gui-cs.Terminal.Gui/Terminal.Gui/Views/Scroll/ScrollBar.cs

#nullable enable

using System.ComponentModel;

namespace Terminal.Gui;

/// <summary>
///     Provides a visual indicator that content can be scrolled. ScrollBars consist of two buttons, one each for scrolling
///     forward or backwards, a <see cref="Scroll"/> that can be dragged
///     to scroll continuously. ScrollBars can be oriented either horizontally or vertically and support the user dragging
///     and clicking with the mouse to scroll.
/// </summary>
/// <remarks>
///     <para>
///         <see cref="SliderPosition"/> indicates the number of rows or columns the Scroll has moved from 0.
///     </para>
/// </remarks>
public class ScrollBar : View, IOrientation, IDesignable
{
    private readonly Scroll _scroll;
    private readonly Button _decreaseButton;
    private readonly Button _increaseButton;

    /// <inheritdoc/>
    public ScrollBar ()
    {
        CanFocus = false;

        _scroll = new ();
        _scroll.SliderPositionChanging += OnScrollOnSliderPositionChanging;
        _scroll.SliderPositionChanged += OnScrollOnSliderPositionChanged;
        _scroll.ContentPositionChanging += OnScrollOnContentPositionChanging;
        _scroll.ContentPositionChanged += OnScrollOnContentPositionChanged;
        _scroll.SizeChanged += OnScrollOnSizeChanged;

        _decreaseButton = new ()
        {
            CanFocus = false,
            NoDecorations = true,
            NoPadding = true,
            ShadowStyle = ShadowStyle.None,
            WantContinuousButtonPressed = true
        };
        _decreaseButton.Accepting += OnDecreaseButtonOnAccept;

        _increaseButton = new ()
        {
            CanFocus = false,
            NoDecorations = true,
            NoPadding = true,
            ShadowStyle = ShadowStyle.None,
            WantContinuousButtonPressed = true
        };
        _increaseButton.Accepting += OnIncreaseButtonOnAccept;
        Add (_decreaseButton, _scroll, _increaseButton);

        _orientationHelper = new (this); // Do not use object initializer!
        _orientationHelper.Orientation = Orientation.Vertical;
        _orientationHelper.OrientationChanging += (sender, e) => OrientationChanging?.Invoke (this, e);
        _orientationHelper.OrientationChanged += (sender, e) => OrientationChanged?.Invoke (this, e);

        // This sets the width/height etc...
        OnOrientationChanged (Orientation);

        return;

        void OnDecreaseButtonOnAccept (object? s, CommandEventArgs e)
        {
            ContentPosition -= Increment;
            e.Cancel = true;
        }

        void OnIncreaseButtonOnAccept (object? s, CommandEventArgs e)
        {
            ContentPosition += Increment;
            e.Cancel = true;
        }
    }

    #region IOrientation members

    private readonly OrientationHelper _orientationHelper;

    /// <inheritdoc/>
    public Orientation Orientation
    {
        get => _orientationHelper.Orientation;
        set => _orientationHelper.Orientation = value;
    }

    /// <inheritdoc/>
    public event EventHandler<CancelEventArgs<Orientation>>? OrientationChanging;

    /// <inheritdoc/>
    public event EventHandler<EventArgs<Orientation>>? OrientationChanged;

    /// <inheritdoc/>
    public void OnOrientationChanged (Orientation newOrientation)
    {
        TextDirection = Orientation == Orientation.Vertical ? TextDirection.TopBottom_LeftRight : TextDirection.LeftRight_TopBottom;
        TextAlignment = Alignment.Center;
        VerticalTextAlignment = Alignment.Center;

        if (Orientation == Orientation.Vertical)
        {
            Width = 1;
            Height = Dim.Fill ();
        }
        else
        {
            Width = Dim.Fill ();
            Height = 1;
        }

        _scroll.Orientation = newOrientation;
    }

    #endregion

    private bool _autoHide = true;

    /// <summary>
    ///     Gets or sets whether <see cref="View.Visible"/> will be set to <see langword="false"/> if the dimension of the
    ///     scroll bar is greater than or equal to <see cref="Size"/>.
    /// </summary>
    public bool AutoHide
    {
        get => _autoHide;
        set
        {
            if (_autoHide != value)
            {
                _autoHide = value;

                if (!AutoHide)
                {
                    Visible = true;
                }

                SetNeedsLayout ();
            }
        }
    }

    /// <inheritdoc/>
    protected override void OnFrameChanged (in Rectangle frame) { ShowHide (); }

    private void ShowHide ()
    {
        if (!AutoHide || !IsInitialized)
        {
            return;
        }

        if (Orientation == Orientation.Vertical)
        {
            Visible = Frame.Height - (_decreaseButton.Frame.Height + _increaseButton.Frame.Height) < Size;
        }
        else
        {
            Visible = Frame.Width - (_decreaseButton.Frame.Width + _increaseButton.Frame.Width) < Size;
        }
    }

    /// <summary>
    ///     Gets or sets whether the Scroll will show the percentage the slider
    ///     takes up within the <see cref="Size"/>.
    /// </summary>
    public bool ShowPercent
    {
        get => _scroll.ShowPercent;
        set => _scroll.ShowPercent = value;
    }


