gui-cs.Terminal.Gui/Terminal.Gui/View/View.ColorScheme.cs

#nullable enable
using System.ComponentModel;

namespace Terminal.Gui;

public partial class View
{
    // TODO: See https://github.com/gui-cs/Terminal.Gui/issues/4014
    // TODO: See https://github.com/gui-cs/Terminal.Gui/issues/4016
    // TODO: Enable ability to tell if ColorScheme was explicitly set; ColorScheme, as is, hides this.
    internal ColorScheme? _colorScheme;

    /// <summary>The color scheme for this view, if it is not defined, it returns the <see cref="SuperView"/>'s color scheme.</summary>
    public virtual ColorScheme? ColorScheme
    {
        // BUGBUG: This prevents the ability to know if ColorScheme was explicitly set or not.
        get => _colorScheme ?? SuperView?.ColorScheme;
        set
        {
            if (_colorScheme == value)
            {
                return;
            }

            _colorScheme = value;

            // BUGBUG: This should be in Border.cs somehow
            if (Border is { } && Border.LineStyle != LineStyle.None && Border.ColorScheme is { })
            {
                Border.ColorScheme = _colorScheme;
            }

            SetNeedsDraw ();
        }
    }

    /// <summary>Determines the current <see cref="ColorScheme"/> based on the <see cref="Enabled"/> value.</summary>
    /// <returns>
    ///     <see cref="ColorScheme.Focus"/> if <see cref="Enabled"/> is <see langword="true"/> or
    ///     <see cref="ColorScheme.Disabled"/> if <see cref="Enabled"/> is <see langword="false"/>. If it's
    ///     overridden can return other values.
    /// </returns>
    public virtual Attribute GetFocusColor ()
    {
        Attribute currAttribute = ColorScheme?.Normal ?? Attribute.Default;
        var newAttribute = new Attribute ();
        CancelEventArgs<Attribute> args = new (in currAttribute, ref newAttribute);
        GettingFocusColor?.Invoke (this, args);

        if (args.Cancel)
        {
            return args.NewValue;
        }

        ColorScheme? cs = ColorScheme ?? new ();

        return Enabled ? GetColor (cs.Focus) : cs.Disabled;
    }

    /// <summary>
    ///     Raised the Focus Color is being retrieved, from <see cref="GetFocusColor"/>. Cancel the event and set the new
    ///     attribute in the event args to
    ///     a different value to change the focus color.
    /// </summary>
    public event EventHandler<CancelEventArgs<Attribute>>? GettingFocusColor;

    /// <summary>Determines the current <see cref="ColorScheme"/> based on the <see cref="Enabled"/> value.</summary>
    /// <returns>
    ///     <see cref="ColorScheme.Focus"/> if <see cref="Enabled"/> is <see langword="true"/> or
    ///     <see cref="ColorScheme.Disabled"/> if <see cref="Enabled"/> is <see langword="false"/>. If it's
    ///     overridden can return other values.
    /// </returns>
    public virtual Attribute GetHotFocusColor ()
    {
        Attribute currAttribute = ColorScheme?.Normal ?? Attribute.Default;
        var newAttribute = new Attribute ();
        CancelEventArgs<Attribute> args = new (in currAttribute, ref newAttribute);
        GettingHotFocusColor?.Invoke (this, args);

        if (args.Cancel)
        {
            return args.NewValue;
        }

        ColorScheme? cs = ColorScheme ?? new ();

        return Enabled ? GetColor (cs.HotFocus) : cs.Disabled;
    }

    /// <summary>
    ///     Raised the HotFocus Color is being retrieved, from <see cref="GetHotFocusColor"/>. Cancel the event and set the new
    ///     attribute in the event args to
    ///     a different value to change the focus color.
    /// </summary>
    public event EventHandler<CancelEventArgs<Attribute>>? GettingHotFocusColor;

