From f1276bdcec5f270cee83b72fb38837e2ea9f8cf8 Mon Sep 17 00:00:00 2001
From: Khan Winter <35942988+thecoolwinter@users.noreply.github.com>
Date: Tue, 8 Apr 2025 11:53:11 -0500
Subject: [PATCH 1/8] Move Text Layout, Selection Edits to Storage Delegates

---
 .../TextLayoutManager+Edits.swift             | 94 +++++++++++--------
 .../TextLayoutManager+Public.swift            | 11 ++-
 .../TextLayoutManager+Transaction.swift       | 38 --------
 .../TextLayoutManager+ensureLayout.swift      |  7 +-
 .../TextLayoutManager/TextLayoutManager.swift | 14 +--
 .../TextSelectionManager+Update.swift         | 30 +++---
 .../TextView/TextView+ReplaceCharacters.swift |  4 -
 .../CodeEditTextView/TextView/TextView.swift  |  3 +-
 .../Utils/CEUndoManager.swift                 | 10 +-
 9 files changed, 96 insertions(+), 115 deletions(-)
 delete mode 100644 Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Transaction.swift

diff --git a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Edits.swift b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Edits.swift
index 8219bf162..968e7389d 100644
--- a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Edits.swift
+++ b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Edits.swift
@@ -10,17 +10,50 @@ import AppKit
 // MARK: - Edits
 
 extension TextLayoutManager: NSTextStorageDelegate {
-    /// Notifies the layout manager of an edit.
+    /// Receives edit notifications from the text storage and updates internal data structures to stay in sync with
+    /// text content.
     ///
-    /// Used by the `TextView` to tell the layout manager about any edits that will happen.
-    /// Use this to keep the layout manager's line storage in sync with the text storage.
+    /// If the changes are only attribute changes, this method invalidates layout for the edited range and returns.
     ///
-    /// - Parameters:
-    ///   - range: The range of the edit.
-    ///   - string: The string to replace in the given range.
-    public func willReplaceCharactersInRange(range: NSRange, with string: String) {
+    /// Otherwise, any lines that were removed or replaced by the edit are first removed from the text line layout
+    /// storage. Then, any new lines are inserted into the same storage.
+    ///
+    /// For instance, if inserting a newline this method will:
+    /// - Remove no lines (none were replaced)
+    /// - Update the current line's range to contain the newline character.
+    /// - Insert a new line after the current line.
+    ///
+    /// If a selection containing a newline is deleted and replaced with two more newlines this method will:
+    /// - Delete the original line.
+    /// - Insert two lines.
+    ///
+    /// - Note: This method *does not* cause a layout calculation. If a method is finding `NaN` values for line
+    ///         fragments, ensure `layout` or `ensureLayoutUntil` are called on the subject ranges.
+    public func textStorage(
+        _ textStorage: NSTextStorage,
+        didProcessEditing editedMask: NSTextStorageEditActions,
+        range editedRange: NSRange,
+        changeInLength delta: Int
+    ) {
+        guard editedMask.contains(.editedCharacters) else {
+            if editedMask.contains(.editedAttributes) && delta == 0 {
+                invalidateLayoutForRange(editedRange)
+            }
+            return
+        }
+
+        let insertedStringRange = NSRange(location: editedRange.location, length: editedRange.length - delta)
+        removeLayoutLinesIn(range: insertedStringRange)
+        insertNewLines(for: editedRange)
+        invalidateLayoutForRange(editedRange)
+    }
+
+    /// Removes all lines in the range, as if they were deleted. This is a setup for inserting the lines back in on an
+    /// edit.
+    /// - Parameter range: The range that was deleted.
+    private func removeLayoutLinesIn(range: NSRange) {
         // Loop through each line being replaced in reverse, updating and removing where necessary.
-         for linePosition in lineStorage.linesInRange(range).reversed() {
+        for linePosition in lineStorage.linesInRange(range).reversed() {
             // Two cases: Updated line, deleted line entirely
             guard let intersection = linePosition.range.intersection(range), !intersection.isEmpty else { continue }
             if intersection == linePosition.range && linePosition.range.max != lineStorage.length {
@@ -38,25 +71,24 @@ extension TextLayoutManager: NSTextStorageDelegate {
                 lineStorage.update(atIndex: linePosition.range.location, delta: -intersection.length, deltaHeight: 0)
             }
         }
-
+    }
+    
+    /// Inserts any newly inserted lines into the line layout storage. Exits early if the range is empty.
+    /// - Parameter range: The range of the string that was inserted into the text storage.
+    private func insertNewLines(for range: NSRange) {
+        guard !range.isEmpty, let string = textStorage?.substring(from: range) as? NSString else { return }
         // Loop through each line being inserted, inserting & splitting where necessary
-        if !string.isEmpty {
-            var index = 0
-            while let nextLine = (string as NSString).getNextLine(startingAt: index) {
-                let lineRange = NSRange(start: index, end: nextLine.max)
-                applyLineInsert((string as NSString).substring(with: lineRange) as NSString, at: range.location + index)
-                index = nextLine.max
-            }
+        var index = 0
+        while let nextLine = string.getNextLine(startingAt: index) {
+            let lineRange = NSRange(start: index, end: nextLine.max)
+            applyLineInsert(string.substring(with: lineRange) as NSString, at: range.location + index)
+            index = nextLine.max
+        }
 
-            if index < (string as NSString).length {
-                // Get the last line.
-                applyLineInsert(
-                    (string as NSString).substring(from: index) as NSString,
-                    at: range.location + index
-                )
-            }
+        if index < string.length {
+            // Get the last line.
+            applyLineInsert(string.substring(from: index) as NSString, at: range.location + index)
         }
-        setNeedsLayout()
     }
 
