Gemini/Gemini-iOS/BrowserNavigationController.swift

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

import UIKit
import BrowserCore
import Combine
import SwiftUI

class BrowserNavigationController: UIViewController {

    let navigator: NavigationManager
    
    private var backBrowserVCs = [BrowserWebViewController]()
    private var forwardBrowserVCs = [BrowserWebViewController]()
    private var currentBrowserVC: BrowserWebViewController!
    
    private var browserContainer: UIView!
    private var toolbarView: ToolbarView!
    
    private var gestureState: GestureState?
    private var trackingScroll = false
    private var prevScrollViewContentOffset: CGPoint?
    private var toolbarOffset: CGFloat = 0 {
        didSet {
            toolbarView.transform = CGAffineTransform(translationX: 0, y: toolbarOffset)
        }
    }
    
    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
        
        browserContainer = UIView()
        browserContainer.translatesAutoresizingMaskIntoConstraints = false
        view.embedSubview(browserContainer)
        
        currentBrowserVC = createBrowserVC(url: navigator.currentURL)
        currentBrowserVC.scrollViewDelegate = self
        embedChild(currentBrowserVC, in: browserContainer)
        
        toolbarView = ToolbarView(navigator: navigator)
        toolbarView.showShareSheet = self.showShareSheet
        toolbarView.showPreferences = self.showPreferences
        toolbarView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(toolbarView)
        NSLayoutConstraint.activate([
            toolbarView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            toolbarView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            toolbarView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
        ])
        
        navigator.navigationOperation
            .sink(receiveValue: self.onNavigate)
            .store(in: &cancellables)
        
        view.addGestureRecognizer(UIPanGestureRecognizer(target: self, action: #selector(panGestureRecognized)))
    }
    
    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        
        setBrowserVCSafeAreaInsets(currentBrowserVC)
    }
    
    private func createBrowserVC(url: URL) -> BrowserWebViewController {
        let vc = BrowserWebViewController(navigator: navigator, url: url)
        setBrowserVCSafeAreaInsets(vc)
        return vc
    }
    
    private func setBrowserVCSafeAreaInsets(_ vc: BrowserWebViewController) {
        guard let toolbarView = toolbarView else { return }
        vc.additionalSafeAreaInsets = UIEdgeInsets(top: 0, left: 0, bottom: toolbarView.bounds.height - view.safeAreaInsets.bottom - toolbarOffset, right: 0)
    }
    
    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.scrollViewDelegate = nil
        currentBrowserVC = newVC
        currentBrowserVC.scrollViewDelegate = self
        embedChild(newVC, in: browserContainer)
    }
    
    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, in: browserContainer)
                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
                browserContainer.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.goBack()
                    }
                }
                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, in: browserContainer)
                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
                browserContainer.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.goForward()
                    }
                }
                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
        }
    }
    
    private func showShareSheet(_ source: UIView) {
        let vc = UIActivityViewController(activityItems: [navigator.currentURL], applicationActivities: nil)
        vc.popoverPresentationController?.sourceView = source
        present(vc, animated: true)
    }
    
    private func showPreferences() {
        let host = UIHostingController(rootView: PreferencesView())
        present(host, animated: true)
    }

}

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

extension BrowserNavigationController: UIScrollViewDelegate {
    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
        trackingScroll = true
        prevScrollViewContentOffset = scrollView.contentOffset
    }

    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        guard trackingScroll else { return }
        defer { prevScrollViewContentOffset = scrollView.contentOffset }
        guard let prevOffset = prevScrollViewContentOffset else { return }
        
        let delta = scrollView.contentOffset.y - prevOffset.y
        
        let belowEnd = scrollView.contentOffset.y > scrollView.contentSize.height - scrollView.bounds.height + scrollView.safeAreaInsets.bottom
        
        if belowEnd {
            UIView.animate(withDuration: 0.15, delay: 0, options: .curveEaseInOut) {
                self.toolbarOffset = 0
            } completion: { (_) in
                self.setBrowserVCSafeAreaInsets(self.currentBrowserVC)
            }
            trackingScroll = false
        } else if delta > 0 || (delta < 0 && toolbarOffset < toolbarView.bounds.height) {
            toolbarOffset = max(0, min(toolbarView.bounds.height, toolbarOffset + delta))
            
            setBrowserVCSafeAreaInsets(currentBrowserVC)
        }
    }
    
    func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
        guard trackingScroll else { return }
        trackingScroll = false
        
        let finalOffset: CGFloat
        if velocity.y < 0 {
            finalOffset = 0
        } else {
            finalOffset = toolbarView.bounds.height
        }
        
        UIView.animate(withDuration: 0.15, delay: 0, options: .curveEaseOut) {
            self.toolbarOffset = finalOffset
        }
    }
}