Don’t reload Reader views from deep links if they’re already displayed

Author: jkmassel

WordPress/Classes/System/Root View/ReaderPresenter.swift

@@ -199,6 +199,9 @@ public final class ReaderPresenter: NSObject, SplitViewDisplayable {
     /// column (split view) or pushing to the navigation stack.
     private func show(_ viewController: UIViewController, isLargeTitle: Bool = false) {
         if let splitViewController {
+            guard !self.contentIsAlreadyDisplayed(viewController, in: splitViewController, for: .secondary) else {
+                return
+            }
             (viewController as? ReaderStreamViewController)?.isNotificationsBarButtonEnabled = true
 
             let navigationVC = UINavigationController(rootViewController: viewController)
@@ -207,6 +210,11 @@ public final class ReaderPresenter: NSObject, SplitViewDisplayable {
             }
             splitViewController.setViewController(navigationVC, for: .secondary)
         } else {
+            // Don't push a view controller on top of another with the same content
+            guard !self.contentIsAlreadyDisplayed(viewController, in: mainNavigationController) else {
+                return
+            }
+
             mainNavigationController.safePushViewController(viewController, animated: true)
         }
     }
@@ -215,14 +223,59 @@ public final class ReaderPresenter: NSObject, SplitViewDisplayable {
     /// the `.secondary` column (split view) or to the main navigation stack.
     private func push(_ viewController: UIViewController) {
         if let splitViewController {
+            // Don't push a view controller on top of another with the same content
+            guard !contentIsAlreadyDisplayed(viewController, in: splitViewController, for: .secondary) else {
+                return
+            }
             let navigationVC = splitViewController.viewController(for: .secondary) as? UINavigationController
             wpAssert(navigationVC != nil)
             navigationVC?.safePushViewController(viewController, animated: true)
         } else {
+            // Don't push a view controller on top of another with the same content
+            guard !self.contentIsAlreadyDisplayed(viewController, in: mainNavigationController) else {
+                return
+            }
+
             mainNavigationController.safePushViewController(viewController, animated: true)
         }
     }
 
+    private func contentIsAlreadyDisplayed(_ viewController: UIViewController, in nav: UINavigationController) -> Bool {
+        if let current = nav.topViewController as? ContentIdentifiable {
+            if let new = viewController as? ContentIdentifiable {
+                if new.contentIdentifier == current.contentIdentifier {
+                    return true
+                }
+            }
+        }
+
+        return false
+    }
+
+    private func contentIsAlreadyDisplayed(
+        _ viewController: UIViewController,
+        in split: UISplitViewController,
+        for column: UISplitViewController.Column
+    ) -> Bool {
+        guard let top = split.viewController(for: column) else {
+            return false
+        }
+
+        if let nav = top as? UINavigationController {
+            return contentIsAlreadyDisplayed(viewController, in: nav)
+        }
+
+        if let current = top as? ContentIdentifiable {
+            if let new = viewController as? ContentIdentifiable {
+                if new.contentIdentifier == current.contentIdentifier {
+                    return true
+                }
+            }
+        }
+
+        return false
+    }
+
     // MARK: - Deep Links (ReaderNavigationPath)
 
     func navigate(to path: ReaderNavigationPath) {

WordPress/Classes/Utility/Universal Links/ContentIdentifiable.swift

@@ -0,0 +1,9 @@
+import Foundation
+
+/// A protocol representing a content identifier – it could be a URL, ISBN, etc
+///
+/// More than one object might share a content identifier – two objects with the same identifier represent the same content.
+///
+public protocol ContentIdentifiable {
+    var contentIdentifier: String? { get }
+}

WordPress/Classes/ViewRelated/Reader/Controllers/ReaderStreamViewController.swift

@@ -1637,6 +1637,24 @@ extension ReaderStreamViewController: UITableViewDelegate, JPScrollViewDelegate
     }
 }
 
+extension ReaderStreamViewController: ContentIdentifiable {
+    var contentIdentifier: String? {
+        if let siteId = self.siteID {
+            return "https://wordpress.com/reader/feeds/\(siteId)/"
+        }
+
+        if let tagSlug = self.tagSlug {
+            return "https://wordpress.com/tag/\(tagSlug)"
+        }
+
+        if let readerTopic {
+            return readerTopic.path
+        }
+
+        return nil
+    }
+}
+
 private enum Strings {
     static let postRemoved = NSLocalizedString("reader.savedPostRemovedNotificationTitle", value: "Saved post removed", comment: "Notification title for when saved post is removed")
 }

WordPress/Classes/ViewRelated/Reader/Detail/ReaderDetailViewController.swift

@@ -1313,3 +1313,14 @@ extension ReaderDetailViewController: BorderedButtonTableViewCellDelegate {
         )
     }
 }
+
+extension ReaderDetailViewController: ContentIdentifiable {
+    var contentIdentifier: String? {
+        // Only ever try to resolve this based on the site ID and post ID – the post object is fetched later
+        if let siteId = self.coordinator?.siteID?.intValue, let postId = self.coordinator?.postID?.intValue {
+            return "https://wordpress.com/reader/feeds/\(siteId)/posts/\(postId)"
+        }
+
+        return nil
+    }
+}