gui-cs.Terminal.Gui/Terminal.Gui/Views/ListView.cs

using System.Collections;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using static Terminal.Gui.SpinnerStyle;

namespace Terminal.Gui;

/// <summary>Implement <see cref="IListDataSource"/> to provide custom rendering for a <see cref="ListView"/>.</summary>
public interface IListDataSource : IDisposable
{
    /// <summary>
    /// Event to raise when an item is added, removed, or moved, or the entire list is refreshed.
    /// </summary>
    event NotifyCollectionChangedEventHandler CollectionChanged;

    /// <summary>Returns the number of elements to display</summary>
    int Count { get; }

    /// <summary>Returns the maximum length of elements to display</summary>
    int Length { get; }

    /// <summary>
    /// Allow suspending the <see cref="CollectionChanged"/> event from being invoked,
    /// if <see langword="true"/>, otherwise is <see langword="false"/>.
    /// </summary>
    bool SuspendCollectionChangedEvent { get; set; }

    /// <summary>Should return whether the specified item is currently marked.</summary>
    /// <returns><see langword="true"/>, if marked, <see langword="false"/> otherwise.</returns>
    /// <param name="item">Item index.</param>
    bool IsMarked (int item);

    /// <summary>This method is invoked to render a specified item, the method should cover the entire provided width.</summary>
    /// <returns>The render.</returns>
    /// <param name="listView">The list view to render.</param>
    /// <param name="selected">Describes whether the item being rendered is currently selected by the user.</param>
    /// <param name="item">The index of the item to render, zero for the first item and so on.</param>
    /// <param name="col">The column where the rendering will start</param>
    /// <param name="line">The line where the rendering will be done.</param>
    /// <param name="width">The width that must be filled out.</param>
    /// <param name="start">The index of the string to be displayed.</param>
    /// <remarks>
    ///     The default color will be set before this method is invoked, and will be based on whether the item is selected
    ///     or not.
    /// </remarks>
    void Render (
        ListView listView,
        bool selected,
        int item,
        int col,
        int line,
        int width,
        int start = 0
    );

    /// <summary>Flags the item as marked.</summary>
    /// <param name="item">Item index.</param>
    /// <param name="value">If set to <see langword="true"/> value.</param>
    void SetMark (int item, bool value);

    /// <summary>Return the source as IList.</summary>
    /// <returns></returns>
    IList ToList ();
}

/// <summary>
///     ListView <see cref="View"/> renders a scrollable list of data where each item can be activated to perform an
///     action.
/// </summary>
/// <remarks>
///     <para>
///         The <see cref="ListView"/> displays lists of data and allows the user to scroll through the data. Items in
///         the can be activated firing an event (with the ENTER key or a mouse double-click). If the
///         <see cref="AllowsMarking"/> property is true, elements of the list can be marked by the user.
///     </para>
///     <para>
///         By default <see cref="ListView"/> uses <see cref="object.ToString"/> to render the items of any
///         <see cref="ObservableCollection{T}"/> object (e.g. arrays, <see cref="List{T}"/>, and other collections). Alternatively, an
///         object that implements <see cref="IListDataSource"/> can be provided giving full control of what is rendered.
///     </para>
///     <para>
///         <see cref="ListView"/> can display any object that implements the <see cref="IList"/> interface.
///         <see cref="string"/> values are converted into <see cref="string"/> values before rendering, and other values
///         are converted into <see cref="string"/> by calling <see cref="object.ToString"/> and then converting to
///         <see cref="string"/> .
///     </para>
///     <para>
///         To change the contents of the ListView, set the <see cref="Source"/> property (when providing custom
///         rendering via <see cref="IListDataSource"/>) or call <see cref="SetSource{T}"/> an <see cref="IList"/> is being
///         used.
///     </para>
///     <para>
///         When <see cref="AllowsMarking"/> is set to true the rendering will prefix the rendered items with [x] or [ ]
///         and bind the SPACE key to toggle the selection. To implement a different marking style set
///         <see cref="AllowsMarking"/> to false and implement custom rendering.
///     </para>
///     <para>
///         Searching the ListView with the keyboard is supported. Users type the first characters of an item, and the
///         first item that starts with what the user types will be selected.
///     </para>
/// </remarks>
public class ListView : View, IDesignable
{
    private bool _allowsMarking;
    private bool _allowsMultipleSelection = true;
    private int _lastSelectedItem = -1;
    private int _selected = -1;
    private IListDataSource _source;
    // TODO: ListView has been upgraded to use Viewport and ContentSize instead of the
    // TODO: bespoke _top and _left. It was a quick & dirty port. There is now duplicate logic
    // TODO: that could be removed. 
    //private int _top, _left;