     /// Applies a line insert to the internal line storage tree.
@@ -96,18 +128,4 @@ extension TextLayoutManager: NSTextStorageDelegate {
             lineStorage.update(atIndex: location, delta: insertedString.length, deltaHeight: 0.0)
         }
     }
-
-    /// This method is to simplify keeping the layout manager in sync with attribute changes in the storage object.
-    /// This does not handle cases where characters have been inserted or removed from the storage.
-    /// For that, see the `willPerformEdit` method.
-    public func textStorage(
-        _ textStorage: NSTextStorage,
-        didProcessEditing editedMask: NSTextStorageEditActions,
-        range editedRange: NSRange,
-        changeInLength delta: Int
-    ) {
-        if editedMask.contains(.editedAttributes) && delta == 0 {
-            invalidateLayoutForRange(editedRange)
-        }
-    }
 }
diff --git a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Public.swift b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Public.swift
index f53e14f85..07cbcb00e 100644
--- a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Public.swift
+++ b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Public.swift
@@ -121,7 +121,7 @@ extension TextLayoutManager {
             return nil
         }
         if linePosition.data.lineFragments.isEmpty {
-            let newHeight = ensureLayoutFor(position: linePosition)
+            let newHeight = preparePositionForDisplay(linePosition)
             if linePosition.height != newHeight {
                 delegate?.layoutManagerHeightDidUpdate(newHeight: lineStorage.height)
             }
@@ -165,7 +165,8 @@ extension TextLayoutManager {
     ///   - line: The line to calculate rects for.
     /// - Returns: Multiple bounding rects. Will return one rect for each line fragment that overlaps the given range.
     public func rectsFor(range: NSRange) -> [CGRect] {
-        lineStorage.linesInRange(range).flatMap { self.rectsFor(range: range, in: $0) }
+        ensureLayoutUntil(range.max)
+        return lineStorage.linesInRange(range).flatMap { self.rectsFor(range: range, in: $0) }
     }
 
     /// Calculates all text bounding rects that intersect with a given range, with a given line position.
@@ -176,6 +177,8 @@ extension TextLayoutManager {
     private func rectsFor(range: NSRange, in line: borrowing TextLineStorage<TextLine>.TextLinePosition) -> [CGRect] {
         guard let textStorage = (textStorage?.string as? NSString) else { return [] }
 
+        _ = preparePositionForDisplay(line)
+
         // Don't make rects in between characters
         let realRangeStart = textStorage.rangeOfComposedCharacterSequence(at: range.lowerBound)
         let realRangeEnd = textStorage.rangeOfComposedCharacterSequence(at: range.upperBound - 1)
@@ -239,6 +242,8 @@ extension TextLayoutManager {
         // Combine the points in clockwise order
         let points = leftSidePoints + rightSidePoints
 
+        guard points.allSatisfy({ $0.x.isFinite && $0.y.isFinite }) else { return nil }
+
         // Close the path
         if let firstPoint = points.first {
             return NSBezierPath.smoothPath(points + [firstPoint], radius: cornerRadius)
@@ -286,7 +291,7 @@ extension TextLayoutManager {
         for linePosition in lineStorage.linesInRange(
             NSRange(start: startingLinePosition.range.location, end: linePosition.range.max)
         ) {
-            let height = ensureLayoutFor(position: linePosition)
+            let height = preparePositionForDisplay(linePosition)
             if height != linePosition.height {
                 lineStorage.update(
                     atIndex: linePosition.range.location,
diff --git a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Transaction.swift b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Transaction.swift
deleted file mode 100644
index c160bfd57..000000000
--- a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Transaction.swift
+++ /dev/null
@@ -1,38 +0,0 @@
-//
-//  TextLayoutManager+Transaction.swift
-//  CodeEditTextView
-//
-//  Created by Khan Winter on 2/24/24.
-//
-
-import Foundation
-
-extension TextLayoutManager {
-    /// Begins a transaction, preventing the layout manager from performing layout until the `endTransaction` is called.
-    /// Useful for grouping attribute modifications into one layout pass rather than laying out every update.
-    ///
-    /// You can nest transaction start/end calls, the layout manager will not cause layout until the last transaction
-    /// group is ended.
-    ///
-    /// Ensure there is a balanced number of begin/end calls. If there is a missing endTranscaction call, the layout
-    /// manager will never lay out text. If there is a end call without matching a start call an assertionFailure
-    /// will occur.
-    public func beginTransaction() {
-        transactionCounter += 1
-    }
-
-    /// Ends a transaction. When called, the layout manager will layout any necessary lines.
-    public func endTransaction(forceLayout: Bool = false) {
-        transactionCounter -= 1
-        if transactionCounter == 0 {
-            if forceLayout {
-                setNeedsLayout()
-            }
-            layoutLines()
-        } else if transactionCounter < 0 {
-            assertionFailure(
-                "TextLayoutManager.endTransaction called without a matching TextLayoutManager.beginTransaction call"
-            )
-        }
-    }
-}
diff --git a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+ensureLayout.swift b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+ensureLayout.swift
index e0e5fa07d..e2cf08d15 100644
--- a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+ensureLayout.swift
+++ b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+ensureLayout.swift
@@ -8,9 +8,10 @@
 import Foundation
 
 extension TextLayoutManager {
-    /// Forces layout calculation for all lines up to and including the given offset.
-    /// - Parameter offset: The offset to ensure layout until.
-    package func ensureLayoutFor(position: TextLineStorage<TextLine>.TextLinePosition) -> CGFloat {
+    /// Invalidates and prepares a line position for display.
+    /// - Parameter position: The line position to prepare.
+    /// - Returns: The height of the newly laid out line and all it's fragments.
+    package func preparePositionForDisplay(_ position: TextLineStorage<TextLine>.TextLinePosition) -> CGFloat {
         guard let textStorage else { return 0 }
         let displayData = TextLine.DisplayData(
             maxWidth: maxLineLayoutWidth,
diff --git a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager.swift b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager.swift
index 3e042225c..bf8782df9 100644
--- a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager.swift
+++ b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager.swift
@@ -211,15 +211,15 @@ public class TextLayoutManager: NSObject {
 
