my-files-sample/BeReal/Login/Views/LoginView.swift

//
//  LoginView.swift
//  BeReal
//
//  Created by Javier Cicchelli on 30/11/2022.
//  Copyright © 2022 Röck+Cöde. All rights reserved.
//

import SwiftUI

struct LoginView: View {
    
    // MARK: States

    @State private var topPadding: CGFloat = 0
    
    // MARK: Body
    
    var body: some View {
        ScrollView(
            .vertical,
            showsIndicators: false
        ) {
            Container()
                .padding(.horizontal, 24)
                .padding(.top, topPadding)
        }
        .background(Color.red)
        .ignoresSafeArea()
        .overlay(ViewHeightGeometry())
        .onPreferenceChange(ViewHeightPreferenceKey.self) { height in
            topPadding = height * 0.25
        }
    }
    
}

// MARK: - Views

fileprivate extension LoginView {
    struct Container: View {
        @State private var username: String = .empty
        @State private var password: String = .empty
        @State private var errorMessage: String?

        var body: some View {
            VStack(spacing: 24) {
                Text("My NFS")
                    .font(.largeTitle)
                    .fontWeight(.bold)
  
                LoginForm(
                    username: $username,
                    password: $password,
                    errorMessage: $errorMessage
                )

                Button {
                    // ...
                } label: {
                    Text("Log in")
                        .font(.body)
                        .fontWeight(.semibold)
                        .padding(.vertical, 8)
                        .padding(.horizontal, 32)
                        .background(
                            Capsule()
                                .foregroundColor(.white)
                        )
                }
            }
        }
    }
    
    struct ViewHeightGeometry: View {
        var body: some View {
            GeometryReader { proxy in
                Color.clear.preference(
                    key: ViewHeightPreferenceKey.self,
                    value: proxy.size.height + proxy.safeAreaInsets.top + proxy.safeAreaInsets.bottom
                )
            }
        }
    }
}

// MARK: - Preference keys

struct ViewHeightPreferenceKey: PreferenceKey {
    static var defaultValue: CGFloat = 0
    
    static func reduce(value: inout CGFloat, nextValue: () -> CGFloat) {
        value = nextValue()
    }
}

// MARK: - Previews

struct LoginView_Previews: PreviewProvider {
    static var previews: some View {
        LoginView()
    }
}