fix(editor): prevent recursive selection updates

Sources/SaplingEditor/HybridMarkdownEditor.swift

@@ -37,10 +37,12 @@ public final class HybridMarkdownEditorViewModel: ObservableObject, EditorCoordi
     }
 
     public func updateSource(_ source: String) {
+        guard state.document.source != source else { return }
         state.updateSource(source)
     }
 
     public func updateSelection(_ selection: EditorSelection) {
+        guard state.selection != selection else { return }
         state.updateSelection(selection)
     }
 
@@ -172,13 +174,15 @@ private struct NativeMarkdownTextView: NSViewRepresentable {
         guard let textView = scrollView.documentView as? NSTextView else { return }
 
         if textView.string != text {
+            context.coordinator.performProgrammaticUpdate {
                 textView.string = text
             }
+        }
 
         let selectedRange = selection.range
         if textView.selectedRange() != selectedRange,
            selectedRange.location <= textView.string.utf16.count {
-            textView.setSelectedRange(selectedRange)
+            context.coordinator.setSelection(selectedRange, in: textView)
         }
 
         context.coordinator.applyHybridAttributes(to: textView)
@@ -186,32 +190,39 @@ private struct NativeMarkdownTextView: NSViewRepresentable {
 
     final class Coordinator: NSObject, NSTextViewDelegate {
         var parent: NativeMarkdownTextView
-        private var isApplyingAttributes = false
+        private var programmaticUpdateDepth = 0
+        private var lastStyledText: String?
+        private var lastStyledActiveLineIndex: Int?
 
         init(_ parent: NativeMarkdownTextView) {
             self.parent = parent
         }
 
         func textDidChange(_ notification: Notification) {
-            guard !isApplyingAttributes,
+            guard !isPerformingProgrammaticUpdate else { return }
-                  let textView = notification.object as? NSTextView
+            guard let textView = notification.object as? NSTextView else { return }
-            else { return }
 
             parent.text = textView.string
             parent.selection = EditorSelection(range: textView.selectedRange())
+            lastStyledText = nil
             applyHybridAttributes(to: textView)
         }
 
         func textViewDidChangeSelection(_ notification: Notification) {
+            guard !isPerformingProgrammaticUpdate else { return }
             guard let textView = notification.object as? NSTextView else { return }
-            parent.selection = EditorSelection(range: textView.selectedRange())
+            let newSelection = EditorSelection(range: textView.selectedRange())
+            guard parent.selection != newSelection else { return }
             applyHybridAttributes(to: textView)
+            parent.selection = newSelection
         }
 
         func applyHybridAttributes(to textView: NSTextView) {
             guard let textStorage = textView.textStorage else { return }
-            isApplyingAttributes = true
+            guard shouldRestyle(textView.string) else { return }
+
             let selectedRange = textView.selectedRange()
+            performProgrammaticUpdate {
                 MarkdownTextStyler.apply(
                     to: textStorage,
                     activeLineIndex: parent.activeLineIndex,
@@ -221,8 +232,37 @@ private struct NativeMarkdownTextView: NSViewRepresentable {
                     secondaryTextColor: .secondaryLabelColor,
                     accentColor: .controlAccentColor
                 )
+                if textView.selectedRange() != selectedRange,
+                   selectedRange.location <= textView.string.utf16.count {
                     textView.setSelectedRange(selectedRange)
-            isApplyingAttributes = false
+                }
+            }
+
+            lastStyledText = textView.string
+            lastStyledActiveLineIndex = parent.activeLineIndex
+        }
+
+        func setSelection(_ range: NSRange, in textView: NSTextView) {
+            guard textView.selectedRange() != range else { return }
+            performProgrammaticUpdate {
+                textView.setSelectedRange(range)
+            }
+        }
+
+        func performProgrammaticUpdate(_ updates: () -> Void) {
+            programmaticUpdateDepth += 1
+            defer {
+                programmaticUpdateDepth -= 1
+            }
+            updates()
+        }
+
+        private var isPerformingProgrammaticUpdate: Bool {
+            programmaticUpdateDepth > 0
+        }
+
+        private func shouldRestyle(_ text: String) -> Bool {
+            lastStyledText != text || lastStyledActiveLineIndex != parent.activeLineIndex
         }
     }
 }
@@ -254,34 +294,44 @@ private struct NativeMarkdownTextView: UIViewRepresentable {
     func updateUIView(_ textView: UITextView, context: Context) {
         context.coordinator.parent = self
         if textView.text != text {
+            context.coordinator.performProgrammaticUpdate {
                 textView.text = text
             }
+        }
         context.coordinator.applyHybridAttributes(to: textView)
     }
 
     final class Coordinator: NSObject, UITextViewDelegate {
         var parent: NativeMarkdownTextView
-        private var isApplyingAttributes = false
+        private var programmaticUpdateDepth = 0
+        private var lastStyledText: String?
+        private var lastStyledActiveLineIndex: Int?
 
         init(_ parent: NativeMarkdownTextView) {
             self.parent = parent
         }
 
         func textViewDidChange(_ textView: UITextView) {
-            guard !isApplyingAttributes else { return }
+            guard !isPerformingProgrammaticUpdate else { return }
             parent.text = textView.text
             parent.selection = EditorSelection(range: textView.selectedRange)
+            lastStyledText = nil
             applyHybridAttributes(to: textView)
         }
 
         func textViewDidChangeSelection(_ textView: UITextView) {
-            parent.selection = EditorSelection(range: textView.selectedRange)
+            guard !isPerformingProgrammaticUpdate else { return }
+            let newSelection = EditorSelection(range: textView.selectedRange)
+            guard parent.selection != newSelection else { return }
             applyHybridAttributes(to: textView)
+            parent.selection = newSelection
         }
 
         func applyHybridAttributes(to textView: UITextView) {
-            isApplyingAttributes = true
+            guard shouldRestyle(textView.text) else { return }
+
             let selectedRange = textView.selectedRange
+            performProgrammaticUpdate {
                 MarkdownTextStyler.apply(
                     to: textView.textStorage,
                     activeLineIndex: parent.activeLineIndex,
@@ -291,8 +341,30 @@ private struct NativeMarkdownTextView: UIViewRepresentable {
                     secondaryTextColor: .secondaryLabel,
                     accentColor: .systemBlue
                 )
+                if textView.selectedRange != selectedRange,
+                   selectedRange.location <= textView.text.utf16.count {
                     textView.selectedRange = selectedRange
-            isApplyingAttributes = false
+                }
+            }
+
+            lastStyledText = textView.text
+            lastStyledActiveLineIndex = parent.activeLineIndex
+        }
+
+        func performProgrammaticUpdate(_ updates: () -> Void) {
+            programmaticUpdateDepth += 1
+            defer {
+                programmaticUpdateDepth -= 1
+            }
+            updates()
+        }
+
+        private var isPerformingProgrammaticUpdate: Bool {
+            programmaticUpdateDepth > 0
+        }
+
+        private func shouldRestyle(_ text: String) -> Bool {
+            lastStyledText != text || lastStyledActiveLineIndex != parent.activeLineIndex
         }
     }
 }