<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MyApp.Views.LoginPage">
    <ContentPage.Content>
        <StackLayout VerticalOptions="Center" Padding="10">
            <Label Text="Username" />
            <Entry x:Name="UsernameEntry" Text="{Binding Username}" />
            <Label Text="Password" />
            <Entry x:Name="PasswordEntry" Text="{Binding Password}" IsPassword="true" />
            <Button Text="Log in" Command="{Binding LoginCommand}" />
            <Button Text="Cancel" Command="{Binding CancelCommand}" />
        </StackLayout>
    </ContentPage.Content>
</ContentPage>

namespace MyApp.Views
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class LoginPage : ContentPage
    {
        public LoginPage(LoginViewModel vm)
        {
            vm.ShowEmptyUsernameAlert += () => DisplayAlert(string.Empty, "Username is empty.", "OK");
            vm.ShowEmptyPasswordAlert += () => DisplayAlert(string.Empty, "Password is empty.", "OK");
            vm.ShowInvalidLoginAlert += () => DisplayAlert(string.Empty, "Wrong user or password.", "OK");
            vm.ShowNoConnectionAlert += () => DisplayAlert(string.Empty, "Can't connect to the service. Are you connected to the Internet?", "OK");
            vm.ShowOtherErrorAlert += (message) => DisplayAlert("We're sorry", message, "OK");
            BindingContext = vm;
            InitializeComponent();
        }
    }
}

namespace MyApp.ViewModels
{
    public class LoginViewModel : INotifyPropertyChanged
    {
        INavigation _navigation;

        public LoginViewModel(INavigation navigation)
        {
            _navigation = navigation;
        }

        public event PropertyChangedEventHandler PropertyChanged;
        public Action ShowEmptyUsernameAlert;
        public Action ShowEmptyPasswordAlert;
        public Action ShowInvalidLoginAlert;
        public Action ShowNoConnectionAlert;
        public Action<string> ShowOtherErrorAlert;

        string _username;
        string _password;

        public string Username
        {
            get => _username;
            set
            {
                _username = value;
                PropertyChanged(this, new PropertyChangedEventArgs("Username"));
            }
        }

        public string Password
        {
            get => _password;
            set
            {
                _password = value;
                PropertyChanged(this, new PropertyChangedEventArgs("Password"));
            }
        }

        public ICommand LoginCommand => new Command(async () =>
        {
            // Validate fields.

            if (string.IsNullOrEmpty(Username))
            {
                ShowEmptyUsernameAlert();
                return;
            }

            if (string.IsNullOrEmpty(Password))
            {
                ShowEmptyPasswordAlert();
                return;
            }

            // Display a loading animation. (Rg.Plugins.Popup)

            var loadingPage = new LoadingPopupPage();
            await _navigation.PushPopupAsync(loadingPage);

            // Verify the login.

            try
            {
                var customer = await App.Api.LoginCustomerAsync(Username, Password);
                Properties.CrmId.Set(customer.CrmId);
                LoginSucceeded?.Invoke(this, new LoginSuccessEventArgs(customer));
                await _navigation.PopModalAsync(); // Close the login modal.
            }
            catch (VerifyLoginFaultException)
            {
                ShowInvalidLoginAlert();
            }
            catch (SoapFaultException ex)
            {
                Crashes.TrackError(ex);
                ShowOtherErrorAlert(ex.Message);
            }
            catch (WebException ex)
            {
                Crashes.TrackError(ex);
                switch (ex.Status)
                {
                    case WebExceptionStatus.Timeout:
                    case WebExceptionStatus.ConnectFailure:
                    case WebExceptionStatus.NameResolutionFailure:
                        ShowNoConnectionAlert();
                        break;
                    default:
                        ShowOtherErrorAlert(ex.Message);
                        break;
                }
            }
            catch (Exception ex)
            {
                Crashes.TrackError(ex);
                ShowOtherErrorAlert(ex.Message);
            }
            finally
            {
                await _navigation.RemovePopupPageAsync(loadingPage);
            }
        });

        public ICommand CancelCommand => new Command(async () => await _navigation.PopModalAsync());

        public class LoginSuccessEventArgs : EventArgs
        {
            public Customer Customer { get; set; }
            public LoginSuccessEventArgs(Customer customer) => Customer = customer;
        }

        public event EventHandler<LoginSuccessEventArgs> LoginSucceeded;
    }
}