ADOFAIRenderer/Data/ColorJsonConverter.cs

using System;
using System.Globalization;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using UnityEngine;

namespace ADOFAIRenderer.Data;

/// <summary>
/// Converts Unity <see cref="Color"/> and nullable <see cref="Color"/> to and from hex string (#RRGGBBAA).
/// Pure C# implementation to completely avoid Unity internal native ECalls (such as Color.linear or ColorUtility.TryParseHtmlString).
/// </summary>
/// <remarks>
/// Reading accepts "#RRGGBB" (alpha 1), "#RRGGBBAA" (the '#' is optional), an object {"r","g","b","a"} with 0–1 floats
/// (missing r/g/b = 0, missing a = 1), or null. Invalid or unsupported input reads as null for Color? and as
/// default(Color) (all components 0) for Color; no exception is thrown for an unparsable string.
/// </remarks>
public class ColorJsonConverter : JsonConverter
{
    /// <summary>True for <see cref="Color"/> and <see cref="Nullable{Color}"/>.</summary>
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(Color) || objectType == typeof(Color?);
    }

    /// <summary>Writes the color as "#RRGGBBAA" (see <see cref="ToHex"/>), or a JSON null for a null value.</summary>
    public override void WriteJson(JsonWriter writer, object? value, JsonSerializer serializer)
    {
        if (value == null)
        {
            writer.WriteNull();
            return;
        }

        var color = (Color)value;
        writer.WriteValue(ToHex(color));
    }

    /// <summary>Reads a color in one of the accepted forms (see the class remarks).</summary>
    public override object? ReadJson(JsonReader reader, Type objectType, object? existingValue, JsonSerializer serializer)
    {
        bool isNullable = Nullable.GetUnderlyingType(objectType) != null || !objectType.IsValueType;

        if (reader.TokenType == JsonToken.Null)
        {
            return isNullable ? null : (object)default(Color);
        }

        if (reader.TokenType == JsonToken.String)
        {
            var str = (string?)reader.Value;
            if (TryParseHex(str, out var parsedColor))
            {
                return parsedColor;
            }

            return isNullable ? null : (object)default(Color);
        }

        if (reader.TokenType == JsonToken.StartObject)
        {
            var obj = JObject.Load(reader);
            float r = (float?)obj["r"] ?? 0f;
            float g = (float?)obj["g"] ?? 0f;
            float b = (float?)obj["b"] ?? 0f;
            float a = (float?)obj["a"] ?? 1f;
            return new Color(r, g, b, a);
        }

        return isNullable ? null : (object)default(Color);
    }

    /// <summary>
    /// Formats the color as "#RRGGBBAA" with uppercase hex digits. Each component is scaled to 0–255, rounded and clamped.
    /// The components are written as stored (no gamma conversion).
    /// </summary>
    public static string ToHex(Color color)
    {
        byte r = (byte)Math.Clamp((int)Math.Round(color.r * 255f), 0, 255);
        byte g = (byte)Math.Clamp((int)Math.Round(color.g * 255f), 0, 255);
        byte b = (byte)Math.Clamp((int)Math.Round(color.b * 255f), 0, 255);
        byte a = (byte)Math.Clamp((int)Math.Round(color.a * 255f), 0, 255);
        return $"#{r:X2}{g:X2}{b:X2}{a:X2}";
    }

    /// <summary>
    /// Parses "RRGGBB" or "RRGGBBAA" (optional leading '#', surrounding white space ignored, case-insensitive).
    /// </summary>
    /// <param name="hex">Text to parse.</param>
    /// <param name="color">Parsed color (components / 255; alpha 1 for the 6-digit form), or default when parsing fails.</param>
    /// <returns>True when the text was parsed.</returns>
    public static bool TryParseHex(string? hex, out Color color)
    {
        color = default;
        if (string.IsNullOrWhiteSpace(hex)) return false;

        var str = hex.Trim();
        if (str.StartsWith("#"))
        {
            str = str.Substring(1);
        }

        if (str.Length == 6)
        {
            if (byte.TryParse(str.Substring(0, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture, out var r) &&
                byte.TryParse(str.Substring(2, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture, out var g) &&
                byte.TryParse(str.Substring(4, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture, out var b))
            {
                color = new Color(r / 255f, g / 255f, b / 255f, 1f);
                return true;
            }
        }
        else if (str.Length == 8)
        {
            if (byte.TryParse(str.Substring(0, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture, out var r) &&
                byte.TryParse(str.Substring(2, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture, out var g) &&
                byte.TryParse(str.Substring(4, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture, out var b) &&
                byte.TryParse(str.Substring(6, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture, out var a))
            {
                color = new Color(r / 255f, g / 255f, b / 255f, a / 255f);
                return true;
            }
        }

        return false;
    }
}