prevent recomputations

Author: iSapozhnik

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: [

Sources/TextDiff/AppKit/DiffTextViewRepresentable.swift

@@ -20,9 +20,11 @@ struct DiffTextViewRepresentable: NSViewRepresentable {
     }
 
     func updateNSView(_ view: NSTextDiffView, context: Context) {
-        view.style = style
-        view.mode = mode
-        view.original = original
-        view.updated = updated
+        view.setContent(
+            original: original,
+            updated: updated,
+            style: style,
+            mode: mode
+        )
     }
 }

Sources/TextDiff/AppKit/NSTextDiffView.swift

@@ -9,22 +9,32 @@ public final class NSTextDiffView: NSView {
     /// Setting this value updates rendered diff output when content changes.
     public var original: String {
         didSet {
-            updateSegmentsIfNeeded()
+            guard !isBatchUpdating else {
+                return
+            }
+            _ = updateSegmentsIfNeeded()
         }
     }
 
     /// The source text after edits.
     /// Setting this value updates rendered diff output when content changes.
     public var updated: String {
         didSet {
-            updateSegmentsIfNeeded()
+            guard !isBatchUpdating else {
+                return
+            }
+            _ = updateSegmentsIfNeeded()
         }
     }
 
     /// Visual style used to render additions, deletions, and unchanged text.
     /// Setting this value redraws the view without recomputing diff segments.
     public var style: TextDiffStyle {
         didSet {
+            guard !isBatchUpdating else {
+                pendingStyleInvalidation = true
+                return
+            }
             invalidateCachedLayout()
         }
     }
@@ -33,7 +43,10 @@ public final class NSTextDiffView: NSView {
     /// Setting this value updates rendered diff output when mode changes.
     public var mode: TextDiffComparisonMode {
         didSet {
-            updateSegmentsIfNeeded()
+            guard !isBatchUpdating else {
+                return
+            }
+            _ = updateSegmentsIfNeeded()
         }
     }
 
@@ -43,6 +56,8 @@ public final class NSTextDiffView: NSView {
     private var lastOriginal: String
     private var lastUpdated: String
     private var lastModeKey: Int
+    private var isBatchUpdating = false
+    private var pendingStyleInvalidation = false
 
     private var cachedWidth: CGFloat = -1
     private var cachedLayout: DiffLayout?
@@ -83,6 +98,7 @@ public final class NSTextDiffView: NSView {
         super.init(frame: .zero)
     }
 
+    #if TESTING
     init(
         original: String,
         updated: String,
@@ -101,6 +117,7 @@ public final class NSTextDiffView: NSView {
         self.segments = diffProvider(original, updated, mode)
         super.init(frame: .zero)
     }
+    #endif
 
     @available(*, unavailable, message: "Use init(original:updated:style:mode:)")
     required init?(coder: NSCoder) {
@@ -133,17 +150,44 @@ public final class NSTextDiffView: NSView {
         }
     }
 
-    private func updateSegmentsIfNeeded() {
+    /// Atomically updates view inputs and recomputes diff segments at most once.
+    public func setContent(
+        original: String,
+        updated: String,
+        style: TextDiffStyle,
+        mode: TextDiffComparisonMode
+    ) {
+        isBatchUpdating = true
+        defer {
+            isBatchUpdating = false
+            let needsStyleInvalidation = pendingStyleInvalidation
+            pendingStyleInvalidation = false
+
+            let didRecompute = updateSegmentsIfNeeded()
+            if needsStyleInvalidation, !didRecompute {
+                invalidateCachedLayout()
+            }
+        }
+
+        self.style = style
+        self.mode = mode
+        self.original = original
+        self.updated = updated
+    }
+
+    @discardableResult
+    private func updateSegmentsIfNeeded() -> Bool {
         let newModeKey = Self.modeKey(for: mode)
         guard original != lastOriginal || updated != lastUpdated || newModeKey != lastModeKey else {
-            return
+            return false
         }
 
         lastOriginal = original
         lastUpdated = updated
         lastModeKey = newModeKey
         segments = diffProvider(original, updated, mode)
         invalidateCachedLayout()
+        return true
     }
 
     private func layoutForCurrentWidth() -> DiffLayout {

Tests/TextDiffTests/NSTextDiffViewTests.swift

@@ -91,3 +91,53 @@ func nsTextDiffViewStyleChangeDoesNotRecomputeDiff() {
 
     #expect(callCount == 1)
 }
+
+@Test
+@MainActor
+func nsTextDiffViewSetContentBatchesRecompute() {
+    var callCount = 0
+    let view = NSTextDiffView(
+        original: "old",
+        updated: "new",
+        mode: .token
+    ) { _, _, _ in
+        callCount += 1
+        return [DiffSegment(kind: .equal, tokenKind: .word, text: "\(callCount)")]
+    }
+
+    var style = TextDiffStyle.default
+    style.deletionStrikethrough = true
+    view.setContent(
+        original: "old-2",
+        updated: "new-2",
+        style: style,
+        mode: .character
+    )
+
+    #expect(callCount == 2)
+}
+
+@Test
+@MainActor
+func nsTextDiffViewSetContentStyleOnlyDoesNotRecomputeDiff() {
+    var callCount = 0
+    let view = NSTextDiffView(
+        original: "old",
+        updated: "new",
+        mode: .token
+    ) { _, _, _ in
+        callCount += 1
+        return [DiffSegment(kind: .equal, tokenKind: .word, text: "\(callCount)")]
+    }
+
+    var style = TextDiffStyle.default
+    style.deletionStrikethrough = true
+    view.setContent(
+        original: "old",
+        updated: "new",
+        style: style,
+        mode: .token
+    )
+
+    #expect(callCount == 1)
+}