    /// <summary>
    ///     Initializes a new instance of <see cref="ListView"/>. Set the <see cref="Source"/> property to display
    ///     something.
    /// </summary>
    public ListView ()
    {
        CanFocus = true;

        // Things this view knows how to do
        // 
        AddCommand (Command.Up, (ctx) =>
                                {
                                    if (RaiseSelecting (ctx) == true)
                                    {
                                        return true;
                                    }
                                    return MoveUp ();
                                });
        AddCommand (Command.Down, (ctx) =>
                                  {
                                      if (RaiseSelecting (ctx) == true)
                                      {
                                          return true;
                                      }
                                      return MoveDown ();
                                  });

        // TODO: add RaiseSelecting to all of these
        AddCommand (Command.ScrollUp, () => ScrollVertical (-1));
        AddCommand (Command.ScrollDown, () => ScrollVertical (1));
        AddCommand (Command.PageUp, () => MovePageUp ());
        AddCommand (Command.PageDown, () => MovePageDown ());
        AddCommand (Command.Start, () => MoveHome ());
        AddCommand (Command.End, () => MoveEnd ());
        AddCommand (Command.ScrollLeft, () => ScrollHorizontal (-1));
        AddCommand (Command.ScrollRight, () => ScrollHorizontal (1));

        // Accept (Enter key) - Raise Accept event - DO NOT advance state
        AddCommand (Command.Accept, (ctx) =>
                                    {
                                        if (RaiseAccepting (ctx) == true)
                                        {
                                            return true;
                                        }

                                        if (OnOpenSelectedItem ())
                                        {
                                            return true;
                                        }

                                        return false;
                                    });

        // Select (Space key and single-click) - If markable, change mark and raise Select event
        AddCommand (Command.Select, (ctx) =>
                                    {
                                        if (_allowsMarking)
                                        {
                                            if (RaiseSelecting (ctx) == true)
                                            {
                                                return true;
                                            }

                                            if (MarkUnmarkSelectedItem ())
                                            {
                                                return true;
                                            }
                                        }

                                        return false;
                                    });


        // Hotkey - If none set, select and raise Select event. SetFocus. - DO NOT raise Accept
        AddCommand (Command.HotKey, (ctx) =>
                                    {
                                        if (SelectedItem == -1)
                                        {
                                            SelectedItem = 0;
                                            if (RaiseSelecting (ctx) == true)
                                            {
                                                return true;

                                            }
                                        }

                                        return !SetFocus ();
                                    });

        AddCommand (Command.SelectAll, (ctx) => MarkAll((bool)ctx.KeyBinding?.Context!));

        // Default keybindings for all ListViews
        KeyBindings.Add (Key.CursorUp, Command.Up);
        KeyBindings.Add (Key.P.WithCtrl, Command.Up);

        KeyBindings.Add (Key.CursorDown, Command.Down);
        KeyBindings.Add (Key.N.WithCtrl, Command.Down);

        KeyBindings.Add (Key.PageUp, Command.PageUp);

        KeyBindings.Add (Key.PageDown, Command.PageDown);
        KeyBindings.Add (Key.V.WithCtrl, Command.PageDown);

        KeyBindings.Add (Key.Home, Command.Start);

        KeyBindings.Add (Key.End, Command.End);

        // Key.Space is already bound to Command.Select; this gives us select then move down
        KeyBindings.Add (Key.Space.WithShift, [Command.Select, Command.Down]);

        // Use the form of Add that lets us pass context to the handler
        KeyBindings.Add (Key.A.WithCtrl, new KeyBinding ([Command.SelectAll], KeyBindingScope.Focused, true));
        KeyBindings.Add (Key.U.WithCtrl, new KeyBinding ([Command.SelectAll], KeyBindingScope.Focused, false));

        SubviewsLaidOut += ListView_LayoutComplete;
    }

    private void ListView_LayoutComplete (object sender, LayoutEventArgs e)
    {
        SetContentSize (new Size (_source?.Length ?? Viewport.Width, _source?.Count ?? Viewport.Width));
    }

