View+Extension.swift

//Original code from https://github.com/SwiftUIX/SwiftUIX by @vmanot

import Foundation
import SwiftUI
import UIKit

extension View {
    @inlinable
    public func navigationBarItems<Leading: View, Center: View, Trailing: View>(
        leading: Leading,
        center: Center,
        trailing: Trailing,
        displayMode: NavigationBarItem.TitleDisplayMode? = .automatic
    ) -> some View {
        background(NavigationBarConfigurator(leading: leading, center: center, trailing: trailing, displayMode: displayMode))
    }
    
    @inlinable
    public func navigationBarItems<Leading: View, Center: View>(
        leading: Leading,
        center: Center,
        displayMode: NavigationBarItem.TitleDisplayMode = .automatic
    ) -> some View {
        navigationBarItems(leading: leading, center: center, trailing: EmptyView(), displayMode: displayMode)
    }
    
    @inlinable
    public func navigationBarTitleView<V: View>(
        _ center: V,
        displayMode: NavigationBarItem.TitleDisplayMode
    ) -> some View {
        navigationBarItems(leading: EmptyView(), center: center, trailing: EmptyView(), displayMode: displayMode)
    }
    
    @inlinable
    public func navigationBarTitleView<V: View>(
        _ center: V
    ) -> some View {
        navigationBarItems(leading: EmptyView(), center: center, trailing: EmptyView(), displayMode: .automatic)
    }

    @inlinable
    public func navigationBarItems<Center: View, Trailing: View>(
        center: Center,
        trailing: Trailing,
        displayMode: NavigationBarItem.TitleDisplayMode = .automatic
    ) -> some View {
        navigationBarItems(leading: EmptyView(), center: center, trailing: trailing, displayMode: displayMode)
    }
}

@usableFromInline
struct NavigationBarConfigurator<Leading: View, Center: View, Trailing: View>: UIViewControllerRepresentable {
    @usableFromInline
    class UIViewControllerType: UIViewController {
        var leading: Leading? {
            didSet {
                updateNavigationBar(parent: parent)
            }
        }
        
        var center: Center? {
            didSet {
                updateNavigationBar(parent: parent)
            }
        }
        
        var trailing: Trailing? {
            didSet {
                updateNavigationBar(parent: parent)
            }
        }
        
        var displayMode: NavigationBarItem.TitleDisplayMode? {
            didSet {
                updateNavigationBar(parent: parent)
            }
        }
                
        override func willMove(toParent parent: UIViewController?) {
            updateNavigationBar(parent: parent)
            
            super.willMove(toParent: parent)
        }
        
        private func updateNavigationBar(parent: UIViewController?) {
            guard let parent = parent else {
                return
            }
            
            #if os(iOS) || targetEnvironment(macCatalyst)
            if let displayMode = displayMode {
                switch displayMode {
                    case .automatic:
                        parent.navigationItem.largeTitleDisplayMode = .automatic
                    case .inline:
                        parent.navigationItem.largeTitleDisplayMode = .never
                    case .large:
                        parent.navigationItem.largeTitleDisplayMode = .always
                    @unknown default:
                        parent.navigationItem.largeTitleDisplayMode = .automatic
                }
            }
            #endif
            
            if let leading = leading {
                if !(leading is EmptyView) {
                    if parent.navigationItem.leftBarButtonItem == nil {
                        parent.navigationItem.leftBarButtonItem = .init(customView: UIHostingView(rootView: leading))
                    } else if let view = parent.navigationItem.leftBarButtonItem?.customView as? UIHostingView<Leading> {
                        view.rootView = leading
                    } else {
                        parent.navigationItem.leftBarButtonItem?.customView = UIHostingView(rootView: leading)
                    }
                }
            } else {
                parent.navigationItem.leftBarButtonItem = nil
            }
            
            if let center = center {
                if !(center is EmptyView) {
                    if let view = parent.navigationItem.titleView as? UIHostingView<Center> {
                        view.rootView = center
                    } else {
                        parent.navigationItem.titleView = UIHostingView(rootView: center)
                    }
                }
            } else {
                parent.navigationItem.titleView = nil
            }
            
            if let trailing = trailing {
                if !(trailing is EmptyView) {
                    if parent.navigationItem.rightBarButtonItem == nil {
                        parent.navigationItem.rightBarButtonItem = .init(customView: UIHostingView(rootView: trailing))
                    } else if let view = parent.navigationItem.rightBarButtonItem?.customView as? UIHostingView<Trailing> {
                        view.rootView = trailing
                    } else {
                        parent.navigationItem.rightBarButtonItem?.customView = UIHostingView(rootView: trailing)
                    }
                }
            } else {
                parent.navigationItem.rightBarButtonItem = nil
            }
            
            parent.navigationItem.leftBarButtonItem?.customView?.sizeToFit()
            parent.navigationItem.titleView?.sizeToFit()
            parent.navigationItem.rightBarButtonItem?.customView?.sizeToFit()
        }
    }
    
    let leading: Leading
    let center: Center
    let trailing: Trailing
    let displayMode: NavigationBarItem.TitleDisplayMode?
    
    @usableFromInline
    init(
        leading: Leading,
        center: Center,
        trailing: Trailing,
        displayMode: NavigationBarItem.TitleDisplayMode?
    ) {
        self.leading = leading
        self.center = center
        self.trailing = trailing
        self.displayMode = displayMode
    }
    
    @usableFromInline
    func makeUIViewController(context: Context) -> UIViewControllerType {
        .init()
    }
    
    @usableFromInline
    func updateUIViewController(_ viewController: UIViewControllerType, context: Context) {
        viewController.displayMode = displayMode
        viewController.leading = leading
        viewController.center = center
        viewController.trailing = trailing
    }
}


/// A `UIView` subclass capable of hosting a SwiftUI view.
open class UIHostingView<Content: View>: UIView {
    private let rootViewHostingController: UIHostingController<Content>
    
    public var rootView: Content {
        get {
            return rootViewHostingController.rootView
        } set {
            rootViewHostingController.rootView = newValue
        }
    }
    
    public required init(rootView: Content) {
        self.rootViewHostingController = UIHostingController(rootView: rootView)
        
        super.init(frame: .zero)
        
        rootViewHostingController.view.backgroundColor = .clear
        
        addSubview(rootViewHostingController.view)
    }
    
    public required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override open func sizeThatFits(_ size: CGSize) -> CGSize {
        rootViewHostingController.sizeThatFits(in: size)
    }
    
    override open func systemLayoutSizeFitting(_ targetSize: CGSize) -> CGSize {
        rootViewHostingController.sizeThatFits(in: targetSize)
    }
    
    override open func systemLayoutSizeFitting(
        _ targetSize: CGSize,
        withHorizontalFittingPriority horizontalFittingPriority: UILayoutPriority,
        verticalFittingPriority: UILayoutPriority
    ) -> CGSize {
        rootViewHostingController.sizeThatFits(in: targetSize)
    }
    
    override open func layoutSubviews() {
        super.layoutSubviews()
        
        rootViewHostingController.view.frame = bounds
    }
    
    override open func sizeToFit() {
        if let superview = superview {
            frame.size = rootViewHostingController.sizeThatFits(in: superview.frame.size)
        } else {
            super.sizeToFit()
        }
    }
}