MD.ai/MarkdownViewer/MarkdownViewerApp.swift

import SwiftUI
import UniformTypeIdentifiers
import AppKit

@main
struct MarkdownViewerApp: App {
    var body: some Scene {
        Settings {
            EmptyView()
        }
        .commands {
            CommandGroup(replacing: .newItem) {
                Button("Open Markdown File...") {
                    openMarkdownFile()
                }
                .keyboardShortcut("o", modifiers: .command)
            }
        }
    }
    
    private func openMarkdownFile() {
        let panel = NSOpenPanel()
        panel.allowsMultipleSelection = true
        panel.canChooseDirectories = false
        panel.canChooseFiles = true
        panel.allowedContentTypes = [UTType.plainText, UTType(filenameExtension: "md")!]
        
        if panel.runModal() == .OK {
            for url in panel.urls {
                openNewWindow(for: url)
            }
        }
    }
    
    private func openNewWindow(for url: URL) {
        do {
            let content = try String(contentsOf: url, encoding: .utf8)
            let newWindow = NSWindow(
                contentRect: NSRect(x: 0, y: 0, width: 800, height: 600),
                styleMask: [.titled, .closable, .resizable, .miniaturizable],
                backing: .buffered,
                defer: false
            )
            
            newWindow.title = url.lastPathComponent
            newWindow.contentView = NSHostingView(
                rootView: MarkdownDocumentView(
                    content: content,
                    fileName: url.lastPathComponent
                )
            )
            newWindow.center()
            newWindow.makeKeyAndOrderFront(nil)
            
        } catch {
            print("Error reading file: \(error)")
            // Show error in a new window
            let newWindow = NSWindow(
                contentRect: NSRect(x: 0, y: 0, width: 400, height: 200),
                styleMask: [.titled, .closable],
                backing: .buffered,
                defer: false
            )
            
            newWindow.title = "Error"
            newWindow.contentView = NSHostingView(
                rootView: VStack {
                    Image(systemName: "exclamationmark.triangle")
                        .font(.system(size: 40))
                        .foregroundColor(.red)
                    Text("Error loading file")
                        .font(.headline)
                    Text(error.localizedDescription)
                        .font(.caption)
                        .foregroundColor(.secondary)
                        .multilineTextAlignment(.center)
                }
                .padding()
            )
            newWindow.center()
            newWindow.makeKeyAndOrderFront(nil)
        }
    }
}