    /// <summary>Gets or sets whether this <see cref="ListView"/> allows items to be marked.</summary>
    /// <value>Set to <see langword="true"/> to allow marking elements of the list.</value>
    /// <remarks>
    ///     If set to <see langword="true"/>, <see cref="ListView"/> will render items marked items with "[x]", and
    ///     unmarked items with "[ ]". SPACE key will toggle marking. The default is <see langword="false"/>.
    /// </remarks>
    public bool AllowsMarking
    {
        get => _allowsMarking;
        set
        {
            _allowsMarking = value;
            SetNeedsDraw ();
        }
    }

    /// <summary>
    ///     If set to <see langword="true"/> more than one item can be selected. If <see langword="false"/> selecting an
    ///     item will cause all others to be un-selected. The default is <see langword="false"/>.
    /// </summary>
    public bool AllowsMultipleSelection
    {
        get => _allowsMultipleSelection;
        set
        {
            _allowsMultipleSelection = value;

            if (Source is { } && !_allowsMultipleSelection)
            {
                // Clear all selections except selected 
                for (var i = 0; i < Source.Count; i++)
                {
                    if (Source.IsMarked (i) && i != _selected)
                    {
                        Source.SetMark (i, false);
                    }
                }
            }

            SetNeedsDraw ();
        }
    }

    /// <summary>
    ///     Gets the <see cref="CollectionNavigator"/> that searches the <see cref="ListView.Source"/> collection as the
    ///     user types.
    /// </summary>
    public CollectionNavigator KeystrokeNavigator { get; } = new ();

    /// <summary>Gets or sets the leftmost column that is currently visible (when scrolling horizontally).</summary>
    /// <value>The left position.</value>
    public int LeftItem
    {
        get => Viewport.X;
        set
        {
            if (_source is null)
            {
                return;
            }

            if (value < 0 || (MaxLength > 0 && value >= MaxLength))
            {
                throw new ArgumentException ("value");
            }

            Viewport = Viewport with { X = value };
            SetNeedsDraw ();
        }
    }

    /// <summary>Gets the widest item in the list.</summary>
    public int MaxLength => _source?.Length ?? 0;

    /// <summary>Gets or sets the index of the currently selected item.</summary>
    /// <value>The selected item.</value>
    public int SelectedItem
    {
        get => _selected;
        set
        {
            if (_source is null || _source.Count == 0)
            {
                return;
            }

            if (value < -1 || value >= _source.Count)
            {
                throw new ArgumentException ("value");
            }

            _selected = value;
            OnSelectedChanged ();
        }
    }

    /// <summary>Gets or sets the <see cref="IListDataSource"/> backing this <see cref="ListView"/>, enabling custom rendering.</summary>
    /// <value>The source.</value>
    /// <remarks>Use <see cref="SetSource{T}"/> to set a new <see cref="IList"/> source.</remarks>
    public IListDataSource Source
    {
        get => _source;
        set
        {
            if (_source == value)
            {
                return;
            }

            _source?.Dispose ();
            _source = value;

            if (_source is { })
            {
                _source.CollectionChanged += Source_CollectionChanged;
            }

            SetContentSize (new Size (_source?.Length ?? Viewport.Width, _source?.Count ?? Viewport.Width));
            if (IsInitialized)
            {
               // Viewport = Viewport with { Y = 0 };
            }

            KeystrokeNavigator.Collection = _source?.ToList ();
            _selected = -1;
            _lastSelectedItem = -1;
            SetNeedsDraw ();
        }
    }


    private void Source_CollectionChanged (object sender, NotifyCollectionChangedEventArgs e)
    {
        SetContentSize (new Size (_source?.Length ?? Viewport.Width, _source?.Count ?? Viewport.Width));

        if (Source is { Count: > 0 } && _selected > Source.Count - 1)
        {
            SelectedItem = Source.Count - 1;
        }

        SetNeedsDraw ();

        OnCollectionChanged (e);
    }

    /// <summary>Gets or sets the index of the item that will appear at the top of the <see cref="View.Viewport"/>.</summary>
    /// <remarks>
    /// This a helper property for accessing <c>listView.Viewport.Y</c>.
    /// </remarks>
    /// <value>The top item.</value>
    public int TopItem
    {
        get => Viewport.Y;
        set
        {
            if (_source is null)
            {
                return;
            }

