my-files-sample/Modules/Sources/Login/UI/Views/LoginView.swift

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

import APIService
import DataModels
import SwiftUI
import UseCases

public struct LoginView: View {
    
    // MARK: States

    @State private var containerTopPadding: CGFloat = 0
    
    // MARK: Properties
    
    private let authenticated: AuthenticatedClosure
    
    // MARK: Initialisers
    
    public init(authenticated: @escaping AuthenticatedClosure) {
        self.authenticated = authenticated
    }
    
    // MARK: Body
    
    public var body: some View {
        ScrollView(
            .vertical,
            showsIndicators: false
        ) {
            Container(authenticated)
                .padding(.horizontal, 24)
                .padding(.top, containerTopPadding)
        }
        .background(Color.primary.colorInvert())
        .ignoresSafeArea()
        .overlay(ViewHeightGeometry())
        .onPreferenceChange(ViewHeightPreferenceKey.self) { height in
            containerTopPadding = height * 0.1
        }
        .interactiveDismissDisabled()
    }
    
}

// MARK: - Views

fileprivate extension LoginView {
    struct Container: View {

        // MARK: States
        
        @State private var isAuthenticating: Bool = false
        @State private var username: String = ""
        @State private var password: String = ""
        @State private var errorMessage: String?

        // MARK: Properties

        private var getUser: GetUserUseCase = .init()
        
        private let authenticated: AuthenticatedClosure
        
        init(_ authenticated: @escaping AuthenticatedClosure) {
            self.authenticated = authenticated
        }

        // MARK: Body
        
        var body: some View {
            VStack(spacing: 32) {
                Text(
                    "login.title.text",
                    bundle: .module
                )
                .font(.largeTitle)
                .fontWeight(.bold)
                .foregroundColor(.primary)
  
                LoginForm(
                    username: $username,
                    password: $password,
                    errorMessage: $errorMessage
                ) {
                    isAuthenticating = true
                }

                Button {
                    isAuthenticating = true
                } label: {
                    Label {
                        Text(
                            "login.button.log_in.text",
                            bundle: .module
                        )
                        .fontWeight(.semibold)
                    } icon: {
                        if isAuthenticating {
                            ProgressView()
                                .tint(.white)
                                .controlSize(.regular)
                        } else {
                            EmptyView()
                        }
                    }
                    .labelStyle(.logIn)
                }
                .tint(.red)
                .buttonStyle(.borderedProminent)
                .buttonBorderShape(.roundedRectangle(radius: 8))
                .controlSize(.large)
                .disabled(isLoginDisabled)
                .task(id: isAuthenticating) {
                    await authenticate()
                }
            }
        }
    }
}

// MARK: - Helpers

private extension LoginView.Container {
    
    // MARK: Computed
    
    var isLoginDisabled: Bool {
        username.isEmpty
            || password.isEmpty
            || errorMessage != nil
    }
    
    // MARK: Functions
    
    func authenticate() async {
        guard isAuthenticating else { return }
        
        defer { isAuthenticating = false }
        
        do {
            let user = try await getUser(
                username: username,
                password: password
            )
            
            // Added some throttle (1 second) not to hide the loading indicator right away.
            try await Task.sleep(nanoseconds: .Constants.secondInNanoseconds)

            authenticated(user)
        } catch APIClientError.authenticationFailed {
            errorMessage = "login.error.authentication_failed.text"
        } catch {
            errorMessage = "login.error.authentication_unknown.text"
        }
    }

}

// MARK: - Type aliases

public typealias AuthenticatedClosure = (User) -> Void

// MARK: - UInt64+Constants

private extension UInt64 {
    enum Constants {
        static let secondInNanoseconds = UInt64(1 * Double(NSEC_PER_SEC))
    }
}

// MARK: - Previews

struct LoginView_Previews: PreviewProvider {
    static var previews: some View {
        LoginView { _ in
            // authenticated closure.
        }
    }
}