import SwiftUI
import UIKit

class SomePageVC: UIViewController {
	let theLabel = UILabel()
	override func viewDidLoad() {
		super.viewDidLoad()
		theLabel.translatesAutoresizingMaskIntoConstraints = false
		view.addSubview(theLabel)
		NSLayoutConstraint.activate([
			theLabel.centerXAnchor.constraint(equalTo: view.centerXAnchor),
			theLabel.centerYAnchor.constraint(equalTo: view.centerYAnchor),
		])
		theLabel.font = .systemFont(ofSize: 60.0, weight: .light)
	}
}
class CustomPageViewController: UIPageViewController, UIPageViewControllerDelegate, UIPageViewControllerDataSource {
	
	func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {

		guard let index = viewControllersList.firstIndex(of: viewController), index > 0 else {
			return nil
		}
		if let vc = viewControllersList[index - 1] as? SomePageVC {
			print("viewControllerBefore:", vc.theLabel.text)
		}
		return viewControllersList[index - 1]
		
	}
	
	func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
		
		guard let index = viewControllersList.firstIndex(of: viewController), index < viewControllersList.count - 1 else {
			return nil
		}
		if let vc = viewControllersList[index + 1] as? SomePageVC {
			print("viewControllerAfter:", vc.theLabel.text)
		}
		return viewControllersList[index + 1]

	}
	
	lazy var viewControllersList: [UIViewController] = []
	
	override func viewDidLoad() {
		super.viewDidLoad()
		
		self.dataSource = self
		self.delegate = self
		
		let colors: [UIColor] = [
			.red, .green, .systemBlue, .yellow, .cyan, .lightGray,
		]
		for i in 0..<6 {
			let vc = SomePageVC()
			vc.view.backgroundColor = colors[i % colors.count]
			vc.theLabel.text = "Page \(i)"
			viewControllersList.append(vc)
		}
		
		// if we have an odd number of "pages" we need to add a blank page at the end
		if viewControllersList.count % 2 == 1 {
			let vc = SomePageVC()
			vc.view.backgroundColor = .systemBackground
			vc.theLabel.text = "Blank"
			viewControllersList.append(vc)
		}
		
		if self.spineLocation == .mid {
			setViewControllers([viewControllersList[0], viewControllersList[1]], direction: .forward, animated: true)
		} else {
			setViewControllers([viewControllersList[0]], direction: .forward, animated: true)
		}
		
	}
	
	func pageViewController(_ pageViewController: UIPageViewController, spineLocationFor interfaceOrientation: UIInterfaceOrientation) -> UIPageViewController.SpineLocation {

		// safely unwrap optionals
		guard let curVC = pageViewController.viewControllers?.first, let idx = viewControllersList.firstIndex(of: curVC)
		else { fatalError("This should never happen!") }
		
		if interfaceOrientation.isLandscape {
			pageViewController.isDoubleSided = true
			let newIDX = (idx % 2 == 1) ? idx - 1 : idx
			setViewControllers([viewControllersList[newIDX], viewControllersList[newIDX + 1]], direction: .forward, animated: true, completion: nil)
		} else {
			pageViewController.isDoubleSided = false
			setViewControllers([viewControllersList[idx]], direction: .forward, animated: true, completion: nil)
		}
		
		return interfaceOrientation.isLandscape ? .mid : .min
		
	}
}

// 2. PageViewControllerRepresentable
struct MyViewControllerRepresentable: UIViewControllerRepresentable {
	
	func makeUIViewController(context: Context) -> CustomPageViewController {
		let pageViewController = CustomPageViewController(transitionStyle: .pageCurl, navigationOrientation: .horizontal)
		return pageViewController
	}
	
	func updateUIViewController(_ uiViewController: CustomPageViewController, context: Context) {
		// Update the UIPageViewController if needed
	}
	
}

struct TestView : View {
	var body: some View{
		VStack{
			MyViewControllerRepresentable()
		}
	}
}

#Preview {
    TestView()
}