From 3fdf8b3728b62c41f4357fd690e0c716bf5fe34e Mon Sep 17 00:00:00 2001
From: Brent Simmons <brent@ranchero.com>
Date: Wed, 26 Sep 2018 21:33:55 -0700
Subject: [PATCH] Improve scrolling performance with very large timelines.
 Reload visible cells only, and minimize the amount of looping through
 articles in the array.

---
 .../MainWindow/Timeline/ArticleArray.swift    | 30 --------------
 .../Timeline/TimelineViewController.swift     | 39 +++++++++++++------
 2 files changed, 27 insertions(+), 42 deletions(-)

diff --git a/NetNewsWire/MainWindow/Timeline/ArticleArray.swift b/NetNewsWire/MainWindow/Timeline/ArticleArray.swift
index b9b7b4076..575e70d0b 100644
--- a/NetNewsWire/MainWindow/Timeline/ArticleArray.swift
+++ b/NetNewsWire/MainWindow/Timeline/ArticleArray.swift
@@ -50,20 +50,6 @@ extension Array where Element == Article {
 		})
 	}
 
-	func indexesForArticleIDs(_ articleIDs: Set<String>) -> IndexSet {
-
-		var indexes = IndexSet()
-
-		articleIDs.forEach { (articleID) in
-			let oneIndex = rowForArticleID(articleID)
-			if oneIndex != NSNotFound {
-				indexes.insert(oneIndex)
-			}
-		}
-
-		return indexes
-	}
-
 	func sortedByDate(_ sortDirection: ComparisonResult) -> ArticleArray {
 
 		let articles = sorted { (article1, article2) -> Bool in
@@ -118,19 +104,3 @@ extension Array where Element == Article {
 	}
 }
 
-private extension Array where Element == Article {
-
-	func rowForArticleID(_ articleID: String) -> Int {
-
-		if let index = index(where: { $0.articleID == articleID }) {
-			return index
-		}
-
-		return NSNotFound
-	}
-
-	func rowForArticle(_ article: Article) -> Int {
-
-		return rowForArticleID(article.articleID)
-	}
-}
diff --git a/NetNewsWire/MainWindow/Timeline/TimelineViewController.swift b/NetNewsWire/MainWindow/Timeline/TimelineViewController.swift
index a46e97e44..bdd06e929 100644
--- a/NetNewsWire/MainWindow/Timeline/TimelineViewController.swift
+++ b/NetNewsWire/MainWindow/Timeline/TimelineViewController.swift
@@ -361,7 +361,7 @@ class TimelineViewController: NSViewController, UndoableCommandRunner {
 		guard let articles = note.userInfo?[Account.UserInfoKey.articles] as? Set<Article> else {
 			return
 		}
-		reloadCellsForArticleIDs(articles.articleIDs())
+		reloadVisibleCells(for: articles)
 	}
 
 	@objc func feedIconDidBecomeAvailable(_ note: Notification) {
@@ -369,10 +369,15 @@ class TimelineViewController: NSViewController, UndoableCommandRunner {
 		guard let feed = note.userInfo?[UserInfoKey.feed] as? Feed else {
 			return
 		}
-		let articlesToReload = articles.filter { (article) -> Bool in
+		let indexesToReload = tableView.indexesOfAvailableRowsPassingTest { (row) -> Bool in
+			guard let article = articles.articleAtRow(row) else {
+				return false
+			}
 			return feed == article.feed
 		}
-		reloadCellsForArticles(articlesToReload)
+		if let indexesToReload = indexesToReload {
+			reloadCells(for: indexesToReload)
+		}
 	}
 
 	@objc func avatarDidBecomeAvailable(_ note: Notification) {
@@ -432,22 +437,32 @@ class TimelineViewController: NSViewController, UndoableCommandRunner {
 		return nil
 	}
 	
-	private func reloadCellsForArticles(_ articles: [Article]) {
-		
-		reloadCellsForArticleIDs(Set(articles.articleIDs()))
+	private func reloadVisibleCells(for articles: [Article]) {
+		reloadVisibleCells(for: Set(articles.articleIDs()))
+	}
+
+	private func reloadVisibleCells(for articles: Set<Article>) {
+		reloadVisibleCells(for: articles.articleIDs())
 	}
 	
-	private func reloadCellsForArticleIDs(_ articleIDs: Set<String>) {
-
+	private func reloadVisibleCells(for articleIDs: Set<String>) {
 		if articleIDs.isEmpty {
 			return
 		}
-		let indexes = articles.indexesForArticleIDs(articleIDs)
-		reloadCells(for: indexes)
+		let indexes = indexesForArticleIDs(articleIDs)
+		reloadVisibleCells(for: indexes)
+	}
+
+	private func reloadVisibleCells(for indexes: IndexSet) {
+		let indexesToReload = tableView.indexesOfAvailableRowsPassingTest { (row) -> Bool in
+			return indexes.contains(row)
+		}
+		if let indexesToReload = indexesToReload {
+			reloadCells(for: indexesToReload)
+		}
 	}
 
 	private func reloadCells(for indexes: IndexSet) {
-
 		if indexes.isEmpty {
 			return
 		}
@@ -776,7 +791,7 @@ private extension TimelineViewController {
 
 	func selectArticles(_ articleIDs: [String]) {
 
-		let indexesToSelect = articles.indexesForArticleIDs(Set(articleIDs))
+		let indexesToSelect = indexesForArticleIDs(Set(articleIDs))
 		if indexesToSelect.isEmpty {
 			tableView.deselectAll(self)
 			return