Custom picker using style via environment

CustomPicker.swift

import SwiftUI

struct ContentView: View {
    @State private var selection: Int = 0

    var body: some View {
        CustomPicker(selection: $selection) {
//            ForEach(0..<10) {
//                Text("\($0)")
//            }
            Text("First").tag(0)
            Text("Second").tag(1)
            VStack {
                Image(systemName: "paperplane")
                Text("Third")
            }.tag(2)
            Text("Fourth").tag(3)
        }
    }
}

protocol CustomPickerStyle {
    func makeBody<SelectionValue: Hashable, Content: View>(selection: Binding<SelectionValue>, content: Content) -> AnyView
}

struct CustomPickerStyleEnvironmentKey: EnvironmentKey {
    static var defaultValue: CustomPickerStyle = HorizontalCustomPickerStyle()
}

extension EnvironmentValues {
    var customPickerStyle: CustomPickerStyle {
        get { self[CustomPickerStyleEnvironmentKey.self] }
        set { self[CustomPickerStyleEnvironmentKey.self] = newValue }
    }
}

extension View {
    func customPickerStyle<S: CustomPickerStyle>(_ style: S) -> some View {
        environment(\.customPickerStyle, style)
    }
}

extension View {
    func findTag<T: Hashable>() -> T? {
        if self is AnyView {
            if let content = Mirror(reflecting: self).descendant("storage", "view") {
                let tag = Mirror(reflecting: content).descendant("modifier", "value", "tagged")
                if let tag = tag as? T {
                    return tag
                } else {
                    return nil
                }
            } else {
                return nil
            }
        } else {
            return Mirror(reflecting: self).descendant("modifier", "value", "tagged") as? T
        }
    }
}

struct HorizontalCustomPickerStyle: CustomPickerStyle {
    func makeBody<SelectionValue: Hashable, Content: View>(selection: Binding<SelectionValue>, content: Content) -> AnyView {
        AnyView(LinearPicker(selection: selection, content: content))
    }
}

struct LinearPicker<SelectionValue: Hashable, Content: View>: View {
    @Namespace var ns
    @Binding var selection: SelectionValue
    let content: Content

    @ViewBuilder
    var body: some View {
        let contentMirror = Mirror(reflecting: content)
        if let contentDescendant = contentMirror.descendant("value") {
            let blocksCount = Mirror(reflecting: contentDescendant).children.count
            HStack {
                ForEach(0..<blocksCount) { index in
                    if let value = contentMirror.descendant("value", ".\(index)"), let tupleBlock = AnyView(_fromValue: value), let tag: SelectionValue = tupleBlock.findTag() {
                        cell(for: tag, using: tupleBlock)
                    }
                }
            }
        } else if let tag: SelectionValue = content.findTag() {
            cell(for: tag, using: AnyView(content))
        } else {
            // TODO ForEach case
            EmptyView()
        }
    }

    private func cell(for tag: SelectionValue, using content: AnyView) -> some View {
        Button {
            selection = tag
        } label: {
            content
                .padding(.vertical, 16)
        }
        .background(
            Group {
                if tag == selection {
                    Color.purple.frame(height: 2)
                        .matchedGeometryEffect(id: "selector", in: ns)
                }
            },
            alignment: .bottom
        )
        .accentColor(tag == selection ? .purple : .black)
        .animation(.easeInOut)
    }
}

struct CustomPicker<SelectionValue, Content>: View where SelectionValue: Hashable, Content: View {
    @Environment(\.customPickerStyle) private var style
    @Binding var selection: SelectionValue
    let content: Content

    init(selection: Binding<SelectionValue>, @ViewBuilder content: () -> Content) {
        self._selection = selection
        self.content = content()
    }

    var body: some View {
        style.makeBody(selection: $selection, content: content)
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}