gistfile1.m

#import <CoreGraphics/CoreGraphics.h>
#import <Foundation/Foundation.h>
#import <objc/runtime.h>
#import <objc/message.h>
#import <dlfcn.h>

__attribute__((constructor)) static void init(void) {
    
    Method bundleIdentifierMethod = class_getInstanceMethod(objc_getClass("NSBundle"), sel_registerName("bundleIdentifier"));
    IMP newImp = imp_implementationWithBlock(^(id self) {
        return @"com.foo";
    });
    
    method_setImplementation(bundleIdentifierMethod, newImp);
}

int main(int argc, char * argv[]) {
    
    @autoreleasepool {
        
        void *graphics_services = dlopen("/System/Library/PrivateFrameworks/GraphicsServices.framework/GraphicsServices", RTLD_LAZY);
        void *_GSInitialize = dlsym(graphics_services, "GSInitialize");
        void *_GSEventInitialize = dlsym(graphics_services, "GSEventInitialize");
        void *_GSEventPushRunLoopMode = dlsym(graphics_services, "GSEventPushRunLoopMode");
        void *_GSSetMainScreenInfo = dlsym(graphics_services, "GSSetMainScreenInfo");
        ((void (*)(void))_GSInitialize)();
        
        void *bks = dlopen("/System/Library/PrivateFrameworks/BackBoardServices.framework/BackBoardServices", RTLD_LAZY);
        void *_BKSDisplayServicesStart = dlsym(bks, "BKSDisplayServicesStart");
        ((void (*)(void))_BKSDisplayServicesStart)();
        
        void *uikit = dlopen("/System/Library/Frameworks/UIKit.framework/UIKit", RTLD_LAZY);
        void *_UIApplicationInitialize = dlsym(uikit, "UIApplicationInitialize");
        void *_UIApplicationInstantiateSingleton = dlsym(uikit, "UIApplicationInstantiateSingleton");
        ((void (*)(void))_UIApplicationInitialize)();
        
        id mainScreen = ((id (*)(id, SEL))objc_msgSend)(objc_getClass("UIScreen"), sel_registerName("mainScreen"));
        CGRect mainScreenBounds = ((CGRect (*)(id, SEL))objc_msgSend)(mainScreen, sel_registerName("bounds"));
        CGFloat mainScreenScale = ((CGFloat (*)(id, SEL))objc_msgSend)(mainScreen, sel_registerName("scale"));
        ((void (*)(CGSize, CGFloat, int))_GSSetMainScreenInfo)(mainScreenBounds.size, mainScreenScale, 0);
        
        Class mockAppClass = objc_allocateClassPair(objc_getClass("UIApplication"), "MockApp", 0);
        objc_registerClassPair(mockAppClass);
        class_addProtocol(mockAppClass, objc_getProtocol("UIApplicationDelegate"));
        
        ((void (*)(Class))_UIApplicationInstantiateSingleton)(mockAppClass);
        ((void (*)(BOOL))_GSEventInitialize)(NO);
        ((void (*)(CFRunLoopMode))_GSEventPushRunLoopMode)(kCFRunLoopDefaultMode);
        
        id UIApp = ((id (*)(id, SEL))objc_msgSend)(mockAppClass, sel_registerName("sharedApplication"));
        ((void (*)(id, SEL))objc_msgSend)(UIApp, sel_registerName("_accessibilityInit"));
        
        id mainCADisplay = ((id (*)(id, SEL))objc_msgSend)(mainScreen, sel_registerName("_display"));
        id displayConfiguration = [objc_getClass("FBSDisplayConfiguration") alloc];
        displayConfiguration = ((id (*)(id, SEL, id, BOOL))objc_msgSend)(displayConfiguration, sel_registerName("initWithCADisplay:isMainDisplay:"), mainCADisplay, YES);
        
        id rootWindow = [objc_getClass("UIRootSceneWindow") alloc];
        rootWindow = ((id (*)(id, SEL, id))objc_msgSend)(rootWindow, sel_registerName("initWithDisplayConfiguration:"), displayConfiguration);
        
        ((void (*)(id, SEL, CGRect))objc_msgSend)(rootWindow, sel_registerName("setFrame:"), CGRectMake(100, 100, 200, 200));
        id blueColor = ((id (*)(id, SEL))objc_msgSend)(objc_getClass("UIColor"), sel_registerName("blueColor"));
        ((void (*)(id, SEL, id))objc_msgSend)(rootWindow, sel_registerName("setBackgroundColor:"), blueColor);
        ((void (*)(id, SEL, BOOL))objc_msgSend)(rootWindow, sel_registerName("setHidden:"), NO);
        ((void (*)(id, SEL, int))objc_msgSend)(rootWindow, sel_registerName("setWindowLevel:"), 9999);
        
        NSLog(@"presenting window: %@", rootWindow);
        CFRunLoopRun();
        
        return 0;
    }
}