Implement next unread UI functionality.

iOS/Base.lproj/Main.storyboard

@@ -149,7 +149,11 @@
                             </connections>
                         </barButtonItem>
                         <barButtonItem style="plain" systemItem="flexibleSpace" id="93y-8j-WBh"/>
-                        <barButtonItem enabled="NO" title="First Unread" id="2v2-jD-C9k"/>
+                        <barButtonItem enabled="NO" title="First Unread" id="2v2-jD-C9k">
+                            <connections>
+                                <action selector="nextUnread:" destination="Kyk-vK-QRX" id="lwt-VU-zdW"/>
+                            </connections>
+                        </barButtonItem>
                     </toolbarItems>
                     <navigationItem key="navigationItem" title="Timeline" largeTitleDisplayMode="never" id="wcC-1L-ug4"/>
                     <simulatedToolbarMetrics key="simulatedBottomBarMetrics"/>

iOS/Detail/DetailViewController.swift

@@ -55,7 +55,7 @@ class DetailViewController: UIViewController {
 			return
 		}
 		
-		nextArticleBarButtonItem.isEnabled = false
+		nextUnreadBarButtonItem.isEnabled = navState?.isNextUnreadAvailable ?? false
 		prevArticleBarButtonItem.isEnabled = navState?.isPrevArticleAvailable ?? false
 		nextArticleBarButtonItem.isEnabled = navState?.isNextArticleAvailable ?? false
 
@@ -101,6 +101,7 @@ class DetailViewController: UIViewController {
 	// MARK: Actions
 	
 	@IBAction func nextUnread(_ sender: Any) {
+		navState?.selectNextUnread()
 	}
 	
 	@IBAction func prevArticle(_ sender: Any) {

iOS/Master/MasterViewController.swift

@@ -81,8 +81,9 @@ class MasterViewController: UITableViewController, UndoableCommandRunner {
 		if let account = representedObject as? Account {
 			if let node = navState.rootNode.childNodeRepresentingObject(account) {
 				let sectionIndex = navState.rootNode.indexOfChild(node)!
-				let headerView = tableView.headerView(forSection: sectionIndex) as! MasterTableViewSectionHeader
-				headerView.unreadCount = account.unreadCount
+				if let headerView = tableView.headerView(forSection: sectionIndex) as? MasterTableViewSectionHeader {
+					headerView.unreadCount = account.unreadCount
+				}
 			}
 			return
 		}

iOS/NavigationStateController.swift

@@ -61,6 +61,7 @@ class NavigationStateController {
 			if let fetcher = node.representedObject as? ArticleFetcher {
 				timelineFetcher = fetcher
 			}
+			NotificationCenter.default.post(name: .MasterSelectionDidChange, object: self, userInfo: nil)
 		}
 	}
 	
@@ -144,6 +145,10 @@ class NavigationStateController {
 		}
 	}
 	
+	var isNextUnreadAvailable: Bool {
+		return appDelegate.unreadCount > 0
+	}
+	
 	init() {
 
 		for section in treeController.rootNode.childNodes {
@@ -374,8 +379,25 @@ class NavigationStateController {
 		return indexes
 	}
 	
+	func selectNextUnread() {
+		
+		// This should never happen, but I don't want to risk throwing us
+		// into an infinate loop searching for an unread that isn't there.
+		if appDelegate.unreadCount < 1 {
+			return
+		}
+		
+		if selectNextUnreadArticleInTimeline() {
+			return
+		}
+		
+		selectNextUnreadFeedFetcher()
+		selectNextUnreadArticleInTimeline()
+		
+	}
+	
 }
-
+	
 private extension NavigationStateController {
 
 	func rebuildBackingStores() {
@@ -386,6 +408,105 @@ private extension NavigationStateController {
 		}
 	}
 	
