SwiftUI - Flexible Navigation with Coordinators

MainView.swift

//
//  MainView.swift
//  SwiftUI Avoid Navigation Hardcoded
//
//  Created by Yannick Rave on 07.05.20.
//  Copyright © 2020 Rave. All rights reserved.
//

import SwiftUI

struct ItalicTextView: View {
    var text: String

    var body: some View {
        Text(text)
            .italic()
    }
}

struct BoldTextView: View {
    var text: String

    var body: some View {
        Text(text)
            .bold()
    }
}

struct ItalicTextViewCoordinator {
    var text: String
    
    func createView() -> ItalicTextView {
        return ItalicTextView(text: text)
    }
}

struct BoldTextViewCoordinator {
    var text: String
    
    func createView() -> BoldTextView {
        return BoldTextView(text: text)
    }
}

// Not reusable if you want to change the destination
struct NotReusableTextView: View {
    var text: String

    var body: some View {
        VStack {
            Text(text)
            NavigationLink("Link", destination: BoldTextView(text: text))
        }
    }
}

// A lot of nested code and dependencies
struct NestedMainView: View {
    @State var text: String

    var body: some View {
        ReusableNavigationLinkTextView(
            text: self.text,
            destination: {
                ReusableNavigationLinkTextView(
                    text: self.text,
                    destination: {
                        BoldTextView(text: self.text)
                    }
                )
            }
        )
    }
}


protocol ReusableNavigationLinkTextViewCoordinator {
    associatedtype Destination: View
    var destination: () -> Destination { get }

    func createView() -> ReusableNavigationLinkTextView<Destination>
}

struct ReusableNavigationLinkShowBoldViewCoordinator: ReusableNavigationLinkTextViewCoordinator {
    @Binding var text: String

    var destination: () -> BoldTextView {
        { return BoldTextView(text: self.text) }
    }

    func createView() -> ReusableNavigationLinkTextView<Destination> {
        return ReusableNavigationLinkTextView(text: self.text, destination: self.destination)
    }
}

struct ReusableNavigationLinkShowItalicViewCoordinator: ReusableNavigationLinkTextViewCoordinator {
    @Binding var text: String

    var destination: () -> ItalicTextView {
        { return ItalicTextView(text: self.text) }
    }

    func createView() -> ReusableNavigationLinkTextView<Destination> {
        return ReusableNavigationLinkTextView(text: self.text, destination: self.destination)
    }
}

struct ShowNavigationLinkUntilNumberGreaterFourThenItalicViewCoordinator: ReusableNavigationLinkTextViewCoordinator {
    @Binding var text: String
    let number: Int
    private var isNumberGreaterThan4: Bool {
        return number > 4
    }

    var destination: () -> AnyView {
        {
            if self.isNumberGreaterThan4 {
                let coordinator = ItalicTextViewCoordinator(text: self.text)
                return AnyView(
                    coordinator.createView()
                )
            } else {
                let coordinator = ShowNavigationLinkUntilNumberGreaterFourThenItalicViewCoordinator(
                    text: self.$text,
                    number: self.number + 1
                )
                return AnyView(coordinator.createView())
            }
        }
    }

    func createView() -> ReusableNavigationLinkTextView<AnyView> {
        return ReusableNavigationLinkTextView(text: self.text, destination: self.destination)
    }
}

struct ReusableNavigationLinkTextView<Destination: View>: View {
    var text: String
    var destination: () -> Destination

    var body: some View {
        VStack {
            Text(text)

            NavigationLink("Link", destination: self.destination())
        }
    }
}

struct MainView: View {
    @State var text = "Main"

    var body: some View {
        NavigationView {
            VStack(spacing: 32) {
                NavigationLink("Bold", destination: self.reuseThenBoldChild())
                NavigationLink("Reuse then Italic", destination: self.reuseThenItalicChild())
                NavigationLink("Greater Four", destination: self.numberGreaterFourChild())
                NavigationLink("Text Field", destination: self.textField())
            }
        }
    }

    func reuseThenBoldChild() -> some View {
        let coordinator = ReusableNavigationLinkShowBoldViewCoordinator(text: self.$text)
        return coordinator.createView()
    }

    func reuseThenItalicChild() -> some View {
        let coordinator = ReusableNavigationLinkShowItalicViewCoordinator(text: self.$text)
        return coordinator.createView()
    }

    func numberGreaterFourChild() -> some View {
        let coordinator = ShowNavigationLinkUntilNumberGreaterFourThenItalicViewCoordinator(text: self.$text, number: 1)
        return coordinator.createView()
    }

    func textField() -> some View {
        let coordinator = TextFieldEmptyReusableViewCoordinator(text: self.$text)
        return coordinator.createView()
    }
}

struct BoldNavigationLink: View {
    let text = "Text"
    var body: some View {
        ReusableNavigationLinkTextView(
            text: self.text,
            destination: { BoldTextView(text: self.text) }
        )
    }
}

struct TextFieldEmptyReusableViewCoordinator {
    @Binding var text: String

    func createView() -> some View {
        let reusableViewBoldCoordinator = ReusableNavigationLinkShowBoldViewCoordinator(text: self.$text)
        let reusableView = reusableViewBoldCoordinator.createView()

        let emptyView = EmptyNavigationLinkView(destination: { reusableView })

        let textField = TextFieldView(text: self.$text, destination: { emptyView })

        return textField
    }
}

struct TextFieldView<Destination: View>: View {
    @Binding var text: String
    var destination: () -> Destination

    var body: some View {
        VStack {
            TextField("Text", text: self.$text)

            NavigationLink("Next", destination: self.destination())
        }
    }
}

struct EmptyNavigationLinkView<Destination: View>: View {
    var destination: () -> Destination

    var body: some View {
        NavigationLink("Next", destination: self.destination())
    }
}

struct MainView_Previews: PreviewProvider {
    static var previews: some View {
        MainView()
    }
}