    /// <summary>Determines the current <see cref="ColorScheme"/> based on the <see cref="Enabled"/> value.</summary>
    /// <returns>
    ///     <see cref="ColorScheme.HotNormal"/> if <see cref="Enabled"/> is <see langword="true"/> or
    ///     <see cref="ColorScheme.Disabled"/> if <see cref="Enabled"/> is <see langword="false"/>. If it's
    ///     overridden can return other values.
    /// </returns>
    public virtual Attribute GetHotNormalColor ()
    {
        Attribute currAttribute = ColorScheme?.Normal ?? Attribute.Default;
        var newAttribute = new Attribute ();
        CancelEventArgs<Attribute> args = new (in currAttribute, ref newAttribute);
        GettingHotNormalColor?.Invoke (this, args);

        if (args.Cancel)
        {
            return args.NewValue;
        }

        ColorScheme? cs = ColorScheme ?? new ();

        return Enabled ? GetColor (cs.HotNormal) : cs.Disabled;
    }

    /// <summary>
    ///     Raised the HotNormal Color is being retrieved, from <see cref="GetHotNormalColor"/>. Cancel the event and set the
    ///     new attribute in the event args to
    ///     a different value to change the focus color.
    /// </summary>
    public event EventHandler<CancelEventArgs<Attribute>>? GettingHotNormalColor;

    /// <summary>Determines the current <see cref="ColorScheme"/> based on the <see cref="Enabled"/> value.</summary>
    /// <returns>
    ///     <see cref="ColorScheme.Normal"/> if <see cref="Enabled"/> is <see langword="true"/> or
    ///     <see cref="ColorScheme.Disabled"/> if <see cref="Enabled"/> is <see langword="false"/>. If it's
    ///     overridden can return other values.
    /// </returns>
    public virtual Attribute GetNormalColor ()
    {
        Attribute currAttribute = ColorScheme?.Normal ?? Attribute.Default;
        var newAttribute = new Attribute ();
        CancelEventArgs<Attribute> args = new (in currAttribute, ref newAttribute);
        GettingNormalColor?.Invoke (this, args);

        if (args.Cancel)
        {
            return args.NewValue;
        }

        ColorScheme? cs = ColorScheme ?? new ();
        Attribute disabled = new (cs.Disabled.Foreground, cs.Disabled.Background);

        if (Diagnostics.HasFlag (ViewDiagnosticFlags.Hover) && _hovering)
        {
            disabled = new (disabled.Foreground.GetDarkerColor (), disabled.Background.GetDarkerColor ());
        }

        return Enabled ? GetColor (cs.Normal) : disabled;
    }

    /// <summary>
    ///     Raised the Normal Color is being retrieved, from <see cref="GetNormalColor"/>. Cancel the event and set the new
    ///     attribute in the event args to
    ///     a different value to change the focus color.
    /// </summary>
    public event EventHandler<CancelEventArgs<Attribute>>? GettingNormalColor;

    /// <summary>
    ///     Sets the Normal attribute if the setting process is not canceled. It triggers an event and checks for
    ///     cancellation before proceeding.
    /// </summary>
    public void SetNormalAttribute ()
    {
        if (OnSettingNormalAttribute ())
        {
            return;
        }

        var args = new CancelEventArgs ();
        SettingNormalAttribute?.Invoke (this, args);

        if (args.Cancel)
        {
            return;
        }

        if (ColorScheme is { })
        {
            SetAttribute (GetNormalColor ());
        }
    }

    /// <summary>
    ///     Called when the normal attribute for the View is to be set. This is called before the View is drawn.
    /// </summary>
    /// <returns><see langword="true"/> to stop default behavior.</returns>
    protected virtual bool OnSettingNormalAttribute () { return false; }

    /// <summary>Raised  when the normal attribute for the View is to be set. This is raised before the View is drawn.</summary>
    /// <returns>
    ///     Set <see cref="CancelEventArgs.Cancel"/> to <see langword="true"/> to stop default behavior.
    /// </returns>
    public event EventHandler<CancelEventArgs>? SettingNormalAttribute;

    private Attribute GetColor (Attribute inputAttribute)
    {
        Attribute attr = inputAttribute;

        if (Diagnostics.HasFlag (ViewDiagnosticFlags.Hover) && _hovering)
        {
            attr = new (attr.Foreground.GetDarkerColor (), attr.Background.GetDarkerColor ());
        }

        return attr;
    }
}