JsonNode.cs

namespace System.Runtime.Serialization.Json;
using System;
using System.Xml;
using System.Linq;
using System.Text;
using System.Xml.Linq;
using System.Collections;
using System.Collections.Generic;

public sealed class JsonNode :IEnumerable<JsonNode>
{
    enum _ { Null, Object, Array, String, Number, Boolean }

    readonly XElement Element;

    readonly _ Type;

    JsonNode(XElement _) => Enum.TryParse((Element = _).Attribute("type").Value, true, out Type);

    public static JsonNode Parse(string value)
    {
        using var _ = JsonReaderWriterFactory.CreateJsonReader(Encoding.Unicode.GetBytes(value), XmlDictionaryReaderQuotas.Max);
        return new(XElement.Load(_));
    }

    public JsonNode this[string key] => new(
        Type != _.Object
        ? throw new InvalidOperationException()
        : Element.Elements().First(_ => (_.Name.NamespaceName == string.Empty ? _.Name.LocalName : _.Attribute("item").Value) == key)
    );

    public JsonNode this[int index] => new(
        Type != _.Array
        ? throw new InvalidOperationException()
        : Element.Elements().ElementAt(index)
    );

    T Value<T>() => Type switch
    {
        JsonNode._.Null or JsonNode._.Object or JsonNode._.Array => throw new InvalidCastException(),
        _ => (T)Convert.ChangeType(Element.Value, typeof(T))
    };

    public double Number() => Value<double>();

    public string String() => Value<string>();

    public bool Boolean() => Value<bool>();

    public IEnumerator<JsonNode> GetEnumerator() => Element.Elements().Select(_ => new JsonNode(_)).GetEnumerator();

    IEnumerator IEnumerable.GetEnumerator() => null;
}