Add AppKit NSTextDiffView API and unify SwiftUI rendering

Package.swift

@@ -24,7 +24,11 @@ let package = Package(
         // Targets are the basic building blocks of a package, defining a module or a test suite.
         // Targets can depend on other targets in this package and products from dependencies.
         .target(
-            name: "TextDiff"),
+            name: "TextDiff",
+            swiftSettings: [
+                .define("TESTING", .when(configuration: .debug))
+            ]
+        ),
         .testTarget(
             name: "TextDiffTests",
             dependencies: [

README.md

@@ -1,6 +1,6 @@
 # TextDiff
 
-TextDiff is a macOS Swift package that computes token-level diffs and renders a merged, display-only SwiftUI view backed by a custom AppKit renderer.
+TextDiff is a macOS Swift package that computes token-level diffs and renders a merged, display-only diff view for both SwiftUI (`TextDiffView`) and AppKit (`NSTextDiffView`) via the same custom AppKit renderer.
 
 ![TextDiff preview](Resources/textdiff-preview.png)
 
@@ -43,6 +43,30 @@ struct DemoView: View {
 }
 ```
 
+## AppKit Usage
+
+```swift
+import AppKit
+import TextDiff
+
+let diffView = NSTextDiffView(
+    original: "This is teh old sentence.",
+    updated: "This is the updated sentence!",
+    mode: .token
+)
+
+// Constrain width in your layout. Height is intrinsic and computed from width.
+diffView.translatesAutoresizingMaskIntoConstraints = false
+```
+
+You can update content in place:
+
+```swift
+diffView.mode = .character
+diffView.original = "Add a diff"
+diffView.updated = "Added a diff"
+```
+
 ## Comparison Modes
 
 ```swift
@@ -101,14 +125,15 @@ struct StyledDemoView: View {
 - No synthetic spacer characters are inserted into the rendered text stream.
 - Chip top/bottom clipping is prevented internally via explicit line-height and vertical content insets.
 - Moved text is not detected as a move; it appears as delete + insert.
-- Rendering uses a custom AppKit draw view bridged into SwiftUI.
+- Rendering uses a custom AppKit draw view shared by both `TextDiffView` and `NSTextDiffView`.
 
 ## Snapshot Testing
 
 Snapshot coverage uses [Point-Free SnapshotTesting](https://github.com/pointfreeco/swift-snapshot-testing) with `swift-testing`.
 
 - Snapshot tests live in `Tests/TextDiffTests/TextDiffSnapshotTests.swift`.
-- Baselines are stored under `Tests/TextDiffTests/__Snapshots__/TextDiffSnapshotTests/`.
+- AppKit snapshot tests live in `Tests/TextDiffTests/NSTextDiffSnapshotTests.swift`.
+- Baselines are stored under `Tests/TextDiffTests/__Snapshots__/TextDiffSnapshotTests/` and `Tests/TextDiffTests/__Snapshots__/NSTextDiffSnapshotTests/`.
 - The suite uses `@Suite(.snapshots(record: .missing))` to record only missing baselines.
 
 Run all tests:
@@ -119,7 +144,7 @@ swift test 2>&1 | xcsift --quiet
 
 Update baselines intentionally:
 
-1. Temporarily switch the suite trait in `Tests/TextDiffTests/TextDiffSnapshotTests.swift` from `.missing` to `.all`.
+1. Temporarily switch the suite trait in snapshot suites (for example, `Tests/TextDiffTests/TextDiffSnapshotTests.swift` and `Tests/TextDiffTests/NSTextDiffSnapshotTests.swift`) from `.missing` to `.all`.
 2. Run `swift test 2>&1 | xcsift --quiet` once to rewrite baselines.
 3. Switch the suite trait back to `.missing`.
 4. Review snapshot image diffs in your PR before merging.

Sources/TextDiff/AppKit/DiffTextLayoutMetrics.swift

@@ -0,0 +1,13 @@
+import AppKit
+
+enum DiffTextLayoutMetrics {
+    static func verticalTextInset(for style: TextDiffStyle) -> CGFloat {
+        ceil(max(2, style.chipInsets.top + 2, style.chipInsets.bottom + 2))
+    }
+
+    static func lineHeight(for style: TextDiffStyle) -> CGFloat {
+        let textHeight = ceil(style.font.ascender - style.font.descender + style.font.leading)
+        let chipHeight = textHeight + style.chipInsets.top + style.chipInsets.bottom
+        return ceil(chipHeight + max(0, style.lineSpacing))
+    }
+}

Sources/TextDiff/AppKit/DiffTextViewRepresentable.swift

@@ -1,31 +1,30 @@
 import AppKit
 import SwiftUI
 
-enum DiffTextLayoutMetrics {
-    static func verticalTextInset(for style: TextDiffStyle) -> CGFloat {
-        ceil(max(2, style.chipInsets.top + 2, style.chipInsets.bottom + 2))
-    }
-
-    static func lineHeight(for style: TextDiffStyle) -> CGFloat {
-        let textHeight = ceil(style.font.ascender - style.font.descender + style.font.leading)
-        let chipHeight = textHeight + style.chipInsets.top + style.chipInsets.bottom
-        return ceil(chipHeight + max(0, style.lineSpacing))
-    }
-}
-
 struct DiffTextViewRepresentable: NSViewRepresentable {
-    let segments: [DiffSegment]
+    let original: String
+    let updated: String
     let style: TextDiffStyle
+    let mode: TextDiffComparisonMode
 
-    func makeNSView(context: Context) -> DiffCanvasView {
-        let view = DiffCanvasView()
+    func makeNSView(context: Context) -> NSTextDiffView {
+        let view = NSTextDiffView(
+            original: original,
+            updated: updated,
+            style: style,
+            mode: mode
+        )
         view.setContentCompressionResistancePriority(.required, for: .vertical)
         view.setContentHuggingPriority(.required, for: .vertical)
-        view.update(segments: segments, style: style)
         return view
     }
 
-    func updateNSView(_ view: DiffCanvasView, context: Context) {
-        view.update(segments: segments, style: style)
+    func updateNSView(_ view: NSTextDiffView, context: Context) {
+        view.setContent(
+            original: original,
+            updated: updated,
+            style: style,
+            mode: mode
+        )
     }
 }