webview_objc.h

// will have to pass -x objective-c++ to the cgo compiler or to the C++ compiler
//
// ====================================================================
//
// This implementation uses Cocoa WKWebView backend on macOS. It is
// written using ObjC runtime and uses WKWebView class as a browser runtime.
// You should pass "-framework Webkit" flag to the compiler.
//
// ====================================================================
//

#include <CoreGraphics/CoreGraphics.h>
#include <objc/objc-runtime.h>

#define NSBackingStoreBuffered 2

#define NSWindowStyleMaskResizable 8
#define NSWindowStyleMaskMiniaturizable 4
#define NSWindowStyleMaskTitled 1
#define NSWindowStyleMaskClosable 2

#define NSApplicationActivationPolicyRegular 0

#define WKUserScriptInjectionTimeAtDocumentStart 0

namespace webview {

// Helpers to avoid too much typing
id operator"" _cls(const char *s, std::size_t) { return (id)objc_getClass(s); }
SEL operator"" _sel(const char *s, std::size_t) { return sel_registerName(s); }
id operator"" _str(const char *s, std::size_t) {
  return ((id(*)(id, SEL, const char *))objc_msgSend)(
      "NSString"_cls, "stringWithUTF8String:"_sel, s);
}

// needed to allow the callback below to have access to the window
id globalWindow;

// this performs an action once the WKWebView content  is loaded
// here we set the alpha of the window back to 1 to make it visible
void finished_navigation(id,SEL) {
    ((void (*)(id, SEL, double))objc_msgSend)(globalWindow, "setAlphaValue:"_sel, 1.0);
 }

 /* Delegate
#include <Cocoa/Cocoa.h>

@interface AppDelegate: NSResponder<NSTouchBarProvider>
@end

@implementation AppDelegate

-(BOOL)applicationShouldTerminateAfterLastWindowClosed:(id)sender {
    return true;
}

-(void)userContentController: (id)sender didReceiveScriptMessage:(WKScriptMessage*)msg {
    cocoa_wkwebview_engine* w = objc_getAssociatedObject(self, "webview");
    assert(w);
    w->on_message( [[ msg body ] UTF8String ] );
}

-(void)webview: (WKWebView*)w didFinishNavigation: (WKNavigation*)navigation {
    [ globalWindow setAlphaValue: 1.0 ];
}
 */

class cocoa_wkwebview_engine {
public:
  cocoa_wkwebview_engine(bool debug, void *window) {

    // Application
    // id app = [[NSApplication] sharedApplication];
    id app = ((id(*)(id, SEL))objc_msgSend)("NSApplication"_cls,
                                            "sharedApplication"_sel);
    // [ app setActivationPolicy: NSApplicationActivaionPolicyRegular];
    ((void (*)(id, SEL, long))objc_msgSend)(
        app, "setActivationPolicy:"_sel, NSApplicationActivationPolicyRegular);

    // Delegate
    auto cls =
        objc_allocateClassPair((Class) "NSResponder"_cls, "AppDelegate", 0);
    class_addProtocol(cls, objc_getProtocol("NSTouchBarProvider"));
    class_addMethod(cls, "applicationShouldTerminateAfterLastWindowClosed:"_sel,
                    (IMP)(+[](id, SEL, id) -> BOOL { return 1; }), "c@:@");
    class_addMethod(cls, "userContentController:didReceiveScriptMessage:"_sel,
                    (IMP)(+[](id self, SEL, id, id msg) {
                      auto w =
                          (cocoa_wkwebview_engine *)objc_getAssociatedObject(
                              self, "webview");
                      assert(w);
                      w->on_message(((const char *(*)(id, SEL))objc_msgSend)(
                          ((id(*)(id, SEL))objc_msgSend)(msg, "body"_sel),
                          "UTF8String"_sel));
                    }),
                    "v@:@@");
    objc_registerClassPair(cls);
    // AppDelegate* delegate = [AppDelegate new];
    auto delegate = ((id(*)(id, SEL))objc_msgSend)((id)cls, "new"_sel);
    // objc_setAssociatedObject(delegate, "webview", (id)this, OBJC_ASSOCIATION_ASSIGN);
    objc_setAssociatedObject(delegate, "webview", (id)this,
                             OBJC_ASSOCIATION_ASSIGN);