            Viewport = Viewport with { Y = value };
        }
    }

    /// <summary>
    ///     If <see cref="AllowsMarking"/> and <see cref="AllowsMultipleSelection"/> are both <see langword="true"/>,
    ///     marks all items.
    /// </summary>
    /// <param name="mark"><see langword="true"/> marks all items; otherwise unmarks all items.</param>
    /// <returns><see langword="true"/> if marking was successful.</returns>
    public bool MarkAll (bool mark)
    {
        if (!_allowsMarking)
        {
            return false;
        }

        if (AllowsMultipleSelection)
        {
            for (var i = 0; i < Source.Count; i++)
            {
                Source.SetMark (i, mark);
            }
            return true;
        }

        return false;
    }

    /// <summary>
    ///     If <see cref="AllowsMarking"/> and <see cref="AllowsMultipleSelection"/> are both <see langword="true"/>,
    ///     unmarks all marked items other than <see cref="SelectedItem"/>.
    /// </summary>
    /// <returns><see langword="true"/> if unmarking was successful.</returns>
    public bool UnmarkAllButSelected ()
    {
        if (!_allowsMarking)
        {
            return false;
        }

        if (!AllowsMultipleSelection)
        {
            for (var i = 0; i < Source.Count; i++)
            {
                if (Source.IsMarked (i) && i != _selected)
                {
                    Source.SetMark (i, false);

                    return true;
                }
            }
        }

        return true;
    }

    /// <summary>Ensures the selected item is always visible on the screen.</summary>
    public void EnsureSelectedItemVisible ()
    {
        if (SuperView?.IsInitialized == true)
        {
            if (_selected < Viewport.Y)
            {
                // TODO: The Max check here is not needed because, by default, Viewport enforces staying w/in ContentArea (View.ScrollSettings).
                Viewport = Viewport with { Y = _selected };
            }
            else if (Viewport.Height > 0 && _selected >= Viewport.Y + Viewport.Height)
            {
                Viewport = Viewport with { Y = _selected - Viewport.Height + 1 };
            }

            SubviewLayout -= ListView_LayoutStarted;
        }
        else
        {
            SubviewLayout += ListView_LayoutStarted;
        }
    }

    /// <summary>Marks the <see cref="SelectedItem"/> if it is not already marked.</summary>
    /// <returns><see langword="true"/> if the <see cref="SelectedItem"/> was marked.</returns>
    public bool MarkUnmarkSelectedItem ()
    {
        if (UnmarkAllButSelected ())
        {
            Source.SetMark (SelectedItem, !Source.IsMarked (SelectedItem));
            SetNeedsDraw ();

            return Source.IsMarked (SelectedItem);
        }

        // BUGBUG: Shouldn't this retrn Source.IsMarked (SelectedItem)

        return false;
    }

    /// <inheritdoc/>
    protected override bool OnMouseEvent (MouseEventArgs me)
    {
        if (!me.Flags.HasFlag (MouseFlags.Button1Clicked)
            && !me.Flags.HasFlag (MouseFlags.Button1DoubleClicked)
            && me.Flags != MouseFlags.WheeledDown
            && me.Flags != MouseFlags.WheeledUp
            && me.Flags != MouseFlags.WheeledRight
            && me.Flags != MouseFlags.WheeledLeft)
        {
            return false;
        }

        if (!HasFocus && CanFocus)
        {
            SetFocus ();
        }

        if (_source is null)
        {
            return false;
        }

        if (me.Flags == MouseFlags.WheeledDown)
        {
            ScrollVertical (1);

            return true;
        }

        if (me.Flags == MouseFlags.WheeledUp)
        {
            ScrollVertical (-1);

            return true;
        }

        if (me.Flags == MouseFlags.WheeledRight)
        {
            ScrollHorizontal (1);

            return true;
        }

        if (me.Flags == MouseFlags.WheeledLeft)
        {
            ScrollHorizontal (-1);

            return true;
        }

        if (me.Position.Y + Viewport.Y >= _source.Count
            || me.Position.Y + Viewport.Y < 0
            || me.Position.Y + Viewport.Y > Viewport.Y + Viewport.Height)
        {
            return true;
        }

