DodoSSH/src/DodoSSH.Client.App/Views/ConnectPrompt.axaml.cs

using Avalonia;
using Avalonia.Controls;
using Avalonia.Input;
using Avalonia.Interactivity;
using Avalonia.Threading;
using DodoSSH.Client.Shell.ViewModels;

namespace DodoSSH.Client.App.Views;

/// <summary>The empty terminal's prompt: what to connect to, and its password when one is needed.</summary>
/// <remarks>
/// The keys and the caret live here, as the palette's do in <see cref="QuickConnect"/> and for its reason: a
/// <see cref="UserControl"/> hosts in a bare window under the headless harness, and the window itself cannot
/// be shown there at all.
/// </remarks>
internal sealed partial class ConnectPrompt : UserControl
{
    public ConnectPrompt()
    {
        InitializeComponent();

        // Tunnelled, for the reason QuickConnect gives: the prompt owns Enter, Escape and Tab while the caret is
        // in it, and a text box on the route must not get to them first.
        AddHandler(KeyDownEvent, OnPromptKey, RoutingStrategies.Tunnel);

        // The password line appearing, or going, moves the caret with it: Enter on a name that needs a password
        // should leave somebody typing the password, and Escape off it should leave them editing the name.
        PasswordLine.PropertyChanged += OnLineChanged;
    }

    /// <summary>The first line's box, for the caret and for the tests.</summary>
    internal TextBox TargetBox => Target;

    /// <summary>The password line's box, for the caret and for the tests.</summary>
    internal TextBox PasswordBox => Password;

    private MainWindowViewModel? Shell => DataContext as MainWindowViewModel;

    /// <inheritdoc />
    protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
    {
        base.OnPropertyChanged(change);

        // Posted, for the reason QuickConnect.TakeKeyboard gives at length: at the instant this becomes
        // visible its boxes are not in the visual tree yet, and focus is refused to anything that is not.
        if (change.Property == IsVisibleProperty && change.GetNewValue<bool>())
        {
            Dispatcher.UIThread.Post(TakeKeyboard, DispatcherPriority.Loaded);
        }
    }

    private void OnLineChanged(object? sender, AvaloniaPropertyChangedEventArgs e)
    {
        if (e.Property == IsVisibleProperty && IsVisible)
        {
            Dispatcher.UIThread.Post(TakeKeyboard, DispatcherPriority.Loaded);
        }
    }

    /// <summary>Puts the caret on whichever line is asking.</summary>
    /// <remarks>
    /// Both halves, for the reason <see cref="NativeKeyboardFocus"/> gives: the terminal's WebView can still
    /// hold the native window's focus after it has been collapsed, and an Avalonia focus without the native
    /// call is a caret that receives nothing.
    /// </remarks>
    private void TakeKeyboard()
    {
        if (!IsEffectivelyVisible)
        {
            return;
        }

        if (TopLevel.GetTopLevel(this) is Window window)
        {
            NativeKeyboardFocus.ReturnTo(window);
        }

        if (PasswordLine.IsVisible)
        {
            Password.Focus();
        }
        else
        {
            Target.Focus();
            Target.CaretIndex = Target.Text?.Length ?? 0;
        }
    }

    private void OnPromptKey(object? sender, KeyEventArgs e)
    {
        if (Shell is not { IsConnectPromptShowing: true } shell || e.KeyModifiers != KeyModifiers.None)
        {
            return;
        }

        switch (e.Key)
        {
            case Key.Enter:
                // Fire-and-forget, as the palette's is: the command reports its own refusals on the prompt,
                // and a connection's progress and failure in the tab it opens.
                _ = shell.SubmitPromptCommand.ExecuteAsync(null);
                e.Handled = true;
                break;

            case Key.Escape:
                shell.CancelPromptCommand.Execute(null);
                e.Handled = true;
                break;

            case Key.Tab:
                // Only when there is something to complete to; otherwise Tab moves the focus, as it always does.
                e.Handled = shell.CompletePrompt();

                if (e.Handled)
                {
                    Target.CaretIndex = Target.Text?.Length ?? 0;
                }

                break;

            default:
                break;
        }
    }
}