MArkDownText.swift

import AppKit
import Down
import Highlightr

struct MarkdownTextView: NSViewRepresentable {
   let markdown: String

   func makeNSView(context: Context) -> NSScrollView {
       let scrollView = NSScrollView()
       scrollView.hasVerticalScroller = true
       scrollView.autoresizingMask = [.width, .height]

       let textView = context.coordinator.textView
       textView.minSize = NSSize(width: 0, height: 0)
       textView.maxSize = NSSize(width: CGFloat.greatestFiniteMagnitude, height: CGFloat.greatestFiniteMagnitude)
       textView.isVerticallyResizable = true
       textView.isHorizontallyResizable = false
       textView.autoresizingMask = [.width]
       textView.textContainer?.widthTracksTextView = true
       
       scrollView.documentView = textView
       return scrollView
   }

   func updateNSView(_ nsView: NSScrollView, context: Context) {
       context.coordinator.updateText(markdown: markdown)
   }

   func makeCoordinator() -> Coordinator {
       Coordinator()
   }

   class Coordinator: NSObject {
       let textView = NSTextView()
       let highlightr = Highlightr()

       override init() {
           super.init()
           textView.isEditable = false
           textView.isSelectable = true
           textView.textContainerInset = NSSize(width: 10, height: 10)
           highlightr?.setTheme(to: "atom-one-dark")
       }

       func updateText(markdown: String) {
           DispatchQueue.global(qos: .userInitiated).async {
               do {
                   let down = Down(markdownString: markdown)
                   let attributedString = try down.toAttributedString()
                   
                   let highlightedAttributedString = NSMutableAttributedString(attributedString: attributedString)
                   self.applySyntaxHighlighting(to: highlightedAttributedString)
                   
                   DispatchQueue.main.async {
                       self.textView.textStorage?.setAttributedString(highlightedAttributedString)
                       self.textView.scrollRangeToVisible(NSRange(location: self.textView.string.count, length: 0))
                   }
               } catch {
                   DispatchQueue.main.async {
                       self.textView.string = "Failed to parse markdown: \(error)"
                   }
               }
           }
       }

       func applySyntaxHighlighting(to attributedString: NSMutableAttributedString) {
           let fullRange = NSRange(location: 0, length: attributedString.length)
           attributedString.enumerateAttribute(.font, in: fullRange, options: []) { value, range, _ in
               if let font = value as? NSFont, font.fontDescriptor.symbolicTraits.contains(.monoSpace) {
                   let code = attributedString.attributedSubstring(from: range).string
                   if let highlightedCode = highlightr?.highlight(code, as: "swift") {
                       attributedString.replaceCharacters(in: range, with: highlightedCode)
                   }
               }
           }
       }
   }
}