    //[ app setDelegate: delegate ];
    ((void (*)(id, SEL, id))objc_msgSend)(app, sel_registerName("setDelegate:"),
                                          delegate);
    // Main window
    if (window == nullptr) {
        //m_window = [[NSWindow alloc] initWithContentRect: CGREctMake(0,0,0,0) styleMask: 0 backing: NSBackingStoreBuffered defer: 0 ];
      m_window = ((id(*)(id, SEL))objc_msgSend)("NSWindow"_cls, "alloc"_sel);
      m_window =
          ((id(*)(id, SEL, CGRect, int, unsigned long, int))objc_msgSend)(
              m_window, "initWithContentRect:styleMask:backing:defer:"_sel,
              CGRectMake(0, 0, 0, 0), 0, NSBackingStoreBuffered, 0);
    } else {
      m_window = (id)window;
    }

    // Webview
    // id config = [WKWebViewConfiguration new];
    auto config =
        ((id(*)(id, SEL))objc_msgSend)("WKWebViewConfiguration"_cls, "new"_sel);
    //m_manager = [ config userContentController ];
    m_manager =
        ((id(*)(id, SEL))objc_msgSend)(config, "userContentController"_sel);
    //m_webview = [ WKWebView alloc ];
    m_webview = ((id(*)(id, SEL))objc_msgSend)("WKWebView"_cls, "alloc"_sel);

    if (debug) {
      // Equivalent Obj-C:
      // [[config preferences] setValue:@YES forKey:@"developerExtrasEnabled"];
      ((id(*)(id, SEL, id, id))objc_msgSend)(
          ((id(*)(id, SEL))objc_msgSend)(config, "preferences"_sel),
          "setValue:forKey:"_sel,
          ((id(*)(id, SEL, BOOL))objc_msgSend)("NSNumber"_cls,
                                               "numberWithBool:"_sel, 1),
          "developerExtrasEnabled"_str);
    }

    // Equivalent Obj-C:
    // [[config preferences] setValue:@YES forKey:@"fullScreenEnabled"];
    ((id(*)(id, SEL, id, id))objc_msgSend)(
        ((id(*)(id, SEL))objc_msgSend)(config, "preferences"_sel),
        "setValue:forKey:"_sel,
        ((id(*)(id, SEL, BOOL))objc_msgSend)("NSNumber"_cls,
                                             "numberWithBool:"_sel, 1),
        "fullScreenEnabled"_str);

    // Equivalent Obj-C:
    // [[config preferences] setValue:@YES forKey:@"javaScriptCanAccessClipboard"];
    ((id(*)(id, SEL, id, id))objc_msgSend)(
        ((id(*)(id, SEL))objc_msgSend)(config, "preferences"_sel),
        "setValue:forKey:"_sel,
        ((id(*)(id, SEL, BOOL))objc_msgSend)("NSNumber"_cls,
                                             "numberWithBool:"_sel, 1),
        "javaScriptCanAccessClipboard"_str);

    // Equivalent Obj-C:
    // [[config preferences] setValue:@YES forKey:@"DOMPasteAllowed"];
    ((id(*)(id, SEL, id, id))objc_msgSend)(
        ((id(*)(id, SEL))objc_msgSend)(config, "preferences"_sel),
        "setValue:forKey:"_sel,
        ((id(*)(id, SEL, BOOL))objc_msgSend)("NSNumber"_cls,
                                             "numberWithBool:"_sel, 1),
        "DOMPasteAllowed"_str);

    ((void (*)(id, SEL, CGRect, id))objc_msgSend)(
        m_webview, "initWithFrame:configuration:"_sel, CGRectMake(0, 0, 0, 0),
        config);
    ((void (*)(id, SEL, id, id))objc_msgSend)(
        m_manager, "addScriptMessageHandler:name:"_sel, delegate,
        "external"_str);

    init(R"script(
                      window.external = {
                        invoke: function(s) {
                          window.webkit.messageHandlers.external.postMessage(s);
                        },
                      };
                     )script");