        _selected = Viewport.Y + me.Position.Y;

        if (MarkUnmarkSelectedItem ())
        {
            // return true;
        }

        OnSelectedChanged ();
        SetNeedsDraw ();

        if (me.Flags == MouseFlags.Button1DoubleClicked)
        {
            return InvokeCommand (Command.Accept) is true;
        }

        return true;
    }

    /// <summary>Changes the <see cref="SelectedItem"/> to the next item in the list, scrolling the list if needed.</summary>
    /// <returns></returns>
    public virtual bool MoveDown ()
    {
        if (_source is null || _source.Count == 0)
        {
            // Do we set lastSelectedItem to -1 here?
            return false; //Nothing for us to move to
        }

        if (_selected >= _source.Count)
        {
            // If for some reason we are currently outside of the
            // valid values range, we should select the bottommost valid value.
            // This can occur if the backing data source changes.
            _selected = _source.Count - 1;
            OnSelectedChanged ();
            SetNeedsDraw ();
        }
        else if (_selected + 1 < _source.Count)
        {
            //can move by down by one.
            _selected++;

            if (_selected >= Viewport.Y + Viewport.Height)
            {
                Viewport = Viewport with { Y = Viewport.Y + 1 };
            }
            else if (_selected < Viewport.Y)
            {
                Viewport = Viewport with { Y = _selected };
            }

            OnSelectedChanged ();
            SetNeedsDraw ();
        }
        else if (_selected == 0)
        {
            OnSelectedChanged ();
            SetNeedsDraw ();
        }
        else if (_selected >= Viewport.Y + Viewport.Height)
        {
            Viewport = Viewport with { Y = _source.Count - Viewport.Height };
            SetNeedsDraw ();
        }

        return true;
    }

    /// <summary>Changes the <see cref="SelectedItem"/> to last item in the list, scrolling the list if needed.</summary>
    /// <returns></returns>
    public virtual bool MoveEnd ()
    {
        if (_source is { Count: > 0 } && _selected != _source.Count - 1)
        {
            _selected = _source.Count - 1;

            if (Viewport.Y + _selected > Viewport.Height - 1)
            {
                Viewport = Viewport with
                {
                    Y = _selected < Viewport.Height - 1
                            ? Math.Max (Viewport.Height - _selected + 1, 0)
                            : Math.Max (_selected - Viewport.Height + 1, 0)
                };
            }

            OnSelectedChanged ();
            SetNeedsDraw ();
        }

        return true;
    }

    /// <summary>Changes the <see cref="SelectedItem"/> to the first item in the list, scrolling the list if needed.</summary>
    /// <returns></returns>
    public virtual bool MoveHome ()
    {
        if (_selected != 0)
        {
            _selected = 0;
            Viewport = Viewport with { Y = _selected };
            OnSelectedChanged ();
            SetNeedsDraw ();
        }

        return true;
    }

    /// <summary>
    ///     Changes the <see cref="SelectedItem"/> to the item just below the bottom of the visible list, scrolling if
    ///     needed.
    /// </summary>
    /// <returns></returns>
    public virtual bool MovePageDown ()
    {
        if (_source is null)
        {
            return true;
        }

        int n = _selected + Viewport.Height;

        if (n >= _source.Count)
        {
            n = _source.Count - 1;
        }

        if (n != _selected)
        {
            _selected = n;

            if (_source.Count >= Viewport.Height)
            {
                Viewport = Viewport with { Y = _selected };
            }
            else
            {
                Viewport = Viewport with { Y = 0 };
            }

            OnSelectedChanged ();
            SetNeedsDraw ();
        }

        return true;
    }

    /// <summary>Changes the <see cref="SelectedItem"/> to the item at the top of the visible list.</summary>
    /// <returns></returns>
    public virtual bool MovePageUp ()
    {
        int n = _selected - Viewport.Height;

        if (n < 0)
        {
            n = 0;
        }

        if (n != _selected)
        {
            _selected = n;
            Viewport = Viewport with { Y = _selected };
            OnSelectedChanged ();
            SetNeedsDraw ();
        }

        return true;
    }

    /// <summary>Changes the <see cref="SelectedItem"/> to the previous item in the list, scrolling the list if needed.</summary>
    /// <returns></returns>
    public virtual bool MoveUp ()
    {
        if (_source is null || _source.Count == 0)
        {
            // Do we set lastSelectedItem to -1 here?
            return false; //Nothing for us to move to
        }

        if (_selected >= _source.Count)
        {
            // If for some reason we are currently outside of the
            // valid values range, we should select the bottommost valid value.
            // This can occur if the backing data source changes.
            _selected = _source.Count - 1;
            OnSelectedChanged ();
            SetNeedsDraw ();
        }
        else if (_selected > 0)
        {
            _selected--;

            if (_selected > Source.Count)
            {
                _selected = Source.Count - 1;
            }

            if (_selected < Viewport.Y)
            {
                Viewport = Viewport with { Y = _selected };
            }
            else if (_selected > Viewport.Y + Viewport.Height)
            {
                Viewport = Viewport with { Y = _selected - Viewport.Height + 1 };
            }

