Add selection-aware custom menu items

Package.swift

@@ -147,6 +147,7 @@ let package = Package(
         .testTarget(
             name: "MarkdownViewTests",
             dependencies: [
+                "Litext",
                 "MarkdownView",
                 "MarkdownParser",
             ]

README.md

@@ -315,7 +315,11 @@ Text selection is enabled by default. Long-press to select text, then use the st
 
 ```swift
 markdownView.textView.customMenuItems = [
-    LTXCustomMenuItem(title: "Explain", image: UIImage(systemName: "lightbulb")) { context in
+    LTXCustomMenuItem(
+        title: "Explain",
+        image: UIImage(systemName: "lightbulb"),
+        isAvailable: { !$0.text.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty }
+    ) { context in
         print("Explain: \(context.text) (lines \(context.startLine)-\(context.endLine))")
     },
     LTXCustomMenuItem(title: "Apply", image: UIImage(systemName: "checkmark.circle")) { context in
@@ -326,7 +330,7 @@ markdownView.textView.customMenuItems = [
 
 </details>
 
-Custom items appear after the built-in Copy, Select All, and Share actions. On iOS they integrate with `UIMenuController`, on Mac Catalyst with `UIContextMenuInteraction`, and on macOS with `NSMenu`.
+Custom items appear after the built-in Copy, Select All, and Share actions. Use `isAvailable` to show mutually exclusive commands for different selected ranges; it is reevaluated while the user drags the selection handles. Set `selectionChangeHandler` when the surrounding UI also needs the live selected range. On iOS custom actions integrate with `UIMenuController`, on Mac Catalyst with `UIContextMenuInteraction`, and on macOS with `NSMenu`.
 
 #### Line Selection (Opt-in)
 

Sources/Litext/LTXLabel/Interaction/LTXLabel+Interaction@AppKit.swift

@@ -182,6 +182,9 @@ import Foundation
 
         private func showContextMenu() {
             let menu = NSMenu()
+            let availableCustomItems = selectionContext().map { context in
+                customMenuItems.filter { $0.isAvailable(context) }
+            } ?? []
 
             let addBuiltIn = {
                 menu.addItem(
@@ -192,9 +195,12 @@ import Foundation
             }
 
             let addCustom = { [self] in
-                for customItem in self.customMenuItems {
+                for customItem in availableCustomItems {
                     menu.addItem(withTitle: customItem.title, image: customItem.image) { [weak self] in
-                        guard let self, let context = self.selectionContext() else { return }
+                        guard let self,
+                              let context = self.selectionContext(),
+                              customItem.isAvailable(context)
+                        else { return }
                         customItem.handler(context)
                     }
                 }
@@ -203,11 +209,11 @@ import Foundation
             switch customMenuItemPosition {
             case .beforeBuiltIn:
                 addCustom()
-                if !customMenuItems.isEmpty { menu.addItem(.separator()) }
-                addBuiltIn()
+                if !availableCustomItems.isEmpty { menu.addItem(.separator()) }
+                _ = addBuiltIn()
             case .afterBuiltIn:
-                addBuiltIn()
-                if !customMenuItems.isEmpty { menu.addItem(.separator()) }
+                _ = addBuiltIn()
+                if !availableCustomItems.isEmpty { menu.addItem(.separator()) }
                 addCustom()
             }
 

Sources/Litext/LTXLabel/Interaction/LTXLabel+Touches.swift

@@ -251,8 +251,10 @@
                         guard canPerformAction(selector, withSender: nil) else { return nil }
                         return UIMenuItem(title: item.title, action: selector)
                     }
+                let context = selectionContext()
                 for (index, customItem) in customMenuItems.enumerated() {
                     guard index < Self.customMenuSelectors.count else { break }
+                    guard let context, customItem.isAvailable(context) else { continue }
                     let selector = Self.customMenuSelectors[index]
                     items.append(UIMenuItem(title: customItem.title, action: selector))
                 }
@@ -295,7 +297,9 @@
                 guard index < customMenuItems.count,
                       let context = selectionContext()
                 else { return }
-                customMenuItems[index].handler(context)
+                let item = customMenuItems[index]
+                guard item.isAvailable(context) else { return }
+                item.handler(context)
             }
 
             @objc func copyMenuItemTapped() {
@@ -353,6 +357,7 @@
                     return index < customMenuItems.count
                         && selectionRange != nil
                         && selectionRange!.length > 0
+                        && selectionContext().map(customMenuItems[index].isAvailable) == true
                 }
                 return false
             }

Sources/Litext/LTXLabel/Interaction/LTXLabel+UIContextMenuInteractionDelegate.swift

@@ -25,9 +25,13 @@
                             self.perform(selector)
                         }
                     }
-                let customActions: [UIMenuElement] = self.customMenuItems.map { customItem in
-                    UIAction(title: customItem.title, image: customItem.image) { [weak self] _ in
-                        guard let self, let context = self.selectionContext() else { return }
+                let context = selectionContext()
+                let customActions: [UIMenuElement] = self.customMenuItems.compactMap { customItem in
+                    guard let context, customItem.isAvailable(context) else { return nil }