    /// <summary>Get or sets if the view-port is kept in all visible area of this <see cref="ScrollBar"/>.</summary>
    public bool KeepContentInAllViewport
    {
        //get => _scroll.KeepContentInAllViewport;
        //set => _scroll.KeepContentInAllViewport = value;
        get;
        set;
    }

    /// <summary>Gets or sets the position of the slider within the ScrollBar's Viewport.</summary>
    /// <value>The position.</value>
    public int SliderPosition
    {
        get => _scroll.SliderPosition;
        set => _scroll.SliderPosition = value;
    }

    private void OnScrollOnSliderPositionChanging (object? sender, CancelEventArgs<int> e) { SliderPositionChanging?.Invoke (this, e); }
    private void OnScrollOnSliderPositionChanged (object? sender, EventArgs<int> e) { SliderPositionChanged?.Invoke (this, e); }

    /// <summary>
    ///     Raised when the <see cref="SliderPosition"/> is changing. Set <see cref="CancelEventArgs.Cancel"/> to
    ///     <see langword="true"/> to prevent the position from being changed.
    /// </summary>
    public event EventHandler<CancelEventArgs<int>>? SliderPositionChanging;

    /// <summary>Raised when the <see cref="SliderPosition"/> has changed.</summary>
    public event EventHandler<EventArgs<int>>? SliderPositionChanged;


    /// <summary>
    ///     Gets or sets the size of the Scroll. This is the total size of the content that can be scrolled through.
    /// </summary>
    public int Size
    {
        get => _scroll.Size;
        set => _scroll.Size = value;
    }

    /// <summary>
    ///     Gets or sets the position of the ScrollSlider within the range of 0...<see cref="Size"/>.
    /// </summary>
    public int ContentPosition
    {
        get => _scroll.ContentPosition;
        set => _scroll.ContentPosition = value;
    }

    private void OnScrollOnContentPositionChanging (object? sender, CancelEventArgs<int> e) { ContentPositionChanging?.Invoke (this, e); }
    private void OnScrollOnContentPositionChanged (object? sender, EventArgs<int> e) { ContentPositionChanged?.Invoke (this, e); }

    /// <summary>
    ///     Raised when the <see cref="SliderPosition"/> is changing. Set <see cref="CancelEventArgs.Cancel"/> to
    ///     <see langword="true"/> to prevent the position from being changed.
    /// </summary>
    public event EventHandler<CancelEventArgs<int>>? ContentPositionChanging;

    /// <summary>Raised when the <see cref="SliderPosition"/> has changed.</summary>
    public event EventHandler<EventArgs<int>>? ContentPositionChanged;

    /// <summary>Raised when <see cref="Size"/> has changed.</summary>
    public event EventHandler<EventArgs<int>>? SizeChanged;

    private void OnScrollOnSizeChanged (object? sender, EventArgs<int> e)
    {
        ShowHide ();
        SizeChanged?.Invoke (this, e);
    }

    /// <summary>
    ///     Gets or sets the amount each click of the increment/decrement buttons and each
    ///     mouse wheel event will incremenet/decrement the <see cref="ContentPosition"/>.
    /// </summary>
    /// <remarks>
    ///     The default is 1.
    /// </remarks>
    public int Increment { get => _scroll.Increment; set => _scroll.Increment = value; }

    /// <inheritdoc/>
    protected override void OnSubviewLayout (LayoutEventArgs args) { PositionSubviews (); }

    private void PositionSubviews ()
    {
        if (Orientation == Orientation.Vertical)
        {
            _decreaseButton.Y = 0;
            _decreaseButton.X = 0;
            _decreaseButton.Width = Dim.Fill ();
            _decreaseButton.Height = 1;
            _decreaseButton.Title = Glyphs.UpArrow.ToString ();
            _increaseButton.Y = Pos.Bottom (_scroll);
            _increaseButton.X = 0;
            _increaseButton.Width = Dim.Fill ();
            _increaseButton.Height = 1;
            _increaseButton.Title = Glyphs.DownArrow.ToString ();
            _scroll.X = 0;
            _scroll.Y = Pos.Bottom (_decreaseButton);
            _scroll.Height = Dim.Fill (1);
            _scroll.Width = Dim.Fill ();
        }
        else
        {
            _decreaseButton.Y = 0;
            _decreaseButton.X = 0;
            _decreaseButton.Width = 1;
            _decreaseButton.Height = Dim.Fill ();
            _decreaseButton.Title = Glyphs.LeftArrow.ToString ();
            _increaseButton.Y = 0;
            _increaseButton.X = Pos.Right (_scroll);
            _increaseButton.Width = 1;
            _increaseButton.Height = Dim.Fill ();
            _increaseButton.Title = Glyphs.RightArrow.ToString ();
            _scroll.Y = 0;
            _scroll.X = Pos.Right (_decreaseButton);
            _scroll.Width = Dim.Fill (1);
            _scroll.Height = Dim.Fill ();
        }
    }

    /// <inheritdoc/>
    public bool EnableForDesign ()
    {
        OrientationChanged += (sender, args) =>
                              {
                                  if (args.CurrentValue == Orientation.Vertical)
                                  {
                                      Width = 1;
                                      Height = Dim.Fill ();
                                  }
                                  else
                                  {
                                      Width = Dim.Fill ();
                                      Height = 1;
                                  }
                              };

        Width = 1;
        Height = Dim.Fill ();
        Size = 200;
        SliderPosition = 10;
        //ShowPercent = true;
        return true;
    }
}