     /// Lays out all visible lines
     func layoutLines(in rect: NSRect? = nil) { // swiftlint:disable:this function_body_length
-        assertNotInLayout()
+//        assertNotInLayout()
         guard let visibleRect = rect ?? delegate?.visibleRect,
               !isInTransaction,
               let textStorage else {
             return
         }
-        #if DEBUG
-        isInLayout = true
-        #endif
+//        #if DEBUG
+//        isInLayout = true
+//        #endif
         let minY = max(visibleRect.minY - verticalLayoutPadding, 0)
         let maxY = max(visibleRect.maxY + verticalLayoutPadding, 0)
         let originalHeight = lineStorage.height
@@ -271,9 +271,9 @@ public class TextLayoutManager: NSObject {
         // Update the visible lines with the new set.
         visibleLineIds = newVisibleLines
 
-        #if DEBUG
-        isInLayout = false
-        #endif
+//        #if DEBUG
+//        isInLayout = false
+//        #endif
 
         // These are fine to update outside of `isInLayout` as our internal data structures are finalized at this point
         // so laying out again won't break our line storage or visible line.
diff --git a/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager+Update.swift b/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager+Update.swift
index 8ea0c7490..384aaba4b 100644
--- a/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager+Update.swift
+++ b/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager+Update.swift
@@ -6,22 +6,24 @@
 //
 
 import Foundation
+import AppKit
+
+extension TextSelectionManager: NSTextStorageDelegate {
+    public func textStorage(
+        _ textStorage: NSTextStorage,
+        didProcessEditing editedMask: NSTextStorageEditActions,
+        range editedRange: NSRange,
+        changeInLength delta: Int
+    ) {
+        guard editedMask.contains(.editedCharacters) else { return }
 
-extension TextSelectionManager {
-    public func didReplaceCharacters(in range: NSRange, replacementLength: Int) {
-        let delta = replacementLength == 0 ? -range.length : replacementLength
         for textSelection in self.textSelections {
-            if textSelection.range.location > range.max {
-                textSelection.range.location = max(0, textSelection.range.location + delta)
+            // If the text selection is ahead of the edited range, move it back by the range's length
+            if textSelection.range.location > editedRange.max {
+                textSelection.range.location += delta
                 textSelection.range.length = 0
-            } else if textSelection.range.intersection(range) != nil
-                        || textSelection.range == range
-                        || (textSelection.range.isEmpty && textSelection.range.location == range.max) {
-                if replacementLength > 0 {
-                    textSelection.range.location = range.location + replacementLength
-                } else {
-                    textSelection.range.location = range.location
-                }
+            } else if textSelection.range.intersection(editedRange) != nil {
+                textSelection.range.location = editedRange.max
                 textSelection.range.length = 0
             } else {
                 textSelection.range.length = 0
@@ -37,6 +39,8 @@ extension TextSelectionManager {
                 allRanges.insert(selection.range)
             }
         }
+
+        notifyAfterEdit()
     }
 
     func notifyAfterEdit() {
diff --git a/Sources/CodeEditTextView/TextView/TextView+ReplaceCharacters.swift b/Sources/CodeEditTextView/TextView/TextView+ReplaceCharacters.swift
index 06949b21a..b18c80f7a 100644
--- a/Sources/CodeEditTextView/TextView/TextView+ReplaceCharacters.swift
+++ b/Sources/CodeEditTextView/TextView/TextView+ReplaceCharacters.swift
@@ -16,7 +16,6 @@ extension TextView {
     public func replaceCharacters(in ranges: [NSRange], with string: String) {
         guard isEditable else { return }
         NotificationCenter.default.post(name: Self.textWillChangeNotification, object: self)
-        layoutManager.beginTransaction()
         textStorage.beginEditing()
 
         // Can't insert an empty string into an empty range. One must be not empty
@@ -25,7 +24,6 @@ extension TextView {
         (delegate?.textView(self, shouldReplaceContentsIn: range, with: string) ?? true) {
             delegate?.textView(self, willReplaceContentsIn: range, with: string)
 