+	func updateShowAvatars() {
+		
+		if showFeedNames {
+			self.showAvatars = true
+			return
+		}
+		
+		for article in articles {
+			if let authors = article.authors {
+				for author in authors {
+					if author.avatarURL != nil {
+						self.showAvatars = true
+						return
+					}
+				}
+			}
+		}
+		
+		self.showAvatars = false
+	}
+	
+	// MARK: Select Next Unread
+
+	@discardableResult
+	func selectNextUnreadArticleInTimeline() -> Bool {
+		
+		let startingRow: Int = {
+			if let indexPath = currentArticleIndexPath {
+				return indexPath.row
+			} else {
+				return 0
+			}
+		}()
+		
+		for i in startingRow..<articles.count {
+			let article = articles[i]
+			if !article.status.read {
+				currentArticleIndexPath = IndexPath(row: i, section: 0)
+				return true
+			}
+		}
+		
+		return false
+		
+	}
+	
+	func selectNextUnreadFeedFetcher() {
+		
+		guard let indexPath = currentMasterIndexPath else {
+			assertionFailure()
+			return
+		}
+		
+		// Increment or wrap around the IndexPath
+		let nextIndexPath: IndexPath = {
+			if indexPath.row + 1 >= shadowTable[indexPath.section].count {
+				if indexPath.section + 1 >= shadowTable.count {
+					return IndexPath(row: 0, section: 0)
+				} else {
+					return IndexPath(row: 0, section: indexPath.section + 1)
+				}
+			} else {
+				return IndexPath(row: indexPath.row + 1, section: indexPath.section)
+			}
+		}()
+		
+		if selectNextUnreadFeedFetcher(startingWith: nextIndexPath) {
+			return
+		}
+		selectNextUnreadFeedFetcher(startingWith: IndexPath(row: 0, section: 0))
+		
+	}
+	
+	@discardableResult
+	func selectNextUnreadFeedFetcher(startingWith indexPath: IndexPath) -> Bool {
+		
+		for i in indexPath.section..<shadowTable.count {
+			
+			for j in indexPath.row..<shadowTable[indexPath.section].count {
+				
+				let nextIndexPath = IndexPath(row: j, section: i)
+				guard let node = nodeFor(nextIndexPath), let unreadCountProvider = node.representedObject as? UnreadCountProvider else {
+					assertionFailure()
+					return true
+				}
+				
+				if unreadCountProvider.unreadCount > 0 {
+					currentMasterIndexPath = nextIndexPath
+					return true
+				}
+				
+			}
+			
+		}
+		
+		return false
+		
+	}
+	
 	// MARK: Fetching Articles
 	
 	func fetchArticles() {
@@ -486,32 +607,9 @@ private extension NavigationStateController {
 				}
 			}
 		}
-
+		
 		return false
 		
 	}
-
-	// MARK: Misc
-	
-	func updateShowAvatars() {
-		
-		if showFeedNames {
-			self.showAvatars = true
-			return
-		}
-		
-		for article in articles {
-			if let authors = article.authors {
-				for author in authors {
-					if author.avatarURL != nil {
-						self.showAvatars = true
-						return
-					}
-				}
-			}
-		}
-		
-		self.showAvatars = false
-	}
 	
 }

iOS/Timeline/MasterTimelineViewController.swift

@@ -54,7 +54,7 @@ class MasterTimelineViewController: UITableViewController, UndoableCommandRunner
 			changeToDisplayMode(splitViewController.displayMode)
 		}
 		
-		reloadUI()
+		resetUI()
 		
 	}
 	
@@ -107,6 +107,10 @@ class MasterTimelineViewController: UITableViewController, UndoableCommandRunner
 		
 	}
 	
+	@IBAction func nextUnread(_ sender: Any) {
+		navState?.selectNextUnread()
+	}
+	
 	// MARK: - Table view
 
     override func numberOfSections(in tableView: UITableView) -> Int {
@@ -251,7 +255,7 @@ class MasterTimelineViewController: UITableViewController, UndoableCommandRunner
 	}
 
 	@objc func articlesReinitialized(_ note: Notification) {
-		reloadUI()
+		resetUI()
 	}
 	
 	@objc func articleDataDidChange(_ note: Notification) {
@@ -270,6 +274,8 @@ class MasterTimelineViewController: UITableViewController, UndoableCommandRunner
 			}
 		}
 		
+		reloadUI()
+		
 	}
 
 	// MARK: Reloading
@@ -350,6 +356,7 @@ private extension MasterTimelineViewController {
 	}
 
 	func changeToDisplayMode(_ displayMode: UISplitViewController.DisplayMode) {
+		
 		if displayMode == .allVisible {
 			nextUnreadButton.isEnabled = false
 			nextUnreadButton.title = ""
@@ -357,9 +364,12 @@ private extension MasterTimelineViewController {
 			nextUnreadButton.isEnabled = false
 			nextUnreadButton.title = NSLocalizedString("First Unread", comment: "First Unread")
 		}
+		
+		reloadUI()
+		
 	}
 	
-	func reloadUI() {
+	func resetUI() {
 		
 		updateTableViewRowHeight()
 		title = navState?.timelineName
@@ -368,6 +378,15 @@ private extension MasterTimelineViewController {
 			tableView.scrollToRow(at: IndexPath(row: 0, section: 0), at: .top, animated: false)
 		}
 		
+		reloadUI()
+		
+	}
+	
+	func reloadUI() {
+		// Since there is no hidden property on a bar button item, we just hide its title
+		if !(nextUnreadButton.title?.isEmpty ?? true) {
+			nextUnreadButton.isEnabled = navState?.isNextUnreadAvailable ?? false
+		}
 	}
 	
 	func configureTimelineCell(_ cell: MasterTimelineTableViewCell, article: Article) {