    // fix white flash on startup
    // Make the window invisible before any content is loaded	
    // [ m_window setAlphaValue: 0.0];
    ((void(*)(id, SEL, double))objc_msgSend)(m_window, "setAlphaValue:"_sel, 0.0);
    // set globalWindow to a reference of m_window
    globalWindow = m_window;
    // add a finished_navigation method that peforms some action once the web content is loaded
    // Ths function is defined before the cocoa_wkwebview_engine class and it makes the window visible
    class_addMethod(objc_getClass("WKWebView"), "webView:didFinishNavigation:"_sel,(IMP) finished_navigation, "v@:@");
    // this bit is required to make sure our callback is called
    // reuse the AppDelegate?
    //[ m_webview setNavigationDelegate: delegate ];
    //[ m_webview setNavigationDelegate: m_webview ];
    ((void(*)(id, SEL, id))objc_msgSend)(m_webview, "setNavigationDelegate:"_sel, m_webview);

    // Equivalent Obj-C:
    // [ webView setValue:@NO forKey:@"drawsBackground"];
    ((void(*)(id, SEL, id, id))objc_msgSend)(m_webview, "setValue:forKey:"_sel,((id(*)(id, SEL, BOOL))objc_msgSend)("NSNumber"_cls,
                                             "numberWithBool:"_sel, 0) , "drawsBackground"_str);
    // [ m_window setContentView: m_webview ] ;
    ((void (*)(id, SEL, id))objc_msgSend)(m_window, "setContentView:"_sel,
                                          m_webview);
    // [ m_window makeKeyAndOrderFront: nil ];
    ((void (*)(id, SEL, id))objc_msgSend)(m_window, "makeKeyAndOrderFront:"_sel,
                                          nullptr);

  }
  ~cocoa_wkwebview_engine() { close(); }
  void *window() { return (void *)m_window; }
  void terminate() {
    close();
    // [ NSApp terminate: nil];
    ((void (*)(id, SEL, id))objc_msgSend)("NSApp"_cls, "terminate:"_sel,
                                          nullptr);
  }
  void run() {
    // id app = [ NSApplication sharedApplication ];
    id app = ((id(*)(id, SEL))objc_msgSend)("NSApplication"_cls,
                                            "sharedApplication"_sel);
    dispatch([&]() {
       // [ app activateIgnoringOtherApps: 1];
      ((void (*)(id, SEL, BOOL))objc_msgSend)(
          app, "activateIgnoringOtherApps:"_sel, 1);
    });
    // [ app run ];
    ((void (*)(id, SEL))objc_msgSend)(app, "run"_sel);
  }
  void dispatch(std::function<void()> f) {
    dispatch_async_f(dispatch_get_main_queue(), new dispatch_fn_t(f),
                     (dispatch_function_t)([](void *arg) {
                       auto f = static_cast<dispatch_fn_t *>(arg);
                       (*f)();
                       delete f;
                     }));
  }
  void set_title(const std::string title) {
    // [ m_window setTitle: [NSString stringWithUTF8String: title.c_str()] ];
    ((void (*)(id, SEL, id))objc_msgSend)(
        m_window, "setTitle:"_sel,
        ((id(*)(id, SEL, const char *))objc_msgSend)(
            "NSString"_cls, "stringWithUTF8String:"_sel, title.c_str()));
  }
  void set_size(int width, int height, int hints) {
    // setting the size of a window on mac doesn't take into consideration the title bar,s o if the style mask is titled then it needs to be added to the height
    // TODO allow the user to customize style mask, maybe I want a window without native title bars so I can design my own
    const auto mac_title_bar = 22;
    height += mac_title_bar;
    auto style = NSWindowStyleMaskTitled | NSWindowStyleMaskClosable |
                 NSWindowStyleMaskMiniaturizable;
    if (hints != WEBVIEW_HINT_FIXED) {
      style = style | NSWindowStyleMaskResizable;
    }
    //[ m_window setStyleMask: style ];
    ((void (*)(id, SEL, unsigned long))objc_msgSend)(
        m_window, "setStyleMask:"_sel, style);

