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(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.
      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))))