main.m

#import <AVFoundation/AVFoundation.h>
#import <Cocoa/Cocoa.h>

// MARK: - Automation Script Source

static NSString *const kAutomationScript =
    @"on selectHeadPointerCamera(cameraName)\n"
     "    tell application \"System Settings\" to activate\n"
     "    open location "
     "\"x-apple.systempreferences:com.apple.Accessibility-Settings.extension?"
     "PointerControl\"\n"
     "    tell application \"System Events\"\n"
     "        tell application process \"System Settings\"\n"
     "            repeat until exists (window \"Pointer Control\")\n"
     "                delay 0.5\n"
     "            end repeat\n"
     "            tell window \"Pointer Control\"\n"
     "                try\n"
     "                    set rightGroup to group 1 of scroll area 1 of group "
     "1 of splitter group 1 of group 1\n"
     "                    set foundRow to missing value\n"
     "                    repeat with uiGroup in groups of rightGroup\n"
     "                        if (exists static text \"Head pointer\" of "
     "uiGroup) then\n"
     "                            set foundRow to uiGroup\n"
     "                            exit repeat\n"
     "                        end if\n"
     "                    end repeat\n"
     "                    if foundRow is missing value then\n"
     "                        display dialog \"Could not find 'Head pointer' "
     "settings row.\" buttons {\"OK\"} default button \"OK\"\n"
     "                        return\n"
     "                    end if\n"
     "                    click button 1 of foundRow\n"
     "                    repeat until exists sheet 1\n"
     "                        delay 0.1\n"
     "                    end repeat\n"
     "                    tell sheet 1\n"
     "                        if (exists button \"Camera Options…\" of group 1 "
     "of scroll area 1) then\n"
     "                            click button \"Camera Options…\" of group 1 "
     "of scroll area 1\n"
     "                            delay 0.5\n"
     "                        end if\n"
     "                        set foundPopup to missing value\n"
     "                        try\n"
     "                            set foundPopup to pop up button \"Camera\" "
     "of group 1 of scroll area 1\n"
     "                        on error\n"
     "                            try\n"
     "                                set foundPopup to pop up button 1 of "
     "group 1 of scroll area 1\n"
     "                            end try\n"
     "                        end try\n"
     "                        if foundPopup is not missing value then\n"
     "                            click foundPopup\n"
     "                            delay 0.2\n"
     "                            click menu item cameraName of menu 1 of "
     "foundPopup\n"
     "                        else\n"
     "                            display dialog \"Could not find Camera "
     "selection menu.\"\n"
     "                        end if\n"
     "                        if exists button \"OK\" then\n"
     "                            click button \"OK\"\n"
     "                        else if exists button \"Done\" then\n"
     "                            click button \"Done\"\n"
     "                        end if\n"
     "                    end tell\n"
     "                on error errMsg\n"
     "                    display dialog \"Automation Error: \" & errMsg\n"
     "                end try\n"
     "            end tell\n"
     "        end tell\n"
     "    end tell\n"
     "end selectHeadPointerCamera";

// MARK: - App Delegate

@interface AppDelegate : NSObject <NSApplicationDelegate>
@property(strong, nonatomic) NSStatusItem *statusItem;
@property(strong, nonatomic) AVCaptureDeviceDiscoverySession *discoverySession;
@end

@implementation AppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
  // Setup Status Item
  self.statusItem = [[NSStatusBar systemStatusBar]
      statusItemWithLength:NSVariableStatusItemLength];
  NSImage *image = [NSImage imageWithSystemSymbolName:@"video.fill"
                             accessibilityDescription:@"Camera Switcher"];
  self.statusItem.button.image = image;

  // Setup Discovery Session
  self.discoverySession = [AVCaptureDeviceDiscoverySession
      discoverySessionWithDeviceTypes:@[
        AVCaptureDeviceTypeBuiltInWideAngleCamera,
        AVCaptureDeviceTypeExternalUnknown
      ]
                            mediaType:AVMediaTypeVideo
                             position:AVCaptureDevicePositionUnspecified];

  // Build Menu
  [self constructMenu];

  // Notifications
  [[NSNotificationCenter defaultCenter]
      addObserver:self
         selector:@selector(rebuildMenu)
             name:AVCaptureDeviceWasConnectedNotification
           object:nil];
  [[NSNotificationCenter defaultCenter]
      addObserver:self
         selector:@selector(rebuildMenu)
             name:AVCaptureDeviceWasDisconnectedNotification
           object:nil];
}

- (void)rebuildMenu {
  dispatch_async(dispatch_get_main_queue(), ^{
    [self constructMenu];
  });
}

- (void)constructMenu {
  NSMenu *menu = [[NSMenu alloc] init];
  [menu addItemWithTitle:@"Head Pointer Camera" action:nil keyEquivalent:@""];
  [menu addItem:[NSMenuItem separatorItem]];

  NSArray<AVCaptureDevice *> *devices = self.discoverySession.devices;

  if (devices.count == 0) {
    [menu addItemWithTitle:@"No Cameras Found" action:nil keyEquivalent:@""];
  } else {
    for (AVCaptureDevice *device in devices) {
      NSMenuItem *item =
          [[NSMenuItem alloc] initWithTitle:device.localizedName
                                     action:@selector(cameraSelected:)
                              keyEquivalent:@""];
      item.target = self;
      item.representedObject = device.localizedName;
      [menu addItem:item];
    }
  }

  [menu addItem:[NSMenuItem separatorItem]];
  [menu addItemWithTitle:@"Quit" action:@selector(quitApp) keyEquivalent:@"q"];

  self.statusItem.menu = menu;
}

- (void)cameraSelected:(NSMenuItem *)sender {
  NSString *cameraName = sender.representedObject;
  NSLog(@"Switching to camera: %@", cameraName);

  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
                 ^{
                   [self runAutomationForCamera:cameraName];
                 });
}

- (void)runAutomationForCamera:(NSString *)cameraName {
  NSAppleScript *script =
      [[NSAppleScript alloc] initWithSource:kAutomationScript];

  // We need to call the handler "selectHeadPointerCamera(cameraName)"
  // NSAppleScript doesn't easily support calling handlers with arguments
  // directly without NSAppleEventDescriptor ceremony. Easier way: Append the
  // call to the script source dynamically.

  NSString *command = [NSString
      stringWithFormat:@"\nselectHeadPointerCamera(\"%@\")", cameraName];
  NSString *fullScript = [kAutomationScript stringByAppendingString:command];

  NSAppleScript *runScript = [[NSAppleScript alloc] initWithSource:fullScript];
  NSDictionary *errorInfo = nil;
  [runScript executeAndReturnError:&errorInfo];

  if (errorInfo) {
    NSLog(@"AppleScript Error: %@", errorInfo);
  }
}

- (void)quitApp {
  [NSApp terminate:nil];
}

@end

// MARK: - Main

int main(int argc, const char *argv[]) {
  @autoreleasepool {
    NSApplication *app = [NSApplication sharedApplication];
    AppDelegate *delegate = [[AppDelegate alloc] init];
    app.delegate = delegate;
    [app run];
  }
  return 0;
}