Improve splitter UX: visual feedback & smoother resizing

Enhanced the editor's vertical splitter with immediate visual feedback during dragging, including dynamic width, shadow, and handle size. Updated logic to re-render UI and save split ratio in real time. Refined save status updates to reduce unnecessary renders. Improved mobile responsiveness and overall user experience.

Notemark/Components/Pages/Editor.razor

@@ -82,7 +82,7 @@
         <!-- Simple Splitter -->
         @if (showPreview)
         {
-            <div class="splitter" @onmousedown="OnSplitterMouseDown" @onmousedown:preventDefault="true">
+            <div class="splitter @(isDragging ? "dragging" : "")" @onmousedown="OnSplitterMouseDown" @onmousedown:preventDefault="true">
                 <div class="splitter-handle"></div>
             </div>
         }
@@ -156,11 +156,11 @@
             await InvokeAsync(async () => await AutoSave());
         }, null, 2000, Timeout.Infinite); // Increased to 2 seconds for production
         
-        // Don't show "Saving..." immediately, wait for actual save
+        // Only update status if it was previously "Saved"
         if (saveStatus == "Saved")
         {
             saveStatus = "Modified";
-            await InvokeAsync(StateHasChanged);
+            StateHasChanged();
         }
     }
 
@@ -177,9 +177,11 @@
         if (string.IsNullOrEmpty(sessionId) || !hasUnsavedChanges)
             return;
 
+        var previousStatus = saveStatus;
+        
         // Set saving status only when actually starting to save
         saveStatus = "Saving...";
-        await InvokeAsync(StateHasChanged);
+        StateHasChanged(); // Use StateHasChanged instead of InvokeAsync
             
         try
         {
@@ -194,7 +196,7 @@
         catch (OperationCanceledException)
         {
             saveStatus = "Timeout";
-            // Retry after 5 seconds
+            // Simplified retry - no immediate re-rendering
             _ = Task.Delay(5000).ContinueWith(async _ => 
             {
                 if (hasUnsavedChanges)
@@ -206,7 +208,7 @@
         catch (Exception)
         {
             saveStatus = "Error";
-            // Retry after 3 seconds  
+            // Simplified retry - no immediate re-rendering
             _ = Task.Delay(3000).ContinueWith(async _ => 
             {
                 if (hasUnsavedChanges)
@@ -216,7 +218,11 @@
             });
         }
         
-        await InvokeAsync(StateHasChanged);
+        // Only trigger re-render if status actually changed
+        if (saveStatus != previousStatus)
+        {
+            StateHasChanged();
+        }
     }
 
     private void TogglePreview()
@@ -396,25 +402,33 @@
     {
         if (!isDragging || containerWidth <= 0) return;
         
-        var newRatio = clientX / containerWidth;
-        splitRatio = Math.Max(0.2, Math.Min(0.8, newRatio)); // Clamp between 20% and 80%
+        var newRatio = Math.Max(0.2, Math.Min(0.8, clientX / containerWidth)); // Clamp between 20% and 80%
         
-        // Save to localStorage
+        // Update immediately for smooth dragging
+        splitRatio = newRatio;
+        
+        // Use StateHasChanged for immediate visual feedback
+        StateHasChanged();
+    }
+
+    [JSInvokable]
+    public async Task StopDragging()
+    {
+        if (!isDragging) return;
+        
+        isDragging = false;
+        
+        // Save split ratio to localStorage when dragging stops
         try
         {
-            await JSRuntime.InvokeVoidAsync("localStorage.setItem", "notemark-split-ratio", splitRatio.ToString());
+            await JSRuntime.InvokeVoidAsync("localStorage.setItem", "notemark-split-ratio", splitRatio.ToString("F2"));
         }
         catch
         {
             // Ignore localStorage errors
         }
         
+        // Single StateHasChanged at the end
         StateHasChanged();
     }
-
-    [JSInvokable]
-    public void StopDragging()
-    {
-        isDragging = false;
-    }
 }

Notemark/Components/Pages/Editor.razor.css

@@ -438,11 +438,18 @@
   justify-content: center;
   position: relative;
   flex-shrink: 0;
-  transition: background-color 0.2s ease;
+  transition: all 0.15s ease;
 }
 
 .splitter:hover {
   background-color: var(--accent);
+  width: 10px;
+}
+
+.splitter.dragging {
+  background-color: var(--accent);
+  width: 12px;
+  box-shadow: 0 0 8px rgba(0, 122, 204, 0.3);
 }
 
 .splitter-handle {
@@ -450,11 +457,19 @@
   height: 40px;
   background-color: var(--secondary-text);
   border-radius: 1px;
-  transition: background-color 0.2s ease;
+  transition: all 0.15s ease;
 }
 
 .splitter:hover .splitter-handle {
   background-color: white;
+  width: 3px;
+  height: 50px;
+}
+
+.splitter.dragging .splitter-handle {
+  background-color: white;
+  width: 4px;
+  height: 60px;
 }
 
 /* Mobile Responsive - Place at end to override desktop styles */

Notemark/wwwroot/js/theme.js

@@ -59,9 +59,15 @@ window.startSplitterDrag = function(blazorInstance) {
     document.addEventListener('mousemove', handleSplitterMove);
     document.addEventListener('mouseup', handleSplitterUp);
     
-    // Prevent text selection
+    // Improve visual feedback during drag
     document.body.style.userSelect = 'none';
     document.body.style.cursor = 'col-resize';
+    
+    // Add dragging class for visual feedback
+    const splitter = document.querySelector('.splitter');
+    if (splitter) {
+        splitter.classList.add('dragging');
+    }
 };
 
 function handleSplitterMove(e) {
@@ -88,6 +94,12 @@ function handleSplitterUp(e) {
     document.body.style.cursor = '';
     document.body.style.userSelect = '';
     
+    // Remove dragging visual state
+    const splitter = document.querySelector('.splitter');
+    if (splitter) {
+        splitter.classList.remove('dragging');
+    }
+    
     // Notify Blazor that dragging stopped
     if (splitterState.blazorInstance) {
         splitterState.blazorInstance.invokeMethodAsync('StopDragging');