MonoGame.Extended/source/MonoGame.Extended/Serialization/NinePatchRegion2DJsonConverter.cs

using System;
using System.Text.Json;
using System.Text.Json.Serialization;
using MonoGame.Extended.TextureAtlases;

namespace MonoGame.Extended.Serialization;

/// <summary>
/// Converts a <see cref="NinePatchRegion2D"/> value to or from JSON.
/// </summary>
public class NinePatchRegion2DJsonConverter : JsonConverter<NinePatchRegion2D>
{
    private readonly ITextureRegionService _textureRegionService;

    /// <summary>
    /// Initializes a new instance of the <see cref="NinePatchRegion2DJsonConverter"/> class.
    /// </summary>
    /// <param name="textureRegionService">The texture region service used to retrieve texture regions.</param>
    public NinePatchRegion2DJsonConverter(ITextureRegionService textureRegionService)
    {
        _textureRegionService = textureRegionService;
    }

    /// <inheritdoc />
    public override bool CanConvert(Type typeToConvert) => typeToConvert == typeof(NinePatchRegion2D);

    /// <inheritdoc />
    /// <exception cref="JsonException">
    /// Thrown if the JSON property does not contain a properly formatted <see cref="NinePatchRegion2D"/> value
    /// </exception>
    public override NinePatchRegion2D Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (reader.TokenType != JsonTokenType.StartObject)
        {
            throw new JsonException($"Expected {nameof(JsonTokenType.StartObject)} token");
        }

        string padding = string.Empty;
        string regionName = string.Empty;

        while (reader.Read())
        {
            if (reader.TokenType == JsonTokenType.EndObject)
            {
                break;
            }

            if (reader.TokenType == JsonTokenType.PropertyName)
            {
                var propertyName = reader.GetString();
                reader.Read();

                if (propertyName.Equals("Padding", StringComparison.Ordinal))
                {
                    padding = reader.GetString();
                }
                else if (propertyName.Equals("TextureRegion", StringComparison.Ordinal))
                {
                    regionName = reader.GetString();
                }
            }
        }

        if (string.IsNullOrEmpty(padding) || string.IsNullOrEmpty(regionName))
        {
            throw new JsonException($"Missing required properties \"Padding\" and \"TextureRegion\"");
        }

        var thickness = Thickness.Parse(padding);
        var region = _textureRegionService.GetTextureRegion(regionName);

        return new NinePatchRegion2D(region, thickness.Left, thickness.Top, thickness.Right, thickness.Bottom);
    }

    /// <inheritdoc />
    /// <exception cref="ArgumentNullException">
    /// Throw if <paramref name="writer"/> is <see langword="null"/>.
    /// </exception>
    public override void Write(Utf8JsonWriter writer, NinePatchRegion2D value, JsonSerializerOptions options)
    {
        ArgumentNullException.ThrowIfNull(writer);

        if (value is null)
        {
            writer.WriteNullValue();
            return;
        }

        writer.WriteStartObject();
        writer.WriteString("TextureRegion", value.Name);
        writer.WriteString("Padding", value.Padding.ToString());
        writer.WriteEndObject();
    }
}