            OnSelectedChanged ();
            SetNeedsDraw ();
        }
        else if (_selected < Viewport.Y)
        {
            Viewport = Viewport with { Y = _selected };
            SetNeedsDraw ();
        }

        return true;
    }

    /// <inheritdoc/>
    protected override bool OnDrawingContent ()
    {
        Attribute current = ColorScheme?.Focus ?? Attribute.Default;
        SetAttribute (current);
        Move (0, 0);
        Rectangle f = Viewport;
        int item = Viewport.Y;
        bool focused = HasFocus;
        int col = _allowsMarking ? 2 : 0;
        int start = Viewport.X;

        for (var row = 0; row < f.Height; row++, item++)
        {
            bool isSelected = item == _selected;

            Attribute newcolor = focused ? isSelected ? ColorScheme.Focus : GetNormalColor () :
                                 isSelected ? ColorScheme.HotNormal : GetNormalColor ();

            if (newcolor != current)
            {
                SetAttribute (newcolor);
                current = newcolor;
            }

            Move (0, row);

            if (_source is null || item >= _source.Count)
            {
                for (var c = 0; c < f.Width; c++)
                {
                    Driver?.AddRune ((Rune)' ');
                }
            }
            else
            {
                var rowEventArgs = new ListViewRowEventArgs (item);
                OnRowRender (rowEventArgs);

                if (rowEventArgs.RowAttribute is { } && current != rowEventArgs.RowAttribute)
                {
                    current = (Attribute)rowEventArgs.RowAttribute;
                    SetAttribute (current);
                }

                if (_allowsMarking)
                {
                    Driver?.AddRune (
                                    _source.IsMarked (item) ? AllowsMultipleSelection ? Glyphs.CheckStateChecked : Glyphs.Selected :
                                    AllowsMultipleSelection ? Glyphs.CheckStateUnChecked : Glyphs.UnSelected
                                   );
                    Driver?.AddRune ((Rune)' ');
                }

                Source.Render (this, isSelected, item, col, row, f.Width - col, start);
            }
        }
        return true;
    }

    /// <inheritdoc/>
    protected override void OnHasFocusChanged (bool newHasFocus, [CanBeNull] View currentFocused, [CanBeNull] View newFocused)
    {
        if (newHasFocus && _lastSelectedItem != _selected)
        {
            EnsureSelectedItemVisible ();
        }
    }

    /// <summary>Invokes the <see cref="OpenSelectedItem"/> event if it is defined.</summary>
    /// <returns><see langword="true"/> if the <see cref="OpenSelectedItem"/> event was fired.</returns>
    public bool OnOpenSelectedItem ()
    {
        if (_source is null || _source.Count <= _selected || _selected < 0 || OpenSelectedItem is null)
        {
            return false;
        }

        object value = _source.ToList () [_selected];

        OpenSelectedItem?.Invoke (this, new ListViewItemEventArgs (_selected, value));

        // BUGBUG: this should not blindly return true.
        return true;
    }

    /// <inheritdoc/>
    protected override bool OnKeyDown (Key a)
    {
        // If marking is enabled and the user presses the space key don't let CollectionNavigator
        // at it
        if (AllowsMarking)
        {
            var keys = KeyBindings.GetKeysFromCommands (Command.Select);

            if (keys.Contains (a))
            {
                return false;
            }

            keys = KeyBindings.GetKeysFromCommands ([Command.Select, Command.Down]);

            if (keys.Contains (a))
            {
                return false;
            }

        }

        // Enable user to find & select an item by typing text
        if (CollectionNavigatorBase.IsCompatibleKey (a))
        {
            int? newItem = KeystrokeNavigator?.GetNextMatchingItem (SelectedItem, (char)a);

            if (newItem is int && newItem != -1)
            {
                SelectedItem = (int)newItem;
                EnsureSelectedItemVisible ();
                SetNeedsDraw ();

                return true;
            }
        }

        return false;
    }

    /// <summary>Virtual method that will invoke the <see cref="RowRender"/>.</summary>
    /// <param name="rowEventArgs"></param>
    public virtual void OnRowRender (ListViewRowEventArgs rowEventArgs) { RowRender?.Invoke (this, rowEventArgs); }

