gui-cs.Terminal.Gui/Terminal.Gui/Drawing/Color/StandardColors.cs

using System.Collections.Frozen;
using System.Collections.Immutable;
using System.Diagnostics.CodeAnalysis;

namespace Terminal.Gui.Drawing;

/// <summary>
///     Helper class for transforming to and from <see cref="StandardColor"/> enum.
/// </summary>
internal static class StandardColors
{
    // Lazy initialization to avoid static constructor convoy effect in parallel scenarios
    private static readonly Lazy<ImmutableArray<string>> _names = new (
                                                                       NamesValueFactory,
                                                                       LazyThreadSafetyMode.PublicationOnly);

    private static ImmutableArray<string> NamesValueFactory ()
    {
        string [] standardNames = Enum.GetNames<StandardColor> ().Order ().ToArray ();

        return [.. standardNames];
    }

    private static readonly Lazy<FrozenDictionary<uint, string>> _argbNameMap = new (
                                                                                     MapValueFactory,
                                                                                     LazyThreadSafetyMode.PublicationOnly);

    private static FrozenDictionary<uint, string> MapValueFactory ()
    {
        string [] standardNames = Enum.GetNames<StandardColor> ()
                                      .Order ()
                                      .ToArray ();
        Dictionary<uint, string> map = new (standardNames.Length);

        foreach (string name in standardNames)
        {
            var standardColor = Enum.Parse<StandardColor> (name);
            uint argb = GetArgb (standardColor);

            // TODO: Collect aliases?
            _ = map.TryAdd (argb, name);
        }

        return map.ToFrozenDictionary ();
    }

    /// <summary>
    ///     Gets read-only list of the W3C colors in alphabetical order.
    /// </summary>
    public static IReadOnlyList<string> GetColorNames () => _names.Value;

    /// <summary>
    ///     Converts the given Standard (W3C+) color name to equivalent color value.
    /// </summary>
    /// <param name="name">Standard (W3C+) color name.</param>
    /// <param name="color">The successfully converted Standard (W3C+) color value.</param>
    /// <returns>True if the conversion succeeded; otherwise false.</returns>
    public static bool TryParseColor (ReadOnlySpan<char> name, out Color color)
    {
        if (!Enum.TryParse (name, true, out StandardColor standardColor)
            ||

            // Any numerical value converts to undefined enum value.
            !Enum.IsDefined (standardColor))
        {
            color = default (Color);

            return false;
        }

        uint argb = GetArgb (standardColor);
        color = new (argb);

        return true;
    }

    /// <summary>
    ///     Converts the given color value to a Standard (W3C+) color name.
    /// </summary>
    /// <param name="color">Color value to match Standard (W3C+)color.</param>
    /// <param name="name">The successfully converted Standard (W3C+) color name.</param>
    /// <returns>True if conversion succeeded; otherwise false.</returns>
    public static bool TryNameColor (Color color, [NotNullWhen (true)] out string? name)
    {
        // Ignore alpha channel when matching - alpha represents transparency, not color identity
        uint opaqueArgb = color.Argb | 0xFF000000;

        if (_argbNameMap.Value.TryGetValue (opaqueArgb, out name))
        {
            return true;
        }

        name = null;

        return false;
    }

    internal static uint GetArgb (StandardColor standardColor)
    {
        const int ALPHA_SHIFT = 24;
        const uint ALPHA_MASK = 0xFFU << ALPHA_SHIFT;

        var rgb = (int)standardColor;

        uint argb = (uint)rgb | ALPHA_MASK;

        return argb;
    }
}