[frontend/components] Hide virtual scroller ScrollEnd buttons when not needed

Iceshrimp.Frontend/Components/ScrollEnd.razor

@@ -2,7 +2,7 @@
 @using Ljbc1994.Blazor.IntersectionObserver.Components
 @using Iceshrimp.Assets.PhosphorIcons
 <IntersectionObserve OnChange="entry => OnChange(entry)">
-    <div @ref="context.Ref.Current" class="@Class" style="@Style">
+    <div @ref="context.Ref.Current" class="@Class @(Hide ? "hidden" : "")" style="@Style">
         @if (_state is State.Loading or State.Init)
         {
             <LoadingSpinner />
@@ -20,12 +20,15 @@
     [Parameter]                  public string?       Class              { get; set; }
     [Parameter]                  public bool          RequireReset       { get; init; }
     [Parameter]                  public string?       Style              { get; set; }
+    [Parameter]                  public bool          Hide               { get; set; } = false;
+    public                              bool          Visible            { get; private set; }
     private                             State         _state;
 
     private async Task OnChange(IntersectionObserverEntry entry)
     {
         if (entry.IsIntersecting)
         {
+            Visible = true;
             switch (_state)
             {
                 case State.Loading:
@@ -40,6 +43,9 @@
             {
                 _state = State.Waiting;
             }
+        } else if (entry.IsIntersecting == false)
+        {
+            Visible = false;
         }
     }
 

Iceshrimp.Frontend/Components/VirtualScroller.cs

@@ -40,6 +40,7 @@ public class VirtualScroller<T> : ComponentBase, IDisposable where T : IIdentifi
 	private bool  _setScroll    = false;
 	private bool  _shouldRender = false;
 	private bool  _initialized  = false;
+	private bool  _hideBefore   = true;
 
 	private IDisposable? _locationChangeHandlerDisposable;
 
@@ -111,7 +112,8 @@ public class VirtualScroller<T> : ComponentBase, IDisposable where T : IIdentifi
 		builder.AddComponentParameter(3, "ManualLoad", new EventCallback(this, CallbackBeforeAsync));
 		builder.AddComponentParameter(4, "RequireReset", true);
 		builder.AddComponentParameter(5, "Class", "virtual-scroller-button");
-		builder.AddComponentReferenceCapture(6,
+		builder.AddComponentParameter(6, "Hide", _hideBefore);
+		builder.AddComponentReferenceCapture(7,
 											 reference =>
 												 Before = reference as ScrollEnd
 														  ?? throw new InvalidOperationException());
@@ -168,7 +170,18 @@ public class VirtualScroller<T> : ComponentBase, IDisposable where T : IIdentifi
 		}
 		
 		var heightBefore = _module.Invoke<float>("GetDocumentHeight");
-		var res          = await ItemProvider(DirectionEnum.Newer, Items.First().Value);
+		var resTask          = ItemProvider(DirectionEnum.Newer, Items.First().Value);
+		// Only show the spinner if ItemProvider takes more than 500ms to load, and the spinner is actually visible on screen.
+		await Task.WhenAny(Task.Delay(TimeSpan.FromMilliseconds(500)), resTask);
+		if (resTask.IsCompleted == false)
+		{
+			if (Before.Visible)
+			{
+				_hideBefore = false;
+				ReRender();
+			}
+		}
+		var res = await resTask;
 		if (res is not null && res.Count > 0)
 		{
 			foreach (var el in res)
@@ -183,6 +196,12 @@ public class VirtualScroller<T> : ComponentBase, IDisposable where T : IIdentifi
 			var scroll      = _module.Invoke<float>("GetScrollY");
 			_module.InvokeVoid("SetScrollY", scroll + diff);
 		}
+		else if (res?.Count == 0)
+		{
+			_hideBefore = true;
+			Logger.LogInformation("Hiding before");
+			ReRender();
+		}
 
 		Before.Reset();
 	}
@@ -195,6 +214,7 @@ public class VirtualScroller<T> : ComponentBase, IDisposable where T : IIdentifi
 			var add = Items.TryAdd(item.Id, item);
 			if (add is false) Logger.LogError($"Duplicate notification: {item.Id}");
 		}
+
 		ReRender();
 	}
 

Iceshrimp.Frontend/wwwroot/css/app.css

@@ -115,6 +115,7 @@ button {
     padding-inline: 1em;
     align-items: center;
 }
+
 .button:hover {
     background-color: var(--hover-color);
 }
@@ -304,8 +305,25 @@ pre:has(code){
     flex-direction: column;
     align-items: center;
     height: 3rem;
+    transition: height ease-out 250ms;
 }
 
+.virtual-scroller-button.hidden {
+    height: 0;
+    overflow: clip;
+    /*transition: height ease-out 250ms;*/
+    opacity: 0;
+}
+
+/*@Is supported in all browsers*/
+/*noinspection CssInvalidAtRule*/
+@starting-style {
+    .virtual-scroller-button {
+        height: 0;
+    }
+}
+
+
 @keyframes spinner {
     0% {
         rotate: 0deg;
@@ -330,6 +348,7 @@ pre:has(code){
 .lazy-component-target-internal {
     min-height: var(--height);
 }
+
 /*@Is supported in all browsers*/
 /*noinspection CssInvalidAtRule*/
 @starting-style {