    // TODO: Use standard event model
    /// <summary>Invokes the <see cref="SelectedItemChanged"/> event if it is defined.</summary>
    /// <returns></returns>
    public virtual bool OnSelectedChanged ()
    {
        if (_selected != _lastSelectedItem)
        {
            object value = _source?.Count > 0 ? _source.ToList () [_selected] : null;
            SelectedItemChanged?.Invoke (this, new ListViewItemEventArgs (_selected, value));
            _lastSelectedItem = _selected;
            EnsureSelectedItemVisible ();

            return true;
        }

        return false;
    }

    /// <summary>This event is raised when the user Double Clicks on an item or presses ENTER to open the selected item.</summary>
    public event EventHandler<ListViewItemEventArgs> OpenSelectedItem;

    ///// <inheritdoc/>
    //public override Point? PositionCursor ()
    //{
    //    int x = 0;
    //    int y = _selected - Viewport.Y;
    //    if (!_allowsMarking)
    //    {
    //        x = Viewport.Width - 1;
    //    }

    //    Move (x, y);

    //    return null; // Don't show the cursor
    //}

    /// <summary>This event is invoked when this <see cref="ListView"/> is being drawn before rendering.</summary>
    public event EventHandler<ListViewRowEventArgs> RowRender;

    /// <summary>This event is raised when the selected item in the <see cref="ListView"/> has changed.</summary>
    public event EventHandler<ListViewItemEventArgs> SelectedItemChanged;

    /// <summary>
    /// Event to raise when an item is added, removed, or moved, or the entire list is refreshed.
    /// </summary>
    public event NotifyCollectionChangedEventHandler CollectionChanged;

    /// <summary>Sets the source of the <see cref="ListView"/> to an <see cref="IList"/>.</summary>
    /// <value>An object implementing the IList interface.</value>
    /// <remarks>
    ///     Use the <see cref="Source"/> property to set a new <see cref="IListDataSource"/> source and use custom
    ///     rendering.
    /// </remarks>
    public void SetSource<T> (ObservableCollection<T> source)
    {
        if (source is null && Source is not ListWrapper<T>)
        {
            Source = null;
        }
        else
        {
            Source = new ListWrapper<T> (source);
        }
    }

    /// <summary>Sets the source to an <see cref="IList"/> value asynchronously.</summary>
    /// <value>An item implementing the IList interface.</value>
    /// <remarks>
    ///     Use the <see cref="Source"/> property to set a new <see cref="IListDataSource"/> source and use custom
    ///     rendering.
    /// </remarks>
    public Task SetSourceAsync<T> (ObservableCollection<T> source)
    {
        return Task.Factory.StartNew (
                                      () =>
                                      {
                                          if (source is null && (Source is null || !(Source is ListWrapper<T>)))
                                          {
                                              Source = null;
                                          }
                                          else
                                          {
                                              Source = new ListWrapper<T> (source);
                                          }

                                          return source;
                                      },
                                      CancellationToken.None,
                                      TaskCreationOptions.DenyChildAttach,
                                      TaskScheduler.Default
                                     );
    }

    private void ListView_LayoutStarted (object sender, LayoutEventArgs e) { EnsureSelectedItemVisible (); }
    /// <summary>
    /// Call the event to raises the <see cref="CollectionChanged"/>.
    /// </summary>
    /// <param name="e"></param>
    protected virtual void OnCollectionChanged (NotifyCollectionChangedEventArgs e) { CollectionChanged?.Invoke (this, e); }

    /// <inheritdoc />
    protected override void Dispose (bool disposing)
    {
        _source?.Dispose ();

        base.Dispose (disposing);
    }

    /// <summary>
    /// Allow suspending the <see cref="CollectionChanged"/> event from being invoked,
    /// </summary>
    public void SuspendCollectionChangedEvent ()
    {
        if (Source is { })
        {
            Source.SuspendCollectionChangedEvent = true;
        }
    }

    /// <summary>
    /// Allow resume the <see cref="CollectionChanged"/> event from being invoked,
    /// </summary>
    public void ResumeSuspendCollectionChangedEvent ()
    {
        if (Source is { })
        {
            Source.SuspendCollectionChangedEvent = false;
        }
    }

    /// <inheritdoc />
    public bool EnableForDesign ()
    {
        var source = new ListWrapper<string> (["List Item 1", "List Item two", "List Item Quattro", "Last List Item"]);
        Source = source;

        return true;
    }
}

/// <summary>
///     Provides a default implementation of <see cref="IListDataSource"/> that renders <see cref="ListView"/> items
///     using <see cref="object.ToString()"/>.
/// </summary>
public class ListWrapper<T> : IListDataSource, IDisposable
{
    private int _count;
    private BitArray _marks;
    private readonly ObservableCollection<T> _source;

