Preview SwiftUI layouts using Emacs org blocks

ob-swiftui.el

(use-package org
  :hook ((org-mode . org-display-inline-images))
  :config

  (use-package ob
    :bind (:map org-mode-map
                ("C-c C-c" . org-ctrl-c-ctrl-c))
    :config

    (use-package ob-swift
      :ensure t
      :config
      (org-babel-do-load-languages 'org-babel-load-languages
                                   (append org-babel-load-languages
                                           '((swift     . t))))

      (defun ar/org-refresh-inline-images ()
        (when org-inline-image-overlays
          (org-redisplay-inline-images)))

      ;; Automatically refresh inline images.
      (add-hook 'org-babel-after-execute-hook 'ar/org-refresh-inline-images)

      (defun adviced:org-babel-execute:swift (f &rest args)
        "Advice `adviced:org-babel-execute:swift' enabling swiftui header param."
        (let* ((body (nth 0 args))
               (params (nth 1 args))
               (swiftui (cdr (assoc :swiftui params)))
               (output))
          (when swiftui
            (assert (or (string-equal swiftui "preview")
                        (string-equal swiftui "interactive"))
                    nil ":swiftui must be either preview or interactive")
            (setq body (format
                        "
import Cocoa
import SwiftUI
import Foundation
let screenshotURL: URL = URL(fileURLWithPath: NSTemporaryDirectory(), isDirectory: true).appendingPathComponent(ProcessInfo.processInfo.globallyUniqueString + \".png\")
let preview = %s

NSApplication.shared.run {
  %s
}
extension NSApplication {
    public func run<V: View>(@ViewBuilder view: () -> V) {
        let appDelegate = AppDelegate(view())
        NSApp.setActivationPolicy(.regular)
        mainMenu = customMenu
        delegate = appDelegate
        run()
    }
}
extension NSApplication {
    var customMenu: NSMenu {
        let appMenu = NSMenuItem()
        appMenu.submenu = NSMenu()
        let quitItem = NSMenuItem(
            title: \"Quit \(ProcessInfo.processInfo.processName)\",
            action: #selector(NSApplication.terminate(_:)), keyEquivalent: \"q\")
        quitItem.keyEquivalentModifierMask = []
        appMenu.submenu?.addItem(quitItem)
        let mainMenu = NSMenu(title: \"Main Menu\")
        mainMenu.addItem(appMenu)
        return mainMenu
    }
}
class AppDelegate<V: View>: NSObject, NSApplicationDelegate, NSWindowDelegate {
    var window = NSWindow(
        contentRect: NSRect(x: 0, y: 0, width: 414 * 0.2, height: 896 * 0.2),
        styleMask: [.titled, .closable, .miniaturizable, .resizable, .fullSizeContentView],
        backing: .buffered, defer: false)
    var contentView: V
    init(_ contentView: V) {
        self.contentView = contentView
    }
    func applicationDidFinishLaunching(_ notification: Notification) {
        window.delegate = self
        window.center()
        window.contentView = NSHostingView(rootView: contentView)
        window.makeKeyAndOrderFront(nil)
        if preview {
            screenshot(view: window.contentView!, saveTo: screenshotURL)
            // Write path (without newline) so org babel can parse it
            // and also drop first chars (file://).
            print(screenshotURL.path, terminator: \"\")
            NSApplication.shared.terminate(self)
            return
        }
        window.setFrameAutosaveName(\"Main Window\")
        NSApp.activate(ignoringOtherApps: true)
    }
}
func screenshot(view: NSView, saveTo fileURL: URL) {
    let rep = view.bitmapImageRepForCachingDisplay(in: view.bounds)!
    view.cacheDisplay(in: view.bounds, to: rep)
    let pngData = rep.representation(using: .png, properties: [:])
    try! pngData?.write(to: fileURL)
}
"
                        (if (string-equal swiftui "preview")
                            "true"
                          "false")
                        body))
            (setq args (list body params)))
          (setq output (apply f args))
          (when org-inline-image-overlays
            (org-redisplay-inline-images))
          output))

      (advice-add #'org-babel-execute:swift
                  :around
                  #'adviced:org-babel-execute:swift))))