-            layoutManager.willReplaceCharactersInRange(range: range, with: string)
             _undoManager?.registerMutation(
                 TextMutation(string: string as String, range: range, limit: textStorage.length)
             )
@@ -33,13 +31,11 @@ extension TextView {
                 in: range,
                 with: NSAttributedString(string: string, attributes: typingAttributes)
             )
-            selectionManager.didReplaceCharacters(in: range, replacementLength: (string as NSString).length)
 
             delegate?.textView(self, didReplaceContentsIn: range, with: string)
         }
 
         textStorage.endEditing()
-        layoutManager.endTransaction()
         selectionManager.notifyAfterEdit()
         NotificationCenter.default.post(name: Self.textDidChangeNotification, object: self)
 
diff --git a/Sources/CodeEditTextView/TextView/TextView.swift b/Sources/CodeEditTextView/TextView/TextView.swift
index 85b2e11b0..73e08b52a 100644
--- a/Sources/CodeEditTextView/TextView/TextView.swift
+++ b/Sources/CodeEditTextView/TextView/TextView.swift
@@ -58,7 +58,6 @@ public class TextView: NSView, NSTextContent {
             textStorage.string
         }
         set {
-            layoutManager.willReplaceCharactersInRange(range: documentRange, with: newValue)
             textStorage.setAttributedString(NSAttributedString(string: newValue, attributes: typingAttributes))
         }
     }
@@ -339,8 +338,10 @@ public class TextView: NSView, NSTextContent {
 
         layoutManager = setUpLayoutManager(lineHeightMultiplier: lineHeightMultiplier, wrapLines: wrapLines)
         storageDelegate.addDelegate(layoutManager)
+
         selectionManager = setUpSelectionManager()
         selectionManager.useSystemCursor = useSystemCursor
+        storageDelegate.addDelegate(selectionManager)
 
         _undoManager = CEUndoManager(textView: self)
 
diff --git a/Sources/CodeEditTextView/Utils/CEUndoManager.swift b/Sources/CodeEditTextView/Utils/CEUndoManager.swift
index c716d49b4..0aaaf842f 100644
--- a/Sources/CodeEditTextView/Utils/CEUndoManager.swift
+++ b/Sources/CodeEditTextView/Utils/CEUndoManager.swift
@@ -173,19 +173,13 @@ public class CEUndoManager {
 
     /// Groups all incoming mutations.
     public func beginUndoGrouping() {
-        guard !isGrouping else {
-            assertionFailure("UndoManager already in a group. Call `beginUndoGrouping` before this can be called.")
-            return
-        }
+        guard !isGrouping else { return }
         isGrouping = true
     }
 
     /// Stops grouping all incoming mutations.
     public func endUndoGrouping() {
-        guard isGrouping else {
-            assertionFailure("UndoManager not in a group. Call `endUndoGrouping` before this can be called.")
-            return
-        }
+        guard isGrouping else { return }
         isGrouping = false
     }
 

From c7ecbde1a071a6d778121a1d78ac8c28cec66e92 Mon Sep 17 00:00:00 2001
From: Khan Winter <35942988+thecoolwinter@users.noreply.github.com>
Date: Wed, 9 Apr 2025 09:59:04 -0500
Subject: [PATCH 2/8] Add `TextLayoutManager` Tests

---
 .../TextLayoutManager+Edits.swift             |   4 +-
 .../TextLayoutManagerTests.swift              | 102 ++++++++++++++++++
 2 files changed, 104 insertions(+), 2 deletions(-)
 create mode 100644 Tests/CodeEditTextViewTests/TextLayoutManagerTests.swift

