ParallaxHeaderView.swift

//
//  ParallaxHeaderView.swift
//
//  Created by nya on 2021/03/19.
//

import SwiftUI
import MXParallaxHeader

class ParallaxViewController: MXScrollViewController, MXScrollViewDelegate {
    
    var headerHeight: CGFloat = 0
    var headerMinimumHeight: CGFloat = 0
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        scrollView.parallaxHeader.minimumHeight = headerMinimumHeight
        scrollView.parallaxHeader.height = headerHeight
        scrollView.delegate = self
    }
    
    func updateHeaderHeight(animated: Bool = false) {
        let height = headerHeight
        
        if animated {
            UIView.animate(withDuration: 0.3) { [weak self] in
                self?.scrollView.parallaxHeader.height = height
            }
        } else {
            scrollView.parallaxHeader.height = height

            view.setNeedsLayout()
            UIView.performWithoutAnimation {
                view.layoutIfNeeded()
                scrollView.contentOffset.y = scrollView.contentInset.top - scrollView.adjustedContentInset.top
            }
        }
    }
}

class ParallaxViewControllerHeader: UIViewController {
    
    let controller: UIViewController
    var heightConstraint: NSLayoutConstraint?

    init(header: UIViewController) {
        controller = header
        super.init(nibName: nil, bundle: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.clipsToBounds = false

        addChild(controller)
        view.addSubview(controller.view)
        controller.didMove(toParent: self)
        
        let height = controller.view.systemLayoutSizeFitting(CGSize(width: UIScreen.main.bounds.width, height: .infinity)).height
        let heightConstraint = controller.view.heightAnchor.constraint(equalToConstant: height)
        
        controller.view.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            controller.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            controller.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            //controller.view.topAnchor.constraint(equalTo: view.topAnchor),
            controller.view.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            heightConstraint,
        ])
        self.heightConstraint = heightConstraint
    }
    
    func updateHeight(animated: Bool = false) -> CGFloat {
        heightConstraint?.isActive = false
        controller.view.setNeedsLayout()
        controller.view.layoutIfNeeded()
        let height = controller.view.systemLayoutSizeFitting(CGSize(width: UIScreen.main.bounds.width, height: .infinity)).height
        heightConstraint?.constant = height
        heightConstraint?.isActive = true

        if animated {
            UIView.animate(withDuration: 0.3) { [weak self] in
                self?.view.layoutIfNeeded()
            }
        }
        
        return height
    }
}

struct ParallaxHeaderView<Header: View, Content: View>: UIViewControllerRepresentable {
    
    @Binding var update: Bool
    let header: Header
    let content: Content
    
    init(update: Binding<Bool>, @ViewBuilder header: () -> Header, @ViewBuilder content: () -> Content) {
        self._update = update
        self.header = header()
        self.content = content()
    }
    
    func makeUIViewController(context: Context) -> ParallaxViewController {
        let vc = ParallaxViewController()
        vc.childViewController = UIViewController.hostingController {
            content
        }
        updateUIViewController(vc, context: context)
        return vc
    }

    func updateUIViewController(_ vc: ParallaxViewController, context: Context) {
        vc.headerViewController = ParallaxViewControllerHeader(header: UIViewController.hostingController {
            header
        })
        if let height = (vc.headerViewController as? ParallaxViewControllerHeader)?.updateHeight(animated: true) {
            vc.headerHeight = height
            vc.updateHeaderHeight(animated: true)
        }
    }
}

struct ParallaxHeaderPreview: View {
    
    @State var texts: [String] = [NSUUID().uuidString]
    @State var update: Bool = false

    var body: some View {
        ParallaxHeaderView(update: $update) {
            VStack {
                Text("Header")
                    .font(.system(size: 17, weight: .bold))
                    .padding(.vertical)
                ForEach(texts, id: \.self) {
                    Text($0)
                        .padding(.vertical)
                }
                HStack(spacing: 60) {
                    Button(action: {
                        if !texts.isEmpty {
                            texts.removeLast()
                            update.toggle()
                        }
                    }, label: {
                        Image(systemName: "minus")
                            .resizable()
                            .scaledToFit()
                            .frame(width: 30)
                            .frame(height: 30)
                    })
                    Button(action: {
                        texts.append(NSUUID().uuidString)
                        update.toggle()
                    }, label: {
                        Image(systemName: "plus")
                            .resizable()
                            .scaledToFit()
                            .frame(width: 30)
                            .frame(height: 30)
                    })
                }
                .padding()
            }
            .frame(maxWidth: .infinity)
            .background(Color.blue.opacity(0.5))
        } content: {
            VStack(spacing: 0) {
                HStack {
                    Text("Content")
                        .font(.system(size: 17, weight: .bold))
                        .padding(.vertical)
                }
                .frame(maxWidth: .infinity)
                .frame(height: 44)
                .background(Color.green.opacity(0.5))
                List {
                    ForEach(0 ..< 100) {
                        Text("\($0)")
                    }
                    .listRowBackground(Color.green)
                }
            }
        }
    }
}

struct ParallaxHeaderView_Previews: PreviewProvider {
    
    static var previews: some View {
        ParallaxHeaderPreview()
    }
}