Gemini/Gemini-iOS/BrowserNavigationController.swift

//
//  BrowserNavigationController.swift
//  Gemini-iOS
//
//  Created by Shadowfacts on 12/17/20.
//

import UIKit
import BrowserCore
import Combine

class BrowserNavigationController: UIViewController {

    let navigator: NavigationManager
    
    private var backBrowserVCs = [BrowserWebViewController]()
    private var forwardBrowserVCs = [BrowserWebViewController]()
    private var currentBrowserVC: BrowserWebViewController!
    
    private var gestureState: GestureState?
    
    private var cancellables = [AnyCancellable]()
    
    init(navigator: NavigationManager) {
        self.navigator = navigator
        
        super.init(nibName: nil, bundle: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = .systemBackground
        
        currentBrowserVC = BrowserWebViewController(navigator: navigator, url: navigator.currentURL)
        embedChild(currentBrowserVC)
        
        navigator.navigationOperation
            .sink(receiveValue: self.onNavigate)
            .store(in: &cancellables)
        
        view.addGestureRecognizer(UIPanGestureRecognizer(target: self, action: #selector(panGestureRecognized)))
    }
    
    private func onNavigate(_ operation: NavigationManager.Operation) {
        let newVC: BrowserWebViewController
        
        switch operation {
        case .go:
            backBrowserVCs.append(currentBrowserVC)
            newVC = BrowserWebViewController(navigator: navigator, url: navigator.currentURL)
            
        case let .backward(count: count):
            var removed = backBrowserVCs.suffix(count)
            backBrowserVCs.removeLast(count)
            forwardBrowserVCs.insert(currentBrowserVC, at: 0)
            newVC = removed.removeFirst()
            forwardBrowserVCs.insert(contentsOf: removed, at: 0)
            
        case let .forward(count: count):
            var removed = forwardBrowserVCs.prefix(count)
            forwardBrowserVCs.removeFirst(count)
            backBrowserVCs.append(currentBrowserVC)
            newVC = removed.removeFirst()
            backBrowserVCs.append(contentsOf: removed)
        }
        
        currentBrowserVC.removeViewAndController()
        currentBrowserVC = newVC
        embedChild(newVC)
    }
    
    private let startEdgeNavigationSwipeDistance: CGFloat = 75
    private let finishEdgeNavigationVelocityThreshold: CGFloat = 500
    private let edgeNavigationMaxDimmingAlpha: CGFloat = 0.35
    private let edgeNavigationParallaxFactor: CGFloat = 0.25
    private let totalEdgeNavigationTime: TimeInterval = 0.4
    
    @objc private func panGestureRecognized(_ recognizer: UIPanGestureRecognizer) {
        let location = recognizer.location(in: view)
        let velocity = recognizer.velocity(in: view)
        
        switch recognizer.state {
        case .began:
            if location.x < startEdgeNavigationSwipeDistance && velocity.x > 0 && navigator.backStack.count > 0 {
                let older = backBrowserVCs.last ?? BrowserWebViewController(navigator: navigator, url: navigator.backStack.last!)
                embedChild(older)
                older.view.layer.zPosition = -2
                older.view.transform = CGAffineTransform(translationX: -1 * edgeNavigationParallaxFactor * view.bounds.width, y: 0)
                
                let dimmingView = UIView()
                dimmingView.translatesAutoresizingMaskIntoConstraints = false
                dimmingView.backgroundColor = .black
                dimmingView.layer.zPosition = -1
                dimmingView.alpha = edgeNavigationMaxDimmingAlpha
                view.embedSubview(dimmingView)
                let animator = UIViewPropertyAnimator(duration: totalEdgeNavigationTime, curve: .easeInOut) {
                    dimmingView.alpha = 0
                    older.view.transform = .identity
                    self.currentBrowserVC.view.transform = CGAffineTransform(translationX: self.view.bounds.width, y: 0)
                }
                animator.addCompletion { (position) in
                    dimmingView.removeFromSuperview()
                    
                    older.view.transform = .identity
                    older.view.layer.zPosition = 0
                    older.removeViewAndController()
                    
                    self.currentBrowserVC.view.transform = .identity
                    
                    if position == .end {
                        self.navigator.back()
                    }
                }
                gestureState = .backwards(animator)
            } else if location.x > view.bounds.width - startEdgeNavigationSwipeDistance && velocity.x < 0 && navigator.forwardStack.count > 0 {
                let newer = forwardBrowserVCs.first ?? BrowserWebViewController(navigator: navigator, url: navigator.backStack.first!)
                embedChild(newer)
                newer.view.transform = CGAffineTransform(translationX: view.bounds.width, y: 0)
                newer.view.layer.zPosition = 2
                
                let dimmingView = UIView()
                dimmingView.translatesAutoresizingMaskIntoConstraints = false
                dimmingView.backgroundColor = .black
                dimmingView.layer.zPosition = 1
                dimmingView.alpha = 0
                view.embedSubview(dimmingView)
                let animator = UIViewPropertyAnimator(duration: totalEdgeNavigationTime, curve: .easeInOut) {
                    dimmingView.alpha = self.edgeNavigationMaxDimmingAlpha
                    newer.view.transform = .identity
                    self.currentBrowserVC.view.transform = CGAffineTransform(translationX: -1 * self.edgeNavigationParallaxFactor * self.view.bounds.width, y: 0)
                }
                animator.addCompletion { (position) in
                    dimmingView.removeFromSuperview()
                    
                    newer.removeViewAndController()
                    newer.view.layer.zPosition = 0
                    newer.view.transform = .identity
                    
                    self.currentBrowserVC.view.transform = .identity
                    
                    if position == .end {
                        self.navigator.forward()
                    }
                }
                gestureState = .forwards(animator)
            }
        
        case .changed:
            let translation = recognizer.translation(in: view)
            
            switch gestureState {
            case let .backwards(animator):
                animator.fractionComplete = translation.x / view.bounds.width
            case let .forwards(animator):
                animator.fractionComplete = abs(translation.x) / view.bounds.width
            case nil:
                break
            }
            
        case .ended, .cancelled:
            switch gestureState {
            case let .backwards(animator):
                let shouldComplete = location.x > view.bounds.width / 2 || velocity.x > finishEdgeNavigationVelocityThreshold
                animator.isReversed = !shouldComplete
                animator.startAnimation()
            case let .forwards(animator):
                let shouldComplete = location.x < view.bounds.width / 2 || velocity.x < -finishEdgeNavigationVelocityThreshold
                animator.isReversed = !shouldComplete
                animator.startAnimation()
            case nil:
                break
            }
            
            gestureState = nil
            
        default:
            return
        }
    }

}

extension BrowserNavigationController {
    enum GestureState {
        case backwards(UIViewPropertyAnimator)
        case forwards(UIViewPropertyAnimator)
    }
}