diff --git a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Edits.swift b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Edits.swift
index 968e7389d..1c3d97240 100644
--- a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Edits.swift
+++ b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Edits.swift
@@ -72,7 +72,7 @@ extension TextLayoutManager: NSTextStorageDelegate {
             }
         }
     }
-    
+
     /// Inserts any newly inserted lines into the line layout storage. Exits early if the range is empty.
     /// - Parameter range: The range of the string that was inserted into the text storage.
     private func insertNewLines(for range: NSRange) {
@@ -97,7 +97,7 @@ extension TextLayoutManager: NSTextStorageDelegate {
     ///   - location: The location the string is being inserted into.
     private func applyLineInsert(_ insertedString: NSString, at location: Int) {
         if LineEnding(line: insertedString as String) != nil {
-            if location == textStorage?.length ?? 0 {
+            if location == lineStorage.length {
                 // Insert a new line at the end of the document, need to insert a new line 'cause there's nothing to
                 // split. Also, append the new text to the last line.
                 lineStorage.update(atIndex: location, delta: insertedString.length, deltaHeight: 0.0)
diff --git a/Tests/CodeEditTextViewTests/TextLayoutManagerTests.swift b/Tests/CodeEditTextViewTests/TextLayoutManagerTests.swift
new file mode 100644
index 000000000..164869250
--- /dev/null
+++ b/Tests/CodeEditTextViewTests/TextLayoutManagerTests.swift
@@ -0,0 +1,102 @@
+import Testing
+import AppKit
+@testable import CodeEditTextView
+
+extension TextLineStorage {
+    /// Validate that the internal tree is intact and correct.
+    ///
+    /// Ensures that:
+    /// - All lines can be queried by their index starting from `0`.
+    /// - All lines can be found by iterating `y` positions.
+    func validateInternalState() {
+        func validateLines(_ lines: [TextLineStorage<Data>.TextLinePosition]) {
+            var _lastLine: TextLineStorage<Data>.TextLinePosition?
+            for line in lines {
+                guard let lastLine = _lastLine else {
+                    #expect(line.index == 0)
+                    _lastLine = line
+                    return
+                }
+
+                #expect(line.index == lastLine.index + 1)
+                #expect(line.yPos >= lastLine.yPos + lastLine.height)
+                #expect(line.range.location == lastLine.range.max + 1)
+                _lastLine = line
+            }
+        }
+
+        let linesUsingIndex = (0..<count).compactMap({ getLine(atIndex: $0) })
+        validateLines(linesUsingIndex)
+
+        let linesUsingYValue = Array(linesStartingAt(0, until: height))
+        validateLines(linesUsingYValue)
+    }
+}
+
+@Suite
+@MainActor
+struct TextLayoutManagerTests {
+    let textView: TextView
+    let textStorage: NSTextStorage
+    let layoutManager: TextLayoutManager
+
+    init() throws {
+        textView = TextView(string: "A\nB\nC\nD")
+        textStorage = textView.textStorage
+        layoutManager = try #require(textView.layoutManager)
+    }
+
+    @Test(
+        arguments: [
+            ("\nE", NSRange(location: 6, length: 0), 5),
+            ("0\n", NSRange(location: 0, length: 0), 5), // at beginning
+            ("A\nBC\nD", NSRange(location: 3, length: 0), 6), // in middle
+            ("A\r\nB\nC\rD", NSRange(location: 0, length: 0), 7) // Insert mixed line breaks
+        ]
+    )
+    func insertText(_ testItem: (String, NSRange, Int)) throws { // swiftlint:disable:this large_tuple
+        let (insertText, insertRange, lineCount) = testItem
+
+        textStorage.replaceCharacters(in: insertRange, with: insertText)
+
+        #expect(layoutManager.lineCount == lineCount)
+        #expect(layoutManager.lineStorage.length == textStorage.length)
+        layoutManager.lineStorage.validateInternalState()
+    }
+
+    @Test(
+        arguments: [
+            (NSRange(location: 5, length: 2), 3), // At end
+            (NSRange(location: 0, length: 2), 3), // At beginning
+            (NSRange(location: 2, length: 3), 3) // In middle
+        ]
+    )
+    func deleteText(_ testItem: (NSRange, Int)) throws {
+        let (deleteRange, lineCount) = testItem
+
+        textStorage.deleteCharacters(in: deleteRange)
+
+        #expect(layoutManager.lineCount == lineCount)
+        #expect(layoutManager.lineStorage.length == textStorage.length)
+        layoutManager.lineStorage.validateInternalState()
+    }
+
+    @Test(
+        arguments: [
+            ("\nD\nE\nF", NSRange(location: 5, length: 2), 6), // At end
+            ("A\nY\nZ", NSRange(location: 0, length: 1), 6), // At beginning
+            ("1\n2\n", NSRange(location: 2, length: 4), 4), // In middle
+            ("A\nB\nC\nD\nE\nF\nG", NSRange(location: 0, length: 7), 7), // Entire string
+            ("A\r\nB\nC\r", NSRange(location: 0, length: 6), 4) // Mixed line breaks
+        ]
+    )
+    func replaceText(_ testItem: (String, NSRange, Int)) throws { // swiftlint:disable:this large_tuple
+        let (replaceText, replaceRange, lineCount) = testItem
+
+        textStorage.replaceCharacters(in: replaceRange, with: replaceText)
+
+        #expect(layoutManager.lineCount == lineCount)
+        #expect(layoutManager.lineStorage.length == textStorage.length)
+        layoutManager.lineStorage.validateInternalState()
+    }
+}

From d447d78bce823df64908e95f5a7b5c68c03cf968 Mon Sep 17 00:00:00 2001
From: Khan Winter <35942988+thecoolwinter@users.noreply.github.com>
Date: Wed, 9 Apr 2025 10:19:40 -0500
Subject: [PATCH 3/8] Fix `rectsFor(range:line:)` Removing Layout Info

---
 .../TextLayoutManager/TextLayoutManager+Public.swift            | 2 --
 1 file changed, 2 deletions(-)

diff --git a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Public.swift b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Public.swift
index 07cbcb00e..6ba0c0b5e 100644
--- a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Public.swift
+++ b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Public.swift
@@ -177,8 +177,6 @@ extension TextLayoutManager {
     private func rectsFor(range: NSRange, in line: borrowing TextLineStorage<TextLine>.TextLinePosition) -> [CGRect] {
         guard let textStorage = (textStorage?.string as? NSString) else { return [] }
 
-        _ = preparePositionForDisplay(line)
-
         // Don't make rects in between characters
         let realRangeStart = textStorage.rangeOfComposedCharacterSequence(at: range.lowerBound)
         let realRangeEnd = textStorage.rangeOfComposedCharacterSequence(at: range.upperBound - 1)

From c45d93e61ba2a681294ca619a00314fde0f73a2b Mon Sep 17 00:00:00 2001
From: Khan Winter <35942988+thecoolwinter@users.noreply.github.com>
Date: Wed, 9 Apr 2025 10:19:53 -0500
Subject: [PATCH 4/8] Revert SelectionManager Changes

---
 .../TextSelectionManager+Update.swift         | 30 +++++++++----------
 .../TextView/TextView+ReplaceCharacters.swift |  1 +
 .../CodeEditTextView/TextView/TextView.swift  |  1 -
 3 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager+Update.swift b/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager+Update.swift
index 384aaba4b..338e166cb 100644
--- a/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager+Update.swift
+++ b/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager+Update.swift
@@ -8,22 +8,22 @@
 import Foundation
 import AppKit
 