    /// <inheritdoc/>
    public ListWrapper (ObservableCollection<T> source)
    {
        if (source is { })
        {
            _count = source.Count;
            _marks = new BitArray (_count);
            _source = source;
            _source.CollectionChanged += Source_CollectionChanged;
            Length = GetMaxLengthItem ();
        }
    }

    private void Source_CollectionChanged (object sender, NotifyCollectionChangedEventArgs e)
    {
        if (!SuspendCollectionChangedEvent)
        {
            CheckAndResizeMarksIfRequired ();
            CollectionChanged?.Invoke (sender, e);
        }
    }

    /// <inheritdoc />
    public event NotifyCollectionChangedEventHandler CollectionChanged;

    /// <inheritdoc/>
    public int Count => _source?.Count ?? 0;

    /// <inheritdoc/>
    public int Length { get; private set; }

    private bool _suspendCollectionChangedEvent;

    /// <inheritdoc />
    public bool SuspendCollectionChangedEvent
    {
        get => _suspendCollectionChangedEvent;
        set
        {
            _suspendCollectionChangedEvent = value;

            if (!_suspendCollectionChangedEvent)
            {
                CheckAndResizeMarksIfRequired ();
            }
        }
    }

    private void CheckAndResizeMarksIfRequired ()
    {
        if (_source != null && _count != _source.Count)
        {
            _count = _source.Count;
            BitArray newMarks = new BitArray (_count);
            for (var i = 0; i < Math.Min (_marks.Length, newMarks.Length); i++)
            {
                newMarks [i] = _marks [i];
            }
            _marks = newMarks;

            Length = GetMaxLengthItem ();
        }
    }

    /// <inheritdoc/>
    public void Render (
        ListView container,
        bool marked,
        int item,
        int col,
        int line,
        int width,
        int start = 0
    )
    {
        container.Move (Math.Max (col - start, 0), line);

        if (_source is { })
        {
            object t = _source [item];

            if (t is null)
            {
                RenderUstr (container, "", col, line, width);
            }
            else
            {
                if (t is string s)
                {
                    RenderUstr (container, s, col, line, width, start);
                }
                else
                {
                    RenderUstr (container, t.ToString (), col, line, width, start);
                }
            }
        }
    }

    /// <inheritdoc/>
    public bool IsMarked (int item)
    {
        if (item >= 0 && item < _count)
        {
            return _marks [item];
        }

        return false;
    }

    /// <inheritdoc/>
    public void SetMark (int item, bool value)
    {
        if (item >= 0 && item < _count)
        {
            _marks [item] = value;
        }
    }

    /// <inheritdoc/>
    public IList ToList () { return _source; }

    /// <inheritdoc/>
    public int StartsWith (string search)
    {
        if (_source is null || _source?.Count == 0)
        {
            return -1;
        }

        for (var i = 0; i < _source.Count; i++)
        {
            object t = _source [i];

            if (t is string u)
            {
                if (u.ToUpper ().StartsWith (search.ToUpperInvariant ()))
                {
                    return i;
                }
            }
            else if (t is string s)
            {
                if (s.StartsWith (search, StringComparison.InvariantCultureIgnoreCase))
                {
                    return i;
                }
            }
        }

        return -1;
    }

    private int GetMaxLengthItem ()
    {
        if (_source is null || _source?.Count == 0)
        {
            return 0;
        }

        var maxLength = 0;

        for (var i = 0; i < _source.Count; i++)
        {
            object t = _source [i];
            int l;

            if (t is string u)
            {
                l = u.GetColumns ();
            }
            else if (t is string s)
            {
                l = s.Length;
            }
            else
            {
                l = t.ToString ().Length;
            }

            if (l > maxLength)
            {
                maxLength = l;
            }
        }

        return maxLength;
    }

    private void RenderUstr (View driver, string ustr, int col, int line, int width, int start = 0)
    {
        string str = start > ustr.GetColumns () ? string.Empty : ustr.Substring (Math.Min (start, ustr.ToRunes ().Length - 1));
        string u = TextFormatter.ClipAndJustify (str, width, Alignment.Start);
        driver.AddStr (u);
        width -= u.GetColumns ();

        while (width-- > 0)
        {
            driver.AddRune ((Rune)' ');
        }
    }

    /// <inheritdoc />
    public void Dispose ()
    {
        if (_source is { })
        {
            _source.CollectionChanged -= Source_CollectionChanged;
        }
    }
}