frenzy-ios/Reader/Screens/AppNavigationController.swift

//
//  AppNavigationController.swift
//  Reader
//
//  Created by Shadowfacts on 1/10/22.
//

import UIKit

class AppNavigationController: UINavigationController, UINavigationControllerDelegate {
    
    private var statusBarBlockingView: UIView!

    override func viewDidLoad() {
        super.viewDidLoad()
        
        let appearance = UINavigationBarAppearance()
        appearance.configureWithOpaqueBackground()
        navigationBar.scrollEdgeAppearance = appearance

        interactivePopGestureRecognizer?.isEnabled = false
        let recognizer = UIPanGestureRecognizer(target: self, action: #selector(panGestureRecognized))
        recognizer.allowedScrollTypesMask = .continuous
        view.addGestureRecognizer(recognizer)
        
        isNavigationBarHidden = true
        
        statusBarBlockingView = UIVisualEffectView(effect: UIBlurEffect(style: .regular))
        statusBarBlockingView.translatesAutoresizingMaskIntoConstraints = false
        statusBarBlockingView.layer.zPosition = 101
        view.addSubview(statusBarBlockingView)
        
        NSLayoutConstraint.activate([
            statusBarBlockingView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            statusBarBlockingView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            statusBarBlockingView.topAnchor.constraint(equalTo: view.topAnchor),
            statusBarBlockingView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
        ])
        
        delegate = self
    }
    
    func navigationController(_ navigationController: UINavigationController, willShow viewController: UIViewController, animated: Bool) {
        statusBarBlockingView.isHidden = viewController.prefersStatusBarHidden
    }
    
    private var poppingViewController: UIViewController?
    private var prevNavBarHidden = false
    private var dimmingView: UIView = {
        let v = UIView()
        v.backgroundColor = .black
        return v
    }()
    
    @objc private func panGestureRecognized(_ recognizer: UIPanGestureRecognizer) {
        let translation = recognizer.translation(in: view)
        let translationProgress = max(0, translation.x) / view.bounds.width
        
        switch recognizer.state {
        case .began:
            guard viewControllers.count > 1 else {
                break
            }
            prevNavBarHidden = isNavigationBarHidden
            poppingViewController = popViewController(animated: false)
            view.addSubview(poppingViewController!.view)
            poppingViewController!.view.transform = CGAffineTransform(translationX: max(0, translation.x), y: 0)
            poppingViewController!.view.layer.zPosition = 100
            dimmingView.frame = view.bounds
            dimmingView.layer.opacity = Float(1 - translationProgress) * 0.075
            dimmingView.layer.zPosition = 99
            view.addSubview(dimmingView)
            // changing the transform directly on topViewController.view doesn't work for some reason, have to go 2 superviews up
            topViewController!.view.superview?.superview?.transform = CGAffineTransform(translationX: (1 - translationProgress) * -0.3 * view.bounds.width, y: 0)
            
        case .changed:
            guard let poppingViewController = poppingViewController else {
                break
            }

            poppingViewController.view.transform = CGAffineTransform(translationX: max(0, translation.x), y: 0)
            dimmingView.layer.opacity = Float(1 - max(0, translation.x) / view.bounds.width) * 0.075
            topViewController!.view.superview?.superview?.transform = CGAffineTransform(translationX: (1 - translationProgress) * -0.3 * view.bounds.width, y: 0)
            
        case .ended:
            guard let poppingViewController = poppingViewController else {
                break
            }
            
            let velocity = recognizer.velocity(in: view)
            let shouldComplete = translation.x >= view.bounds.width / 2 || velocity.x >= 500
            
            UIView.animate(withDuration: 0.2, delay: 0, options: .curveEaseInOut) {
                if shouldComplete {
                    poppingViewController.view.transform = CGAffineTransform(translationX: self.view.bounds.width, y: 0)
                    self.topViewController!.view.superview?.superview?.transform = .identity
                } else {
                    poppingViewController.view.transform = .identity
                    self.topViewController!.view.superview?.superview?.transform = CGAffineTransform(translationX: -0.3 * self.view.bounds.width, y: 0)
                }
                self.dimmingView.layer.opacity = 0
            } completion: { _ in
                self.topViewController!.view.superview?.superview?.transform = .identity
                
                if shouldComplete {
                    poppingViewController.beginAppearanceTransition(false, animated: true)
                    poppingViewController.willMove(toParent: nil)
                    poppingViewController.removeFromParent()
                    poppingViewController.view.removeFromSuperview()
                    poppingViewController.endAppearanceTransition()
                } else {
                    self.pushViewController(poppingViewController, animated: false)
                    self.isNavigationBarHidden = self.prevNavBarHidden
                }
                
                poppingViewController.view.layer.zPosition = 0
                self.poppingViewController = nil
                self.dimmingView.removeFromSuperview()
            }

        default:
            break
        }
    }

}