Simplify add saved hashtag toolbar buttons

Closes #522

Tusker/Screens/Explore/AddSavedHashtagViewController.swift

@@ -114,7 +114,63 @@ class AddSavedHashtagViewController: UIViewController, CollectionViewController
     }
     
     private func selectHashtag(_ hashtag: Hashtag) {
-        show(HashtagTimelineViewController(for: hashtag, mastodonController: mastodonController), sender: nil)
+        let vc = HashtagTimelineViewController(for: hashtag, mastodonController: mastodonController)
+        vc.loadViewIfNeeded()
+        
+        let mastodonController = mastodonController!
+        let context = mastodonController.persistentContainer.viewContext
+        let existingSaved = try? context.fetch(SavedHashtag.fetchRequest(name: hashtag.name, account: mastodonController.accountInfo!)).first
+        let saveItem = UIBarButtonItem()
+        func updateSaveItem(saved: Bool) {
+            saveItem.title = saved ? "Unsave Hashag" : "Save Hashtag"
+            saveItem.image = UIImage(systemName: saved ? "minus" : "plus")
+        }
+        saveItem.primaryAction = UIAction(handler: { [unowned self] _ in
+            // re-fetch this in case the button's been tapped before and the captured var would be out of date
+            let existingSaved = try? context.fetch(SavedHashtag.fetchRequest(name: hashtag.name, account: mastodonController.accountInfo!)).first
+            if let existingSaved {
+                context.delete(existingSaved)
+            } else {
+                _ = SavedHashtag(hashtag: hashtag, account: mastodonController.accountInfo!, context: context)
+            }
+            mastodonController.persistentContainer.save(context: context)
+            updateSaveItem(saved: existingSaved == nil)
+            if existingSaved == nil {
+                self.presentingViewController?.dismiss(animated: true)
+            }
+        })
+        // setting primaryAction replace's the bar button's title/image with the action, so do this after
+        updateSaveItem(saved: existingSaved != nil)
+
+        vc.navigationItem.rightBarButtonItems = [
+            saveItem,
+        ]
+        
+        if mastodonController.instanceFeatures.canFollowHashtags {
+            let existingFollowed = mastodonController.followedHashtags.first(where: { $0.name.lowercased() == hashtag.name })
+            let followItem = UIBarButtonItem()
+            func updateFollowItem(followed: Bool) {
+                followItem.title = followed ? "Unfollow Hashtag" : "Follow Hashtag"
+                followItem.image = UIImage(systemName: "person.badge.\(followed ? "minus" : "plus")")
+            }
+            followItem.primaryAction = UIAction(handler: { [unowned self] _ in
+                Task {
+                    let success = await ToggleFollowHashtagService(hashtagName: hashtag.name, presenter: self).toggleFollow()
+                    if success {
+                        let followed = mastodonController.followedHashtags.contains(where: { $0.name.lowercased() == hashtag.name })
+                        updateFollowItem(followed: followed)
+                        if followed {
+                            self.presentingViewController?.dismiss(animated: true)
+                        }
+                    }
+                }
+            })
+            updateFollowItem(followed: existingFollowed != nil)
+
+            vc.navigationItem.rightBarButtonItems!.append(followItem)
+        }
+        
+        show(vc, sender: self)
     }
     
     // MARK: - Interaction
@@ -150,3 +206,7 @@ extension AddSavedHashtagViewController: SearchResultsViewControllerDelegate {
         selectHashtag(hashtag)
     }
 }
+
+extension AddSavedHashtagViewController: TuskerNavigationDelegate {
+    var apiController: MastodonController! { mastodonController }
+}