-extension TextSelectionManager: NSTextStorageDelegate {
-    public func textStorage(
-        _ textStorage: NSTextStorage,
-        didProcessEditing editedMask: NSTextStorageEditActions,
-        range editedRange: NSRange,
-        changeInLength delta: Int
-    ) {
-        guard editedMask.contains(.editedCharacters) else { return }
-
+extension TextSelectionManager {
+    public func didReplaceCharacters(in range: NSRange, replacementLength: Int) {
+        let delta = replacementLength == 0 ? -range.length : replacementLength
         for textSelection in self.textSelections {
-            // If the text selection is ahead of the edited range, move it back by the range's length
-            if textSelection.range.location > editedRange.max {
-                textSelection.range.location += delta
+            if textSelection.range.location > range.max {
+                textSelection.range.location = max(0, textSelection.range.location + delta)
+
                 textSelection.range.length = 0
-            } else if textSelection.range.intersection(editedRange) != nil {
-                textSelection.range.location = editedRange.max
+            } else if textSelection.range.intersection(range) != nil
+                        || textSelection.range == range
+                        || (textSelection.range.isEmpty && textSelection.range.location == range.max) {
+                if replacementLength > 0 {
+                    textSelection.range.location = range.location + replacementLength
+                } else {
+                    textSelection.range.location = range.location
+                }
                 textSelection.range.length = 0
             } else {
                 textSelection.range.length = 0
@@ -39,8 +39,6 @@ extension TextSelectionManager: NSTextStorageDelegate {
                 allRanges.insert(selection.range)
             }
         }
-
-        notifyAfterEdit()
     }
 
     func notifyAfterEdit() {
diff --git a/Sources/CodeEditTextView/TextView/TextView+ReplaceCharacters.swift b/Sources/CodeEditTextView/TextView/TextView+ReplaceCharacters.swift
index b18c80f7a..951e9977e 100644
--- a/Sources/CodeEditTextView/TextView/TextView+ReplaceCharacters.swift
+++ b/Sources/CodeEditTextView/TextView/TextView+ReplaceCharacters.swift
@@ -31,6 +31,7 @@ extension TextView {
                 in: range,
                 with: NSAttributedString(string: string, attributes: typingAttributes)
             )
+            selectionManager.didReplaceCharacters(in: range, replacementLength: (string as NSString).length)
 
             delegate?.textView(self, didReplaceContentsIn: range, with: string)
         }
diff --git a/Sources/CodeEditTextView/TextView/TextView.swift b/Sources/CodeEditTextView/TextView/TextView.swift
index 73e08b52a..9b0337f9e 100644
--- a/Sources/CodeEditTextView/TextView/TextView.swift
+++ b/Sources/CodeEditTextView/TextView/TextView.swift
@@ -341,7 +341,6 @@ public class TextView: NSView, NSTextContent {
 
         selectionManager = setUpSelectionManager()
         selectionManager.useSystemCursor = useSystemCursor
-        storageDelegate.addDelegate(selectionManager)
 
         _undoManager = CEUndoManager(textView: self)
 

From 7b56c7c376547d4f257604c40b0307631201d335 Mon Sep 17 00:00:00 2001
From: Khan Winter <35942988+thecoolwinter@users.noreply.github.com>
Date: Wed, 9 Apr 2025 10:42:13 -0500
Subject: [PATCH 5/8] Add Invalidated Layout Test, Delegate Editing Test,
 Remove Layout Manager Assertion

---
 .../TextLayoutManager/TextLayoutManager.swift | 16 -------
 .../EmphasisManagerTests.swift                |  3 +-
 .../TextLayoutManagerTests.swift              | 31 +++++++++++++
 .../CodeEditTextViewTests/TextViewTests.swift | 43 +++++++++++++++++++
 4 files changed, 76 insertions(+), 17 deletions(-)
 create mode 100644 Tests/CodeEditTextViewTests/TextViewTests.swift

diff --git a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager.swift b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager.swift
index bf8782df9..b281c0ce3 100644
--- a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager.swift
+++ b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager.swift
@@ -201,25 +201,13 @@ public class TextLayoutManager: NSObject {
 
     // MARK: - Layout
 
-    /// Asserts that the caller is not in an active layout pass.
-    /// See docs on ``isInLayout`` for more details.
-    private func assertNotInLayout() {
-        #if DEBUG // This is redundant, but it keeps the flag debug-only too which helps prevent misuse.
-        assert(!isInLayout, "layoutLines called while already in a layout pass. This is a programmer error.")
-        #endif
-    }
-
     /// Lays out all visible lines
     func layoutLines(in rect: NSRect? = nil) { // swiftlint:disable:this function_body_length
-//        assertNotInLayout()
         guard let visibleRect = rect ?? delegate?.visibleRect,
               !isInTransaction,
               let textStorage else {
             return
         }
-//        #if DEBUG
-//        isInLayout = true
-//        #endif
         let minY = max(visibleRect.minY - verticalLayoutPadding, 0)
         let maxY = max(visibleRect.maxY + verticalLayoutPadding, 0)
         let originalHeight = lineStorage.height
@@ -271,10 +259,6 @@ public class TextLayoutManager: NSObject {
         // Update the visible lines with the new set.
         visibleLineIds = newVisibleLines
 
-//        #if DEBUG
-//        isInLayout = false
-//        #endif
-
         // These are fine to update outside of `isInLayout` as our internal data structures are finalized at this point
         // so laying out again won't break our line storage or visible line.
 
diff --git a/Tests/CodeEditTextViewTests/EmphasisManagerTests.swift b/Tests/CodeEditTextViewTests/EmphasisManagerTests.swift
index a921f1051..4cdf8468b 100644
--- a/Tests/CodeEditTextViewTests/EmphasisManagerTests.swift
+++ b/Tests/CodeEditTextViewTests/EmphasisManagerTests.swift
@@ -4,7 +4,8 @@ import Foundation
 
