From f2f9d9307572789bdef0259c0606bf3e8c8c5830 Mon Sep 17 00:00:00 2001
From: Khan Winter <35942988+thecoolwinter@users.noreply.github.com>
Date: Thu, 15 Feb 2024 13:30:35 -0600
Subject: [PATCH] Fix CRLF Line Ending Typesetting (#20)

---
 .../TextLine/Typesetter.swift                 | 29 +++++++-
 .../TypesetterTests.swift                     | 74 +++++++++++++++++++
 2 files changed, 100 insertions(+), 3 deletions(-)
 create mode 100644 Tests/CodeEditTextViewTests/TypesetterTests.swift

diff --git a/Sources/CodeEditTextView/TextLine/Typesetter.swift b/Sources/CodeEditTextView/TextLine/Typesetter.swift
index 63961ce6..9628bde2 100644
--- a/Sources/CodeEditTextView/TextLine/Typesetter.swift
+++ b/Sources/CodeEditTextView/TextLine/Typesetter.swift
@@ -182,8 +182,18 @@ final class Typesetter {
         startingOffset: Int,
         constrainingWidth: CGFloat
     ) -> Int {
-        let breakIndex = startingOffset + CTTypesetterSuggestClusterBreak(typesetter, startingOffset, constrainingWidth)
-        if breakIndex >= string.length || (breakIndex - 1 > 0 && ensureCharacterCanBreakLine(at: breakIndex - 1)) {
+        var breakIndex = startingOffset + CTTypesetterSuggestClusterBreak(typesetter, startingOffset, constrainingWidth)
+
+        let isBreakAtEndOfString = breakIndex >= string.length
+
+        let isNextCharacterCarriageReturn = checkIfLineBreakOnCRLF(breakIndex)
+        if isNextCharacterCarriageReturn {
+            breakIndex += 1
+        }
+
+        let canLastCharacterBreak = (breakIndex - 1 > 0 && ensureCharacterCanBreakLine(at: breakIndex - 1))
+
+        if isBreakAtEndOfString || canLastCharacterBreak {
             // Breaking either at the end of the string, or on a whitespace.
             return breakIndex
         } else if breakIndex - 1 > 0 {
@@ -208,7 +218,20 @@ final class Typesetter {
         let set = CharacterSet(
             charactersIn: string.attributedSubstring(from: NSRange(location: index, length: 1)).string
         )
-        return set.isSubset(of: .whitespaces) || set.isSubset(of: .punctuationCharacters)
+        return set.isSubset(of: .whitespacesAndNewlines) || set.isSubset(of: .punctuationCharacters)
+    }
+
+    /// Check if the break index is on a CRLF (`\r\n`) character, indicating a valid break position.
+    /// - Parameter breakIndex: The index to check in the string.
+    /// - Returns: True, if the break index lies after the `\n` character in a `\r\n` sequence.
+    private func checkIfLineBreakOnCRLF(_ breakIndex: Int) -> Bool {
+        guard breakIndex - 1 > 0 && breakIndex + 1 <= string.length else {
+            return false
+        }
+        let substringRange = NSRange(location: breakIndex - 1, length: 2)
+        let substring = string.attributedSubstring(from: substringRange).string
+
+        return substring == LineEnding.carriageReturnLineFeed.rawValue
     }
 
     deinit {
diff --git a/Tests/CodeEditTextViewTests/TypesetterTests.swift b/Tests/CodeEditTextViewTests/TypesetterTests.swift
new file mode 100644
index 00000000..07954a7c
--- /dev/null
+++ b/Tests/CodeEditTextViewTests/TypesetterTests.swift
@@ -0,0 +1,74 @@
+import XCTest
+@testable import CodeEditTextView
+
+// swiftlint:disable all
+
+class TypesetterTests: XCTestCase {
+    let limitedLineWidthDisplayData = TextLine.DisplayData(maxWidth: 150, lineHeightMultiplier: 1.0, estimatedLineHeight: 20.0)
+    let unlimitedLineWidthDisplayData = TextLine.DisplayData(maxWidth: .infinity, lineHeightMultiplier: 1.0, estimatedLineHeight: 20.0)
+
+    func test_LineFeedBreak() {
+        let typesetter = Typesetter()
+        typesetter.typeset(
+            NSAttributedString(string: "testline\n"),
+            displayData: unlimitedLineWidthDisplayData,
+            breakStrategy: .word,
+            markedRanges: nil
+        )
+
+        XCTAssertEqual(typesetter.lineFragments.count, 1, "Typesetter typeset incorrect number of lines.")
+
+        typesetter.typeset(
+            NSAttributedString(string: "testline\n"),
+            displayData: unlimitedLineWidthDisplayData,
+            breakStrategy: .character,
+            markedRanges: nil
+        )
+
+        XCTAssertEqual(typesetter.lineFragments.count, 1, "Typesetter typeset incorrect number of lines.")
+    }
+
+    func test_carriageReturnBreak() {
+        let typesetter = Typesetter()
+        typesetter.typeset(
+            NSAttributedString(string: "testline\r"),
+            displayData: unlimitedLineWidthDisplayData,
+            breakStrategy: .word,
+            markedRanges: nil
+        )
+
+        XCTAssertEqual(typesetter.lineFragments.count, 1, "Typesetter typeset incorrect number of lines.")
+
+        typesetter.typeset(
+            NSAttributedString(string: "testline\r"),
+            displayData: unlimitedLineWidthDisplayData,
+            breakStrategy: .character,
+            markedRanges: nil
+        )
+
+        XCTAssertEqual(typesetter.lineFragments.count, 1, "Typesetter typeset incorrect number of lines.")
+    }
+
+    func test_carriageReturnLineFeedBreak() {
+        let typesetter = Typesetter()
+        typesetter.typeset(
+            NSAttributedString(string: "testline\r\n"),
+            displayData: unlimitedLineWidthDisplayData,
+            breakStrategy: .word,
+            markedRanges: nil
+        )
+
+        XCTAssertEqual(typesetter.lineFragments.count, 1, "Typesetter typeset incorrect number of lines.")
+
+        typesetter.typeset(
+            NSAttributedString(string: "testline\r\n"),
+            displayData: unlimitedLineWidthDisplayData,
+            breakStrategy: .character,
+            markedRanges: nil
+        )
+
+        XCTAssertEqual(typesetter.lineFragments.count, 1, "Typesetter typeset incorrect number of lines.")
+    }
+}
+
+// swiftlint:enable all