iOS: Make shift-space scroll up even when the detail view doesn't have focus

iOS/Article/ArticleViewController.swift

@@ -293,10 +293,18 @@ class ArticleViewController: UIViewController {
 		return currentWebViewController?.canScrollDown() ?? false
 	}
 
+	func canScrollUp() -> Bool {
+		return currentWebViewController?.canScrollUp() ?? false
+	}
+
 	func scrollPageDown() {
 		currentWebViewController?.scrollPageDown()
 	}
 
+	func scrollPageUp() {
+		currentWebViewController?.scrollPageUp()
+	}
+	
 	func stopArticleExtractorIfProcessing() {
 		currentWebViewController?.stopArticleExtractorIfProcessing()
 	}

iOS/Article/WebViewController.swift

@@ -123,17 +123,23 @@ class WebViewController: UIViewController {
 
 	func canScrollDown() -> Bool {
 		guard let webView = webView else { return false }
-		return webView.scrollView.contentOffset.y < finalScrollPosition()
+		return webView.scrollView.contentOffset.y < finalScrollPosition(scrollingUp: false)
 	}
 
-	func scrollPageDown() {
+	func canScrollUp() -> Bool {
+		guard let webView = webView else { return false }
+		return webView.scrollView.contentOffset.y > finalScrollPosition(scrollingUp: true)
+	}
+
+	private func scrollPage(up scrollingUp: Bool) {
 		guard let webView = webView else { return }
 
 		let overlap = 2 * UIFont.systemFont(ofSize: UIFont.systemFontSize).lineHeight * UIScreen.main.scale
 		let scrollToY: CGFloat = {
-			let fullScroll = webView.scrollView.contentOffset.y + webView.scrollView.layoutMarginsGuide.layoutFrame.height - overlap
-			let final = finalScrollPosition()
-			return fullScroll < final ? fullScroll : final
+			let scrollDistance = webView.scrollView.layoutMarginsGuide.layoutFrame.height - overlap;
+			let fullScroll = webView.scrollView.contentOffset.y + (scrollingUp ? -scrollDistance : scrollDistance)
+			let final = finalScrollPosition(scrollingUp: scrollingUp)
+			return (scrollingUp ? fullScroll > final : fullScroll < final) ? fullScroll : final
 		}()
 
 		let convertedPoint = self.view.convert(CGPoint(x: 0, y: 0), to: webView.scrollView)
@@ -141,6 +147,14 @@ class WebViewController: UIViewController {
 		webView.scrollView.setContentOffset(scrollToPoint, animated: true)
 	}
 
+	func scrollPageDown() {
+		scrollPage(up: false)
+	}
+
+	func scrollPageUp() {
+		scrollPage(up: true)
+	}
+
 	func hideClickedImage() {
 		webView?.evaluateJavaScript("hideClickedImage();")
 	}
@@ -539,9 +553,14 @@ private extension WebViewController {
 		
 	}
 	
-	func finalScrollPosition() -> CGFloat {
+	func finalScrollPosition(scrollingUp: Bool) -> CGFloat {
 		guard let webView = webView else { return 0 }
-		return webView.scrollView.contentSize.height - webView.scrollView.bounds.height + webView.scrollView.safeAreaInsets.bottom
+
+		if scrollingUp {
+			return -webView.scrollView.safeAreaInsets.top
+		} else {
+			return webView.scrollView.contentSize.height - webView.scrollView.bounds.height + webView.scrollView.safeAreaInsets.bottom
+		}
 	}
 	
 	func startArticleExtractor() {

iOS/RootSplitViewController.swift

@@ -36,6 +36,10 @@ class RootSplitViewController: UISplitViewController {
 		coordinator.scrollOrGoToNextUnread()
 	}
 
+	@objc func scrollUp(_ sender: Any?) {
+		coordinator.scrollUp()
+	}
+	
 	@objc func goToPreviousUnread(_ sender: Any?) {
 		coordinator.selectPrevUnread()
 	}

iOS/SceneCoordinator.swift

@@ -991,6 +991,12 @@ class SceneCoordinator: NSObject, UndoableCommandRunner, UnreadCountProvider {
 		}
 	}
 
+	func scrollUp() {
+		if articleViewController?.canScrollUp() ?? false {
+			articleViewController?.scrollPageUp()
+		}
+	}
+	
 	func markAllAsRead(_ articles: [Article]) {
 		markArticlesWithUndo(articles, statusKey: .read, flag: true)
 	}