From 2292d04f918403fa2d7296157caa044b3fbce258 Mon Sep 17 00:00:00 2001
From: Maurice Parker <mo@vincode.io>
Date: Thu, 2 Jul 2020 17:36:50 -0500
Subject: [PATCH] Revert to using List for timeline and use infinite scrolling
 technique to speed up timeline loads

---
 .../Shared/Timeline/TimelineItemView.swift    |  1 -
 .../Shared/Timeline/TimelineModel.swift       | 21 ++++++++++++++++---
 .../Shared/Timeline/TimelineView.swift        |  9 ++++----
 3 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/Multiplatform/Shared/Timeline/TimelineItemView.swift b/Multiplatform/Shared/Timeline/TimelineItemView.swift
index 62c7dfaad..d4f4f172a 100644
--- a/Multiplatform/Shared/Timeline/TimelineItemView.swift
+++ b/Multiplatform/Shared/Timeline/TimelineItemView.swift
@@ -45,7 +45,6 @@ struct TimelineItemView: View {
 					}
 				}
 			}
-			Divider()
 		}
 		.onAppear {
 			articleIconImageLoader.loadImage(for: timelineItem.article)
diff --git a/Multiplatform/Shared/Timeline/TimelineModel.swift b/Multiplatform/Shared/Timeline/TimelineModel.swift
index d89da96a1..307bf0f03 100644
--- a/Multiplatform/Shared/Timeline/TimelineModel.swift
+++ b/Multiplatform/Shared/Timeline/TimelineModel.swift
@@ -55,6 +55,14 @@ class TimelineModel: ObservableObject {
 		fetchAndReplaceArticlesAsync()
 	}
 	
+	// TODO: Replace this with ScrollViewReader if we have to keep it
+	func loadMoreTimelineItemsIfNecessary(_ timelineItem: TimelineItem) {
+		let thresholdIndex = timelineItems.index(timelineItems.endIndex, offsetBy: -10)
+		if timelineItems.firstIndex(where: { $0.id == timelineItem.id }) == thresholdIndex {
+			nextBatch()
+		}
+	}
+	
 }
 
 // MARK: Private
@@ -112,12 +120,19 @@ private extension TimelineModel {
 	
 	func replaceArticles(with unsortedArticles: Set<Article>) {
 		articles = Array(unsortedArticles).sortedByDate(sortDirection ? .orderedDescending : .orderedAscending, groupByFeed: groupByFeed)
-		timelineItems = articles.map { TimelineItem(article: $0) }
-		
+		timelineItems = [TimelineItem]()
+		nextBatch()
 		// TODO: Update unread counts and other item done in didSet on AppKit
 	}
 
-
+	func nextBatch() {
+		let rangeEndIndex = timelineItems.endIndex + 50 > articles.endIndex ? articles.endIndex : timelineItems.endIndex + 50
+		let range = timelineItems.endIndex..<rangeEndIndex
+		for i in range {
+			timelineItems.append(TimelineItem(article: articles[i]))
+		}
+	}
+	
 	// MARK: - Notifications
 
 }
diff --git a/Multiplatform/Shared/Timeline/TimelineView.swift b/Multiplatform/Shared/Timeline/TimelineView.swift
index 1989e5ea5..8711b1cf5 100644
--- a/Multiplatform/Shared/Timeline/TimelineView.swift
+++ b/Multiplatform/Shared/Timeline/TimelineView.swift
@@ -13,12 +13,11 @@ struct TimelineView: View {
 	@EnvironmentObject private var timelineModel: TimelineModel
 
 	var body: some View {
-		ScrollView {
-			LazyVStack() {
-				ForEach(timelineModel.timelineItems) { timelineItem in
-					TimelineItemView(timelineItem: timelineItem)
+		List(timelineModel.timelineItems) { timelineItem in
+			TimelineItemView(timelineItem: timelineItem)
+				.onAppear {
+					timelineModel.loadMoreTimelineItemsIfNecessary(timelineItem)
 				}
-			}
 		}
     }