    if (hints == WEBVIEW_HINT_MIN) {
        //[ m_window setContentMinSize: CGSizeMake(width, height)];
      ((void (*)(id, SEL, CGSize))objc_msgSend)(
          m_window, "setContentMinSize:"_sel, CGSizeMake(width, height));
    } else if (hints == WEBVIEW_HINT_MAX) {
        //[ m_window setContentMaxSize: CGSizeMake(width, height)];
      ((void (*)(id, SEL, CGSize))objc_msgSend)(
          m_window, "setContentMaxSize:"_sel, CGSizeMake(width, height));
    } else {
        //[ m_window setFrame: CGRectMake(0,0,width,height) display: 1 animate: 0 ];
      ((void (*)(id, SEL, CGRect, BOOL, BOOL))objc_msgSend)(
          m_window, "setFrame:display:animate:"_sel,
          CGRectMake(0, 0, width, height), 1, 0);
    }

  }

  void navigate(const std::string url) {
      //NSURL* nsurl = [ NSURL URLWithString: [ NSString stringWithUTF8String: url.c_str() ] ];
    auto nsurl = ((id(*)(id, SEL, id))objc_msgSend)(
        "NSURL"_cls, "URLWithString:"_sel,
        ((id(*)(id, SEL, const char *))objc_msgSend)(
            "NSString"_cls, "stringWithUTF8String:"_sel, url.c_str()));
    //[ m_webview loadRequest: [ NSURLRequest requestWithURL: nsurl ] ];
    ((void (*)(id, SEL, id))objc_msgSend)(
        m_webview, "loadRequest:"_sel,
        ((id(*)(id, SEL, id))objc_msgSend)("NSURLRequest"_cls,
                                           "requestWithURL:"_sel, nsurl));
  }
  void init(const std::string js) {
    // Equivalent Obj-C:
    // [m_manager addUserScript:[[WKUserScript alloc] initWithSource:[NSString stringWithUTF8String:js.c_str()] injectionTime:WKUserScriptInjectionTimeAtDocumentStart forMainFrameOnly:YES]]
    ((void (*)(id, SEL, id))objc_msgSend)(
        m_manager, "addUserScript:"_sel,
        ((id(*)(id, SEL, id, long, BOOL))objc_msgSend)(
            ((id(*)(id, SEL))objc_msgSend)("WKUserScript"_cls, "alloc"_sel),
            "initWithSource:injectionTime:forMainFrameOnly:"_sel,
            ((id(*)(id, SEL, const char *))objc_msgSend)(
                "NSString"_cls, "stringWithUTF8String:"_sel, js.c_str()),
            WKUserScriptInjectionTimeAtDocumentStart, 1));
  }
  void eval(const std::string js) {
      //[ m_webview evaluateJavaScript: [ NSString stringWithUTF8String: js.c_str() ] completionHandler: nullptr ];
    ((void (*)(id, SEL, id, id))objc_msgSend)(
        m_webview, "evaluateJavaScript:completionHandler:"_sel,
        ((id(*)(id, SEL, const char *))objc_msgSend)(
            "NSString"_cls, "stringWithUTF8String:"_sel, js.c_str()),
        nullptr);
  }

  void topmost(bool make_topmost = true) {
      auto level = make_topmost ? 3 : 0;
      //[ m_window setLevel: level ];
      ((void(*)(id, SEL,int))objc_msgSend)(m_window, "setLevel:"_sel, level);
  }

  void set_position(int x, int y) {
      //[ m_window setFrameTopLeftPoint: CGPointMake(x,y) ];
    ((void(*)(id, SEL, CGPoint))objc_msgSend)(m_window, "setFrameTopLeftPoint:"_sel, CGPointMake(x,y));
    return;
  }

  void center() {
    // places window slightly above center vertically
    //[ m_window center ];
    ((void(*)(id, SEL))objc_msgSend)(m_window, "center"_sel);
  }

private:
  virtual void on_message(const std::string msg) = 0;
    //void close() { [ m_window close ]; }
  void close() { ((void (*)(id, SEL))objc_msgSend)(m_window, "close"_sel); }
  id m_window;
  id m_webview;
  id m_manager;
};

using browser_engine = cocoa_wkwebview_engine;

} // namespace webview