- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.scrollView.delegate = self;
    self.scrollView.maximumZoomScale = 5.0f;

    UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleTap:)];
    tapGesture.delegate = self;
    tapGesture.numberOfTapsRequired = 1;
    tapGesture.numberOfTouchesRequired = 1;
    [self.scrollView addGestureRecognizer:tapGesture];
}

#pragma mark - UIScrollView Delegate

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
    return self.imageView;
}

#pragma mark - UIGestureRecognizer Delegate

- (void)handleTap:(UITapGestureRecognizer *)tapGestur
{
    NSLog(@"%s", __PRETTY_FUNCTION__);

    if (tapGestur.state == UIGestureRecognizerStateEnded) {

        [UIView transitionWithView:self.imageView duration:1 options:UIViewAnimationOptionTransitionFlipFromRight|UIViewAnimationOptionCurveEaseInOut animations:^{
            if (!flipped) {
                self.imageView.image = [UIImage imageNamed:@"2-IPAD-P.jpg"];
                flipped = YES;
            }
            else {
                self.imageView.image = [UIImage imageNamed:@"1-IPAD-P.jpg"];
            }
        } completion:^(BOOL finished) {
            //
        }];
    }
}