fileprivate lazy var pages: [UIViewController] = {
    return [
        self.getViewController(withIdentifier: "BasicInfoViewController"),
        self.getViewController(withIdentifier: "AccountInfoViewController"),
        self.getViewController(withIdentifier: "ContactInfoViewController")
    ]
}()

fileprivate func getViewController(withIdentifier identifier: String) -> UIViewController {
    return UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: identifier)
}

override func viewDidLoad() {

    self.dataSource = self
    self.delegate = self

    if let firstVC = pages.first
    {
        setViewControllers([firstVC], direction: .forward, animated: true, completion: nil)
    }


    setupPageControl()

}

func setupPageControl(){
    let appearance = UIPageControl.appearance()
    appearance.pageIndicatorTintColor = UIColor.gray
    appearance.currentPageIndicatorTintColor = UIColor.blue
    appearance.backgroundColor = #colorLiteral(red: 0, green: 0, blue: 0, alpha: 1)
}

func presentationCount(for pageViewController: UIPageViewController) -> Int {
    return 3
}

func presentationIndex(for pageViewController: UIPageViewController) -> Int {
    return 0
}

//swipe backwards
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {

    guard let viewControllerIndex = pages.index(of: viewController) else { return nil }

    let previousIndex = viewControllerIndex - 1

    guard previousIndex >= 0 else { return pages.last }

    guard pages.count > previousIndex else { return nil }

    return pages[previousIndex]
}

//swipe forward
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController?
{
    guard let viewControllerIndex = pages.index(of: viewController) else { return nil }

    let nextIndex = viewControllerIndex + 1

    guard nextIndex < pages.count else { return pages.first }

    guard pages.count > nextIndex else { return nil }

    return pages[nextIndex]
}

func goToNextPage(){

    guard let currentViewController = self.viewControllers?.first else { return }

    guard let nextViewController = dataSource?.pageViewController( self, viewControllerAfterViewController: currentViewController ) else { return }

    setViewControllers([nextViewController], direction: .Forward, animated: false, completion: nil)

}


func goToPreviousPage(){

    guard let currentViewController = self.viewControllers?.first else { return }

    guard let previousViewController = dataSource?.pageViewController( self, viewControllerBeforeViewController: currentViewController ) else { return }

    setViewControllers([previousViewController], direction: .Reverse, animated: false, completion: nil)

}