simplex-chat/apps/ios/Shared/Views/ZoomableScrollView.swift

//
//  ZoomableScrollView.swift
//  SimpleX
//
//  Created by Evgeny on 13/05/2022.
//  Copyright © 2022 SimpleX Chat. All rights reserved.
//

import SwiftUI

struct ZoomableScrollView<Content: View>: UIViewRepresentable {
    private var content: Content

    init(@ViewBuilder content: () -> Content) {
        self.content = content()
    }

    func makeUIView(context: Context) -> UIScrollView {
        // set up the UIScrollView
        let scrollView = UIScrollView()
        scrollView.delegate = context.coordinator  // for viewForZooming(in:)
        scrollView.maximumZoomScale = 20
        scrollView.minimumZoomScale = 1
        scrollView.bouncesZoom = true
        scrollView.backgroundColor = .black
        scrollView.insetsLayoutMarginsFromSafeArea = false

        // create a UIHostingController to hold our SwiftUI content
        let hostedView = context.coordinator.hostingController.view!
        hostedView.translatesAutoresizingMaskIntoConstraints = true
        hostedView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        hostedView.frame = scrollView.bounds
        scrollView.addSubview(hostedView)

        return scrollView
    }

    func makeCoordinator() -> Coordinator {
        Coordinator(hostingController: UIHostingController(rootView: self.content))
    }

    func updateUIView(_ uiView: UIScrollView, context: Context) {
        // update the hosting controller's SwiftUI content
        context.coordinator.hostingController.rootView = self.content
        assert(context.coordinator.hostingController.view.superview == uiView)
    }

    // MARK: - Coordinator
    class Coordinator: NSObject, UIScrollViewDelegate {
        var hostingController: UIHostingController<Content>

        init(hostingController: UIHostingController<Content>) {
            self.hostingController = hostingController
        }

        func viewForZooming(in scrollView: UIScrollView) -> UIView? {
            hostingController.view
        }
    }
}

struct ZoomablePageView<Content: View>: UIViewRepresentable {
    private var content: Content

    init(@ViewBuilder content: () -> Content) {
        self.content = content()
    }

    func makeUIView(context: Context) -> UIScrollView {
        let scrollView = UIScrollView()
        scrollView.delegate = context.coordinator
        scrollView.maximumZoomScale = 5
        scrollView.minimumZoomScale = 1
        scrollView.bouncesZoom = true
        scrollView.backgroundColor = .clear

        let hostedView = context.coordinator.hostingController.view!
        hostedView.backgroundColor = .clear
        hostedView.translatesAutoresizingMaskIntoConstraints = false
        scrollView.addSubview(hostedView)
        NSLayoutConstraint.activate([
            hostedView.leadingAnchor.constraint(equalTo: scrollView.contentLayoutGuide.leadingAnchor),
            hostedView.trailingAnchor.constraint(equalTo: scrollView.contentLayoutGuide.trailingAnchor),
            hostedView.topAnchor.constraint(equalTo: scrollView.contentLayoutGuide.topAnchor),
            hostedView.bottomAnchor.constraint(equalTo: scrollView.contentLayoutGuide.bottomAnchor),
            hostedView.widthAnchor.constraint(equalTo: scrollView.frameLayoutGuide.widthAnchor)
        ])

        return scrollView
    }

    func makeCoordinator() -> Coordinator {
        Coordinator(hostingController: UIHostingController(rootView: self.content))
    }

    func updateUIView(_ uiView: UIScrollView, context: Context) {
        context.coordinator.hostingController.rootView = self.content
    }

    class Coordinator: NSObject, UIScrollViewDelegate {
        var hostingController: UIHostingController<Content>

        init(hostingController: UIHostingController<Content>) {
            self.hostingController = hostingController
        }

        func viewForZooming(in scrollView: UIScrollView) -> UIView? {
            hostingController.view
        }
    }
}