feat: render interactive markdown task checkboxes

Sources/Conjure/NotesController.swift

@@ -7,7 +7,7 @@ final class NotesController: NSViewController, NSTextViewDelegate {
     private let browseButton = NSButton(title: "Browse Notes", target: nil, action: nil)
     private let actionsButton = NSButton(title: "Actions", target: nil, action: nil)
     private let actions = ApplicationActionsController()
-    private let editor = NSTextView()
+    private let editor = NotesTextView()
     private let status = NSTextField(labelWithString: "")
     private let defaults: UserDefaults
     private var store: NotesStore?
@@ -116,6 +116,7 @@ final class NotesController: NSViewController, NSTextViewDelegate {
     func textDidChange(_ notification: Notification) {
         isDirty = true
         MarkdownHighlighting.apply(to: editor)
+        editor.refreshTasks()
         _ = save()
     }
 
@@ -261,6 +262,7 @@ final class NotesController: NSViewController, NSTextViewDelegate {
         editor.isEditable = true
         editor.setSelectedRange(NSRange(location: editor.string.utf16.count, length: 0))
         MarkdownHighlighting.apply(to: editor)
+        editor.refreshTasks()
         status.stringValue = "Saved locally · Markdown · Paste or drop images"
         status.textColor = SunsetPalette.secondaryText
     }
@@ -297,6 +299,88 @@ private final class NotesView: NSView {
     }
 }
 
+@MainActor
+final class NotesTextView: NSTextView {
+    private struct Task {
+        let marker: NSRange
+        let state: NSRange
+        let checked: Bool
+        let title: String
+    }
+    private static let taskPattern = try! NSRegularExpression(
+        pattern: "(?m)^[ \\t]*((?:[-+*]|[0-9]+[.)])[ \\t]+\\[([ xX])\\])(?=[ \\t]|\\r?$)"
+    )
+    private var tasks: [Task] = []
+    private var checkboxes: [NSButton] = []
+
+    // ponytail: scan the whole note on edits; incremental parsing if large task lists make typing slow.
+    func refreshTasks() {
+        guard let layoutManager else { return }
+        let source = string as NSString
+        let range = NSRange(location: 0, length: source.length)
+        layoutManager.removeTemporaryAttribute(.foregroundColor, forCharacterRange: range)
+        let code = MarkdownHighlighting.codeBlocks(in: string)
+        tasks = Self.taskPattern.matches(in: string, range: range).compactMap { match in
+            guard !code.contains(where: { NSIntersectionRange($0.range, match.range).length > 0 }) else { return nil }
+            let end = NSMaxRange(source.lineRange(for: match.range))
+            let title = source.substring(with: NSRange(location: NSMaxRange(match.range), length: end - NSMaxRange(match.range)))
+                .trimmingCharacters(in: .whitespacesAndNewlines)
+            return Task(marker: match.range(at: 1), state: match.range(at: 2),
+                        checked: source.substring(with: match.range(at: 2)) != " ", title: title)
+        }
+        while checkboxes.count > tasks.count {
+            let checkbox = checkboxes.removeLast()
+            if window?.firstResponder === checkbox { window?.makeFirstResponder(self) }
+            checkbox.removeFromSuperview()
+        }
+        while checkboxes.count < tasks.count {
+            let checkbox = NSButton(checkboxWithTitle: "", target: self, action: #selector(toggleTask(_:)))
+            checkbox.controlSize = .small
+            checkbox.contentTintColor = SunsetPalette.accent
+            checkbox.sizeToFit()
+            checkboxes.append(checkbox)
+            addSubview(checkbox)
+        }
+        for (index, task) in tasks.enumerated() {
+            let checkbox = checkboxes[index]
+            checkbox.tag = index
+            checkbox.state = task.checked ? .on : .off
+            checkbox.isEnabled = isEditable
+            checkbox.setAccessibilityLabel(task.title.isEmpty ? "Task" : task.title)
+            checkbox.toolTip = task.title
+            layoutManager.addTemporaryAttribute(.foregroundColor, value: NSColor.clear, forCharacterRange: task.marker)
+        }
+        positionCheckboxes()
+    }
+
+    override func layout() {
+        super.layout()
+        positionCheckboxes()
+    }
+
+    private func positionCheckboxes() {
+        guard let layoutManager, let textContainer else { return }
+        layoutManager.ensureLayout(for: textContainer)
+        for (index, task) in tasks.enumerated() {
+            let glyphs = layoutManager.glyphRange(forCharacterRange: task.marker, actualCharacterRange: nil)
+            let rect = layoutManager.boundingRect(forGlyphRange: glyphs, in: textContainer)
+                .offsetBy(dx: textContainerOrigin.x, dy: textContainerOrigin.y)
+            let checkbox = checkboxes[index]
+            checkbox.setFrameOrigin(NSPoint(x: rect.minX, y: rect.midY - checkbox.frame.height / 2))
+        }
+    }
+
+    @objc private func toggleTask(_ sender: NSButton) {
+        guard isEditable, tasks.indices.contains(sender.tag) else { return }
+        let task = tasks[sender.tag]
+        let selection = selectedRange()
+        breakUndoCoalescing()
+        insertText(task.checked ? " " : "x", replacementRange: task.state)
+        breakUndoCoalescing()
+        setSelectedRange(selection)
+    }
+}
+
 @MainActor
 enum MarkdownHighlighting {
     // ponytail: whole-note highlighting; incremental parsing if large notes make typing slow.