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src/__Libraries/StellaOps.Facet/Serialization/FacetSealJsonConverter.cs

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+// <copyright file="FacetSealJsonConverter.cs" company="StellaOps">
+// Copyright (c) StellaOps. Licensed under AGPL-3.0-or-later.
+// </copyright>
+
+using System.Collections.Immutable;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace StellaOps.Facet.Serialization;
+
+/// <summary>
+/// JSON serialization options for facet seals.
+/// </summary>
+public static class FacetJsonOptions
+{
+    /// <summary>
+    /// Gets the default JSON serializer options for facet seals.
+    /// </summary>
+    public static JsonSerializerOptions Default { get; } = CreateOptions();
+
+    /// <summary>
+    /// Gets options for compact serialization (no indentation).
+    /// </summary>
+    public static JsonSerializerOptions Compact { get; } = CreateOptions(writeIndented: false);
+
+    /// <summary>
+    /// Gets options for pretty-printed serialization.
+    /// </summary>
+    public static JsonSerializerOptions Pretty { get; } = CreateOptions(writeIndented: true);
+
+    private static JsonSerializerOptions CreateOptions(bool writeIndented = false)
+    {
+        var options = new JsonSerializerOptions
+        {
+            WriteIndented = writeIndented,
+            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+            PropertyNameCaseInsensitive = true
+        };
+
+        options.Converters.Add(new JsonStringEnumConverter(JsonNamingPolicy.CamelCase));
+        options.Converters.Add(new ImmutableArrayConverterFactory());
+        options.Converters.Add(new ImmutableDictionaryConverterFactory());
+
+        return options;
+    }
+}
+
+/// <summary>
+/// Converter factory for ImmutableArray{T}.
+/// </summary>
+internal sealed class ImmutableArrayConverterFactory : JsonConverterFactory
+{
+    public override bool CanConvert(Type typeToConvert)
+    {
+        return typeToConvert.IsGenericType &&
+               typeToConvert.GetGenericTypeDefinition() == typeof(ImmutableArray<>);
+    }
+
+    public override JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options)
+    {
+        var elementType = typeToConvert.GetGenericArguments()[0];
+        var converterType = typeof(ImmutableArrayConverter<>).MakeGenericType(elementType);
+        return (JsonConverter)Activator.CreateInstance(converterType)!;
+    }
+}
+
+/// <summary>
+/// Converter for ImmutableArray{T}.
+/// </summary>
+internal sealed class ImmutableArrayConverter<T> : JsonConverter<ImmutableArray<T>>
+{
+    public override ImmutableArray<T> Read(
+        ref Utf8JsonReader reader,
+        Type typeToConvert,
+        JsonSerializerOptions options)
+    {
+        if (reader.TokenType == JsonTokenType.Null)
+        {
+            return [];
+        }
+
+        var list = JsonSerializer.Deserialize<List<T>>(ref reader, options);
+        return list is null ? [] : [.. list];
+    }
+
+    public override void Write(
+        Utf8JsonWriter writer,
+        ImmutableArray<T> value,
+        JsonSerializerOptions options)
+    {
+        JsonSerializer.Serialize(writer, value.AsEnumerable(), options);
+    }
+}
+
+/// <summary>
+/// Converter factory for ImmutableDictionary{TKey,TValue}.
+/// </summary>
+internal sealed class ImmutableDictionaryConverterFactory : JsonConverterFactory
+{
+    public override bool CanConvert(Type typeToConvert)
+    {
+        return typeToConvert.IsGenericType &&
+               typeToConvert.GetGenericTypeDefinition() == typeof(ImmutableDictionary<,>);
+    }
+
+    public override JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options)
+    {
+        var keyType = typeToConvert.GetGenericArguments()[0];
+        var valueType = typeToConvert.GetGenericArguments()[1];
+        var converterType = typeof(ImmutableDictionaryConverter<,>).MakeGenericType(keyType, valueType);
+        return (JsonConverter)Activator.CreateInstance(converterType)!;
+    }
+}
+
+/// <summary>
+/// Converter for ImmutableDictionary{TKey,TValue}.
+/// </summary>
+internal sealed class ImmutableDictionaryConverter<TKey, TValue> : JsonConverter<ImmutableDictionary<TKey, TValue>>
+    where TKey : notnull
+{
+    public override ImmutableDictionary<TKey, TValue>? Read(
+        ref Utf8JsonReader reader,
+        Type typeToConvert,
+        JsonSerializerOptions options)
+    {
+        if (reader.TokenType == JsonTokenType.Null)
+        {
+            return null;
+        }
+
+        var dict = JsonSerializer.Deserialize<Dictionary<TKey, TValue>>(ref reader, options);
+        return dict?.ToImmutableDictionary();
+    }
+
+    public override void Write(
+        Utf8JsonWriter writer,
+        ImmutableDictionary<TKey, TValue> value,
+        JsonSerializerOptions options)
+    {
+        JsonSerializer.Serialize(writer, value.AsEnumerable().ToDictionary(kv => kv.Key, kv => kv.Value), options);
+    }
+}