 @Suite()
 struct EmphasisManagerTests {
-    @Test() @MainActor
+    @Test()
+    @MainActor
     func testFlashEmphasisLayersNotLeaked() {
         // Ensure layers are not leaked when switching from flash emphasis to any other emphasis type.
         let textView = TextView(string: "Lorem Ipsum")
diff --git a/Tests/CodeEditTextViewTests/TextLayoutManagerTests.swift b/Tests/CodeEditTextViewTests/TextLayoutManagerTests.swift
index 164869250..6eb1d97c7 100644
--- a/Tests/CodeEditTextViewTests/TextLayoutManagerTests.swift
+++ b/Tests/CodeEditTextViewTests/TextLayoutManagerTests.swift
@@ -42,6 +42,7 @@ struct TextLayoutManagerTests {
 
     init() throws {
         textView = TextView(string: "A\nB\nC\nD")
+        textView.frame = NSRect(x: 0, y: 0, width: 1000, height: 1000)
         textStorage = textView.textStorage
         layoutManager = try #require(textView.layoutManager)
     }
@@ -99,4 +100,34 @@ struct TextLayoutManagerTests {
         #expect(layoutManager.lineStorage.length == textStorage.length)
         layoutManager.lineStorage.validateInternalState()
     }
+
+    /// # 04/09/25
+    /// This ensures that getting line rect info does not invalidate layout. The issue was previously caused by a call to
+    /// ``TextLayoutManager/preparePositionForDisplay``.
+    @Test
+    func getRectsDoesNotRemoveLayoutInfo() {
+        layoutManager.layoutLines(in: NSRect(x: 0, y: 0, width: 1000, height: 1000))
+        let lineFragmentIDs = Set(
+            layoutManager.lineStorage
+                .linesInRange(NSRange(location: 0, length: 7))
+                .flatMap(\.data.lineFragments)
+                .map(\.data.id)
+        )
+
+        _ = layoutManager.rectsFor(range: NSRange(start: 0, end: 7))
+
+        #expect(
+            layoutManager.lineStorage.linesInRange(NSRange(location: 0, length: 7)).allSatisfy({ position in
+                !position.data.lineFragments.isEmpty
+            })
+        )
+        let afterLineFragmentIDs = Set(
+            layoutManager.lineStorage
+                .linesInRange(NSRange(location: 0, length: 7))
+                .flatMap(\.data.lineFragments)
+                .map(\.data.id)
+        )
+        #expect(lineFragmentIDs == afterLineFragmentIDs, "Line fragments were invalidated by `rectsFor(range:)` call.")
+        layoutManager.lineStorage.validateInternalState()
+    }
 }
diff --git a/Tests/CodeEditTextViewTests/TextViewTests.swift b/Tests/CodeEditTextViewTests/TextViewTests.swift
new file mode 100644
index 000000000..da5056d27
--- /dev/null
+++ b/Tests/CodeEditTextViewTests/TextViewTests.swift
@@ -0,0 +1,43 @@
+import Testing
+import AppKit
+@testable import CodeEditTextView
+
+@Suite
+@MainActor
+struct TextViewTests {
+    class MockDelegate: TextViewDelegate {
+        var shouldReplaceContents: ((_ textView: TextView, _ range: NSRange, _ string: String) -> Bool)?
+
+        func textView(_ textView: TextView, shouldReplaceContentsIn range: NSRange, with string: String) -> Bool {
+            shouldReplaceContents?(textView, range, string) ?? true
+        }
+    }
+
+    let textView: TextView
+    let delegate: MockDelegate
+
+    init() {
+        textView = TextView(string: "Lorem Ipsum")
+        delegate = MockDelegate()
+        textView.delegate = delegate
+    }
+
+    @Test
+    func delegateChangesText() {
+        var hasReplaced = false
+        delegate.shouldReplaceContents = { textView, _, _ -> Bool in
+            if !hasReplaced {
+                hasReplaced.toggle()
+                textView.replaceCharacters(in: NSRange(location: 0, length: 0), with: " World ")
+            }
+
+            return true
+        }
+
+        textView.replaceCharacters(in: NSRange(location: 0, length: 0), with: "Hello")
+
+        #expect(textView.string == "Hello World Lorem Ipsum")
+        // available in test module
+        textView.layoutManager.lineStorage.validateInternalState()
+    }
+}

From 13a455ef64453e65c7fe0138963e5eec7188e5ca Mon Sep 17 00:00:00 2001
From: Khan Winter <35942988+thecoolwinter@users.noreply.github.com>
Date: Wed, 9 Apr 2025 10:44:57 -0500
Subject: [PATCH 6/8] Lint Error

---
 Tests/CodeEditTextViewTests/TextLayoutManagerTests.swift | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Tests/CodeEditTextViewTests/TextLayoutManagerTests.swift b/Tests/CodeEditTextViewTests/TextLayoutManagerTests.swift
index 6eb1d97c7..1dcc9a7dd 100644
--- a/Tests/CodeEditTextViewTests/TextLayoutManagerTests.swift
+++ b/Tests/CodeEditTextViewTests/TextLayoutManagerTests.swift
@@ -102,8 +102,8 @@ struct TextLayoutManagerTests {
     }
 
     /// # 04/09/25
-    /// This ensures that getting line rect info does not invalidate layout. The issue was previously caused by a call to
-    /// ``TextLayoutManager/preparePositionForDisplay``.
+    /// This ensures that getting line rect info does not invalidate layout. The issue was previously caused by a
+    /// call to ``TextLayoutManager/preparePositionForDisplay``.
     @Test
     func getRectsDoesNotRemoveLayoutInfo() {
         layoutManager.layoutLines(in: NSRect(x: 0, y: 0, width: 1000, height: 1000))

