActivityItemsConfiguration(objects: [url as NSURL])
         }
         
+        scrollPositionChangedSubject
+            .debounce(for: .milliseconds(500), scheduler: RunLoop.main)
+            .sink { [unowned self] in
+                self.updateUserActivityScrollPosition()
+            }
+            .store(in: &cancellables)
+        
         #if targetEnvironment(macCatalyst)
         itemReadObservation = item.observe(\.read) { [unowned self] _, _ in
             self.updateToggleReadToolbarImage()
@@ -97,6 +112,44 @@ class ReadViewController: UIViewController {
         updateScrollIndicatorStyle()
     }
     
+    override func restoreUserActivityState(_ activity: NSUserActivity) {
+        if let selector = activity.topElementSelector {
+            scrollTargetSelector = selector
+            if isViewLoaded {
+                scrollToTargetSelector()
+            }
+        }
+    }
+    
+    private func scrollToTargetSelector() {
+        guard let selector = scrollTargetSelector else {
+            return
+        }
+        
+        let js = """
+        const doScroll = () => {
+            const el = document.querySelector(sel);
+            if (!el) {
+                throw new Error("not ready yet");
+            }
+            el.scrollIntoView();
+        };
+        if (document.readyState !== "complete") {
+            window.addEventListener("load", doScroll);
+        } else {
+            doScroll();
+        }
+        """
+        webView.callAsyncJavaScript(js, arguments: ["sel": selector], in: nil, in: .defaultClient) { result in
+            switch result {
+            case .failure(let error):
+                print(error)
+            case .success(_):
+                self.scrollTargetSelector = nil
+            }
+        }
+    }
+    
     private func updateScrollIndicatorStyle() {
         guard #available(iOS 15.4, *) else {
             // different workaround pre-iOS 15.4
@@ -171,6 +224,55 @@ class ReadViewController: UIViewController {
         return vc
     }
     
+    func updateUserActivityScrollPosition() {
+        // can't use needsSave and updateUserActivityState(_:) because running JS is asynchronous
+        let js = """
+        (() => {
+            function topVisibleChild(element) {
+                if (element.children.length <= 0 || element.tagName === "svg") {
+                    return element;
+                }
+                let min, minDistanceToTop;
+                for (const c of element.children) {
+                    const rect = c.getBoundingClientRect();
+                    if (!min || Math.abs(rect.top) < minDistanceToTop) {
+                        min = c;
+                        minDistanceToTop = Math.abs(rect.top);
+                    }
+                }
+                return topVisibleChild(min);
+            }
+            function uniqueSelector(self) {
+                if (!self) {
+                    return null;
+                } else if (self.tagName === "BODY") {
+                    return "body";
+                } else {
+                    let selfSel;
+                    if (self.id) {
+                        return `#${self.id}`;
+                    } else if (Array.from(self.parentNode.children).filter((e) => e.tagName === self.tagName).length === 1) {
+                        selfSel = ` > ${self.tagName.toLowerCase()}`;
+                    } else {
+                        const index = Array.from(self.parentNode.children).indexOf(self);
+                        selfSel = ` > ${self.tagName.toLowerCase()}:nth-child(${index + 1})`;
+                    }
+                    const parentSel = uniqueSelector(self.parentNode);
+                    return parentSel + selfSel;
+                }
+            }
+            return uniqueSelector(topVisibleChild(document.getElementById("item-content")));
+        })()
+        """
+        // todo: check if <source> can be scrolled into view
+        webView.evaluateJavaScript(js) { result, error in
+            guard let result = result as? String else {
+                return
+            }
+            self.userActivity?.topElementSelector = result
+        }
+    }
+    
     #if targetEnvironment(macCatalyst)
     @objc func toggleItemRead(_ item: NSToolbarItem) {
         Task {
@@ -208,6 +310,11 @@ extension ReadViewController: WKNavigationDelegate {
             return .allow
         }
     }
+    
+    func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
+        // we try to scroll after the navigation triggered by the loadHTML, since that's asynchronous but doesn't have a callback
+        scrollToTargetSelector()
+    }
 }
 
 extension ReadViewController: WKUIDelegate {
@@ -242,6 +349,15 @@ extension ReadViewController: WKUIDelegate {
     }
 }
 
+extension ReadViewController: UIScrollViewDelegate {
+    func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
+        scrollPositionChangedSubject.send()
+    }
+    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
+        scrollPositionChangedSubject.send()
+    }
+}
+
 extension ReadViewController: StretchyMenuInteractionDelegate {
     func stretchyMenuTitle() -> String? {
         return nil

Reader/UserActivities.swift

@@ -16,6 +16,7 @@ extension NSUserActivity {
     static let readAllType = "net.shadowfacts.Reader.activity.read-all"
     static let readFeedType = "net.shadowfacts.Reader.activity.read-feed"
     static let readGroupType = "net.shadowfacts.Reader.activity.read-group"
+    static let readItemType = "net.shadowfacts.Reader.activity.read-item"
     
     func accountID() -> Data? {
         let types = [
@@ -47,6 +48,27 @@ extension NSUserActivity {
         }
     }
     
+    var itemID: String? {
+        if activityType == NSUserActivity.readItemType {
+            return userInfo?["itemID"] as? String
+        } else {
+            return nil
+        }
+    }
+    
+    var topElementSelector: String? {
+        get {
+            userInfo?["topElementSelector"] as? String
+        }
+        set {
+            if let newValue = newValue {
+                addUserInfoEntries(from: ["topElementSelector": newValue])
+            } else {
+                userInfo?.removeValue(forKey: "topElementSelector")
+            }
+        }
+    }
+
     static func preferences() -> NSUserActivity {
         return NSUserActivity(activityType: preferencesType)
     }
@@ -113,4 +135,14 @@ extension NSUserActivity {
         return activity
     }
     
+    static func readItem(_ item: Item, account: LocalData.Account) -> NSUserActivity {
+        let activity = NSUserActivity(activityType: readItemType)
+        activity.isEligibleForHandoff = true
+        activity.userInfo = [
+            "accountID": account.id,
+            "itemID": item.id!,
+        ]
+        return activity
+    }
+    
 }