ParentWidtReader.swift

/* Using GeometryReader to find out the width of the parent is problematic when the parent does not have a height and depends on its children to give it height, e.g. VStack, ScrollView, etc GeometryReader takes up all the space it can get but if the parent has no height then GeometryReader will simply not have a height and your view will not render properly. ParentWidthReader uses a widely used workaround using PreferenceKey and a GeometryReader as a background thus bypassing the height problem.
*/
import SwiftUI

struct ParentWidthReader<Content>: View where Content: View {
    typealias ContentBuilder = (CGFloat) -> Content
    
    @State var width: CGFloat = .infinity
    let content: ContentBuilder
    
    init(@ViewBuilder content: @escaping ContentBuilder) {        
        self.content = content
    }
    
    var body: some View {
        content(width)
        EmptyView()
        .frame(maxWidth: .infinity)
        .background(
            GeometryReader {
                Color.clear
                    .preference(key: ViewWidthKey.self, value: $0.frame(in: .local).size.width)
            }
        )
        .onPreferenceChange(ViewWidthKey.self) { value in
            self.width = value
        }
    }
}

private struct ViewWidthKey: PreferenceKey {
    typealias Value = CGFloat
    static var defaultValue = CGFloat.zero
    static func reduce(value: inout Value, nextValue: () -> Value) {
        value += nextValue()
    }
}