From 49aee7fb42c215231d6b348e937b817c0cc25e09 Mon Sep 17 00:00:00 2001
From: Khan Winter <35942988+thecoolwinter@users.noreply.github.com>
Date: Wed, 9 Apr 2025 10:51:43 -0500
Subject: [PATCH 7/8] Revert Final Changes in Selection Update

---
 .../TextSelectionManager/TextSelectionManager+Update.swift      | 2 --
 1 file changed, 2 deletions(-)

diff --git a/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager+Update.swift b/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager+Update.swift
index 338e166cb..8ea0c7490 100644
--- a/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager+Update.swift
+++ b/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager+Update.swift
@@ -6,7 +6,6 @@
 //
 
 import Foundation
-import AppKit
 
 extension TextSelectionManager {
     public func didReplaceCharacters(in range: NSRange, replacementLength: Int) {
@@ -14,7 +13,6 @@ extension TextSelectionManager {
         for textSelection in self.textSelections {
             if textSelection.range.location > range.max {
                 textSelection.range.location = max(0, textSelection.range.location + delta)
-
                 textSelection.range.length = 0
             } else if textSelection.range.intersection(range) != nil
                         || textSelection.range == range

From 21b7e346323436fec3c438c3c26136b2fcc0bd61 Mon Sep 17 00:00:00 2001
From: Khan Winter <35942988+thecoolwinter@users.noreply.github.com>
Date: Wed, 9 Apr 2025 11:27:45 -0500
Subject: [PATCH 8/8] Assert When Layout Is Recursively Called

---
 .../TextLayoutManager+Public.swift            |  1 +
 .../TextLayoutManager/TextLayoutManager.swift | 23 +++++++++++++++++++
 .../TextSelectionManager.swift                |  7 +++++-
 3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Public.swift b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Public.swift
index 6ba0c0b5e..6fa1d9c9e 100644
--- a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Public.swift
+++ b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Public.swift
@@ -191,6 +191,7 @@ extension TextLayoutManager {
         for fragmentPosition in line.data.lineFragments.linesInRange(relativeRange) {
             guard let intersectingRange = fragmentPosition.range.intersection(relativeRange) else { continue }
             let fragmentRect = fragmentPosition.data.rectFor(range: intersectingRange)
+            guard fragmentRect.width > 0 else { continue }
             rects.append(
                 CGRect(
                     x: fragmentRect.minX + edgeInsets.left,
diff --git a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager.swift b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager.swift
index b281c0ce3..880c28748 100644
--- a/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager.swift
+++ b/Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager.swift
@@ -199,15 +199,33 @@ public class TextLayoutManager: NSObject {
     /// ``TextLayoutManager/estimateLineHeight()`` is called.
     private var _estimateLineHeight: CGFloat?
 
+    /// Asserts that the caller is not in an active layout pass.
+    /// See docs on ``isInLayout`` for more details.
+    private func assertNotInLayout() {
+        #if DEBUG // This is redundant, but it keeps the flag debug-only too which helps prevent misuse.
+        assert(!isInLayout, "layoutLines called while already in a layout pass. This is a programmer error.")
+        #endif
+    }
+
     // MARK: - Layout
 
     /// Lays out all visible lines
     func layoutLines(in rect: NSRect? = nil) { // swiftlint:disable:this function_body_length
+        assertNotInLayout()
         guard let visibleRect = rect ?? delegate?.visibleRect,
               !isInTransaction,
               let textStorage else {
             return
         }
+
+        // The macOS may call `layout` on the textView while we're laying out fragment views. This ensures the view
+        // tree modifications caused by this method are atomic, so macOS won't call `layout` while we're already doing
+        // that
+        CATransaction.begin()
+        #if DEBUG
+        isInLayout = true
+        #endif
+
         let minY = max(visibleRect.minY - verticalLayoutPadding, 0)
         let maxY = max(visibleRect.maxY + verticalLayoutPadding, 0)
         let originalHeight = lineStorage.height
@@ -253,6 +271,11 @@ public class TextLayoutManager: NSObject {
             newVisibleLines.insert(linePosition.data.id)
         }
 
+        #if DEBUG
+        isInLayout = false
+        #endif
+        CATransaction.commit()
+
         // Enqueue any lines not used in this layout pass.
         viewReuseQueue.enqueueViews(notInSet: usedFragmentIDs)
 
diff --git a/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager.swift b/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager.swift
index 453fcac87..a56c73a68 100644
--- a/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager.swift
+++ b/Sources/CodeEditTextView/TextSelectionManager/TextSelectionManager.swift
@@ -86,6 +86,8 @@ public class TextSelectionManager: NSObject {
     /// Set the selected ranges to new ranges. Overrides any existing selections.
     /// - Parameter range: The selected ranges to set.
     public func setSelectedRanges(_ ranges: [NSRange]) {
+        let oldRanges = textSelections.map(\.range)
+
         textSelections.forEach { $0.view?.removeFromSuperview() }
         // Remove duplicates, invalid ranges, update suggested X position.
         textSelections = Set(ranges)
@@ -99,8 +101,11 @@ public class TextSelectionManager: NSObject {
                 return selection
             }
         updateSelectionViews()
-        NotificationCenter.default.post(Notification(name: Self.selectionChangedNotification, object: self))
         delegate?.setNeedsDisplay()
+
+        if oldRanges != textSelections.map(\.range) {
+            NotificationCenter.default.post(Notification(name: Self.selectionChangedNotification, object: self))
+        }
     }
 
     /// Append a new selected range to the existing ones.