BarHideOnScroll - UIScrollViewDelegate

    var navBarOriginalHeight: CGFloat = 0.0
    let navBarMinHeight: CGFloat = 10.0
    var previousScrollViewYOffset: CGFloat = 0.0


// MARK: - UIScrollViewDelegate
    
    func scrollViewDidScroll(scrollView: UIScrollView) {
        guard scrollView.contentSize.height >= scrollView.frame.height else {return}
        guard let navigationBar = navigationController?.navigationBar else {return}
        guard scrollView.contentOffset.y > 100 else {return}
        
        // Calculate current YOffset but without elasticity
        let currentScrollViewYOffset: CGFloat = {
            let topInset = scrollView.contentInset.top
            let bottomInset = scrollView.contentInset.bottom
            let minYOffset = -topInset
            let maxYOffset = scrollView.contentSize.height + bottomInset - scrollView.frame.height
            return max(minYOffset, min(scrollView.contentOffset.y, maxYOffset))
        }()
        
        // delta content offset y, scroll up minus, scroll down plus
        let yDelta = previousScrollViewYOffset - currentScrollViewYOffset
        
        // Slide up nav bar
        let navOriginY = max(20.0 - 44.0, min(navigationBar.frame.origin.y + yDelta, 20.0))
        let navFrame = CGRectMake(0, navOriginY, navigationBar.frame.width, navigationBar.frame.height)
        navigationBar.frame = navFrame
        
        // Slide down tool bar
        if let toolBar = navigationController?.toolbar {
            let originY = max(view.frame.height - 44.0, min(toolBar.frame.origin.y - yDelta, view.frame.height))
            let frame = CGRectMake(0, originY, toolBar.frame.width, toolBar.frame.height)
            toolBar.frame = frame
        }
        
        // Shrink nav bar
        //let newNavBarHeight = max(navBarMinHeight, min(navigationBar.frame.height + yDelta, 44.0))
        //let navFrame = CGRectMake(0, navigationBar.frame.origin.y, navigationBar.frame.width, newNavBarHeight)
        //navigationBar.frame = navFrame
        
        updateNavBarItems()
        configureWebViewInsets()
        previousScrollViewYOffset = currentScrollViewYOffset
    }
    
    func scrollViewDidEndDragging(scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        stoppedScrolling()
    }
    
    func updateNavBarItems() {
        guard let navigationBar = navigationController?.navigationBar else {return}
        let min: CGFloat = 20.0 - 44.0
        let max: CGFloat = 20.0
        let alpha = (navigationBar.frame.origin.y - min) / (max - min)
        navigationItem.titleView?.alpha = alpha
    }
    
    func stoppedScrolling() {
        guard let navigationBar = navigationController?.navigationBar else {return}
        let show = ((navigationBar.frame.origin.y - (20-44)) / 44) > 0.5
        animateBar(show)
    }
    
    func animateBar(show: Bool) {
        UIView.animateWithDuration(0.2) { () -> Void in
            if show {
                if let navBar = self.navigationController?.navigationBar {
                    navBar.frame = CGRectMake(0, 20, navBar.frame.width, navBar.frame.height)
                }
                if let toolBar = self.navigationController?.toolbar {
                    toolBar.frame = CGRectMake(0, self.view.frame.height - toolBar.frame.height, toolBar.frame.width, toolBar.frame.height)
                }
                self.navigationItem.titleView?.alpha = 1.0
            } else {
                if let navBar = self.navigationController?.navigationBar {
                    navBar.frame = CGRectMake(0, 20 - 44, navBar.frame.width, navBar.frame.height)
                }
                if let toolBar = self.navigationController?.toolbar {
                    toolBar.frame = CGRectMake(0, self.view.frame.height, toolBar.frame.width, toolBar.frame.height)
                }
                self.navigationItem.titleView?.alpha = 0.0
            }
        }
    }