import SwiftUI

//自作パッケージの切り出しなので変数名がめちゃくちゃです
//詳しくはこれの実装を見てください　https://github.com/Chronos2500/CustomNavigationTitle

struct ContentView: View {
    var body: some View {
        NavigationStack{
            ScrollView {
                Color.blue.frame(height: 200)
                    .titleVisibilityAnchor()
                Text("サンプルページ")
                    .frame(maxWidth: .infinity,alignment: .center)
            }
            .scrollAwareTitle()
        }
    }
}

struct BoundsPreferenceKey: PreferenceKey {
    typealias Value = Anchor<CGRect>?
    static let defaultValue: Value = nil
    static func reduce(value: inout Value, nextValue: () -> Value) {
        guard let newValue = nextValue() else { return }
        value = newValue
    }
}

extension View {
    public func titleVisibilityAnchor() -> some View {
        self.anchorPreference(
            key: BoundsPreferenceKey.self,
            value: .bounds
        ) { anchor in
            anchor
        }
    }
}

private struct ScrollAwareTitleModifier: ViewModifier {
    @State var isShowNavigationTitle = false
    func body(content: Content) -> some View {
        content
            .backgroundPreferenceValue(BoundsPreferenceKey.self) { anchor in
                GeometryReader { proxy in
                    if let anchor = anchor {
                        let scrollFrame = proxy.frame(in: .local).minY
                        let itemFrame = proxy[anchor]
                        let isVisible = (itemFrame.maxY + 22) > scrollFrame
                        DispatchQueue.main.async{
                            if isVisible {
                                isShowNavigationTitle = false
                            } else if !isVisible {
                                isShowNavigationTitle = true
                            }
                        }
                    }
                    return Color.clear
                }
            }
            .toolbarBackgroundVisibility(.hidden, for: .navigationBar)
            .toolbar {
                ToolbarItem(placement: .topBarTrailing) {
                    Image(systemName: "xmark.circle.fill")
                        .imageScale(.large)
                        .foregroundStyle(isShowNavigationTitle ? .blue : .red)
                        .animation(.easeIn(duration: 0.15), value: isShowNavigationTitle)
                }
            }
    }
}

extension View {
    public func scrollAwareTitle() -> some View {
        modifier(ScrollAwareTitleModifier())
    }
}