+                    return UIAction(title: customItem.title, image: customItem.image) { [weak self] _ in
+                        guard let self, let context = self.selectionContext(), customItem.isAvailable(context) else {
+                            return
+                        }
                         customItem.handler(context)
                     }
                 }

Sources/Litext/LTXLabel/LTXLabel.swift

@@ -160,10 +160,10 @@ public class LTXLabel: LTXPlatformView, Identifiable {
 
     public internal(set) var selectionRange: NSRange? {
         didSet {
-            updateSelectionLayer()
             if selectionRange != oldValue {
                 delegate?.ltxLabelSelectionDidChange(self, selection: selectionRange)
             }
+            updateSelectionLayer()
         }
     }
 

Sources/Litext/LTXLabel/Menu/LTXCustomMenuItem.swift

@@ -36,11 +36,21 @@ public struct LTXSelectionContext {
 public struct LTXCustomMenuItem {
     public let title: String
     public let image: PlatformImage?
+    /// Determines whether the item is included for the current selection.
+    /// Evaluated every time the selection range changes, including while the
+    /// user drags either selection handle.
+    public let isAvailable: (LTXSelectionContext) -> Bool
     public let handler: (LTXSelectionContext) -> Void
 
-    public init(title: String, image: PlatformImage? = nil, handler: @escaping (LTXSelectionContext) -> Void) {
+    public init(
+        title: String,
+        image: PlatformImage? = nil,
+        isAvailable: @escaping (LTXSelectionContext) -> Bool = { _ in true },
+        handler: @escaping (LTXSelectionContext) -> Void
+    ) {
         self.title = title
         self.image = image
+        self.isAvailable = isAvailable
         self.handler = handler
     }
 }

Sources/MarkdownView/MarkdownTextView/MarkdownTextView+LTXDelegate.swift

@@ -11,8 +11,8 @@ import Litext
     import UIKit
 
     extension MarkdownTextView: LTXLabelDelegate {
-        public func ltxLabelSelectionDidChange(_: Litext.LTXLabel, selection _: NSRange?) {
-            // reserved for future use
+        public func ltxLabelSelectionDidChange(_: Litext.LTXLabel, selection: NSRange?) {
+            selectionChangeHandler?(selection)
         }
 
         public func ltxLabelDetectedUserEventMovingAtLocation(_ label: Litext.LTXLabel, location: CGPoint) {
@@ -71,8 +71,8 @@ import Litext
     import AppKit
 
     extension MarkdownTextView: LTXLabelDelegate {
-        public func ltxLabelSelectionDidChange(_: Litext.LTXLabel, selection _: NSRange?) {
-            // reserved for future use
+        public func ltxLabelSelectionDidChange(_: Litext.LTXLabel, selection: NSRange?) {
+            selectionChangeHandler?(selection)
         }
 
         public func ltxLabelDetectedUserEventMovingAtLocation(_ label: Litext.LTXLabel, location: CGPoint) {

Sources/MarkdownView/MarkdownTextView/MarkdownTextView.swift

@@ -23,6 +23,9 @@ enum ContentPipelineMode {
         public var codePreviewHandler: ((String?, NSAttributedString) -> Void)?
         public var lineSelectionHandler: LineSelectionHandler?
         public var lineSelectionEndedHandler: LineSelectionHandler?
+        /// Called whenever the selected character range changes, including
+        /// while either selection handle is being dragged.
+        public var selectionChangeHandler: ((NSRange?) -> Void)?
 
         public internal(set) var document: PreprocessedContent = .init()
         public let textView: LTXLabel = .init()
@@ -229,6 +232,8 @@ enum ContentPipelineMode {
         public var codePreviewHandler: ((String?, NSAttributedString) -> Void)?
         public var lineSelectionHandler: LineSelectionHandler?
         public var lineSelectionEndedHandler: LineSelectionHandler?
+        /// Called whenever the selected character range changes.
+        public var selectionChangeHandler: ((NSRange?) -> Void)?
 
         public internal(set) var document: PreprocessedContent = .init()
         public let textView: LTXLabel = .init()

Tests/MarkdownViewTests/SelectionMenuTests.swift

@@ -0,0 +1,52 @@
+import XCTest
+@testable import Litext
+
+@MainActor
+final class SelectionMenuTests: XCTestCase {
+    func testCustomMenuItemAvailabilityUsesCurrentSelection() {
+        let label = LTXLabel()
+        label.isSelectable = true
+        label.attributedText = NSAttributedString(string: "highlighted plain")
+
+        let item = LTXCustomMenuItem(
+            title: "Unhighlight",
+            isAvailable: { $0.range.location < 11 },
+            handler: { _ in }
+        )
+
+        label.selectionRange = NSRange(location: 0, length: 11)
+        XCTAssertTrue(item.isAvailable(try XCTUnwrap(label.selectionContext())))
+
+        label.selectionRange = NSRange(location: 12, length: 5)
+        XCTAssertFalse(item.isAvailable(try XCTUnwrap(label.selectionContext())))
+    }
+
+    func testSelectionChangeDelegateRunsBeforeSelectionLayerUpdate() {
+        let label = LTXLabel()
+        label.isSelectable = true
+        label.attributedText = NSAttributedString(string: "text")
+        let delegate = SelectionDelegateSpy()
+        label.delegate = delegate
+
+        label.selectionRange = NSRange(location: 0, length: 4)
+
+        XCTAssertEqual(delegate.selections, [NSRange(location: 0, length: 4)])
+    }
+}
+
+@MainActor
+private final class SelectionDelegateSpy: LTXLabelDelegate {
+    var selections: [NSRange?] = []
+
+    func ltxLabelSelectionDidChange(_ ltxLabel: LTXLabel, selection: NSRange?) {
+        selections.append(selection)
+    }
+
+    func ltxLabelDidTapOnHighlightContent(
+        _ ltxLabel: LTXLabel,
+        region: LTXHighlightRegion?,
+        location: CGPoint
+    ) {}
+
+    func ltxLabelDetectedUserEventMovingAtLocation(_ ltxLabel: LTXLabel, location: CGPoint) {}
+}