From 11d4d20873389c9205af7be83ac6946737aa32c4 Mon Sep 17 00:00:00 2001
From: Thomas Ricouard <ricouard77@gmail.com>
Date: Sun, 25 Dec 2022 18:43:15 +0100
Subject: [PATCH] Timeline scroll to top UX / Flow

---
 .../Sources/Timeline/TimelineView.swift       | 36 +++++++++++++++----
 .../Sources/Timeline/TimelineViewModel.swift  | 11 ++++--
 2 files changed, 39 insertions(+), 8 deletions(-)

diff --git a/Packages/Timeline/Sources/Timeline/TimelineView.swift b/Packages/Timeline/Sources/Timeline/TimelineView.swift
index 26c39019..baeb0fe8 100644
--- a/Packages/Timeline/Sources/Timeline/TimelineView.swift
+++ b/Packages/Timeline/Sources/Timeline/TimelineView.swift
@@ -18,13 +18,21 @@ public struct TimelineView: View {
   }
   
   public var body: some View {
-    ScrollView {
-      LazyVStack {
-        tagHeaderView
-          .padding(.bottom, 16)
-        StatusesListView(fetcher: viewModel)
+    ScrollViewReader { proxy in
+      ZStack(alignment: .top) {
+        ScrollView {
+          LazyVStack {
+            tagHeaderView
+              .padding(.bottom, 16)
+              .id("top")
+            StatusesListView(fetcher: viewModel)
+          }
+          .padding(.top, DS.Constants.layoutPadding)
+        }
+        if filter == .home {
+          makePendingNewPostsView(proxy: proxy)
+        }
       }
-      .padding(.top, DS.Constants.layoutPadding)
     }
     .navigationTitle(filter?.title() ?? viewModel.timeline.title())
     .navigationBarTitleDisplayMode(.inline)
@@ -53,6 +61,22 @@ public struct TimelineView: View {
     }
   }
   
+  @ViewBuilder
+  private func makePendingNewPostsView(proxy: ScrollViewProxy) -> some View {
+    if !viewModel.pendingStatuses.isEmpty {
+      Button {
+        proxy.scrollTo("top")
+        viewModel.displayPendingStatuses()
+      } label: {
+        Text("\(viewModel.pendingStatuses.count) new posts")
+      }
+      .buttonStyle(.bordered)
+      .background(.thinMaterial)
+      .cornerRadius(8)
+      .padding(.top, 6)
+    }
+  }
+  
   @ViewBuilder
   private var tagHeaderView: some View {
     if let tag = viewModel.tag {
diff --git a/Packages/Timeline/Sources/Timeline/TimelineViewModel.swift b/Packages/Timeline/Sources/Timeline/TimelineViewModel.swift
index 29041bbd..ac01954d 100644
--- a/Packages/Timeline/Sources/Timeline/TimelineViewModel.swift
+++ b/Packages/Timeline/Sources/Timeline/TimelineViewModel.swift
@@ -27,6 +27,7 @@ class TimelineViewModel: ObservableObject, StatusesFetcher {
     }
   }
   @Published var tag: Tag?
+  @Published var pendingStatuses: [Status] = []
   
   var serverName: String {
     client?.server ?? "Error"
@@ -36,6 +37,7 @@ class TimelineViewModel: ObservableObject, StatusesFetcher {
     guard let client else { return }
     do {
       if statuses.isEmpty {
+        pendingStatuses = []
         statusesState = .loading
         statuses = try await client.get(endpoint: timeline.endpoint(sinceId: nil, maxId: nil))
       } else if let first = statuses.first {
@@ -86,11 +88,16 @@ class TimelineViewModel: ObservableObject, StatusesFetcher {
   func handleEvent(event: any StreamEvent) {
     guard timeline == .home else { return }
     if let event = event as? StreamEventUpdate {
-      statuses.insert(event.status, at: 0)
-      statusesState = .display(statuses: statuses, nextPageState: .hasNextPage)
+      pendingStatuses.insert(event.status, at: 0)
     } else if let event = event as? StreamEventDelete {
       statuses.removeAll(where: { $0.id == event.status })
       statusesState = .display(statuses: statuses, nextPageState: .hasNextPage)
     }
   }
+  
+  func displayPendingStatuses() {
+    statuses.insert(contentsOf: pendingStatuses, at: 0)
+    pendingStatuses = []
+    statusesState = .display(statuses: statuses, nextPageState: .hasNextPage)
+  }
 }