MLEM/MLEM.Data/Json/JsonTypeSafeWrapper.cs

using System;
using System.Collections.Generic;
using System.Runtime.Serialization;
using Newtonsoft.Json;

namespace MLEM.Data.Json {
    /// <summary>
    /// A json type-safe wrapper can be used to wrap any objects of any type before submitting them to a non-specifically typed <see cref="List{T}"/> or <see cref="Dictionary{T,T}"/> that will be serialized using a <see cref="JsonSerializer"/> in cases where <see cref="JsonSerializer.TypeNameHandling"/> is not set to <see cref="TypeNameHandling.None"/>.
    /// If any object is not wrapped in this manner, and it has a custom <see cref="JsonConverter"/>, the value deserialized from it might not have the same type as the originally serialized object. This behavior can be observed, for example, when serializing a <see cref="List{T}"/> of <see cref="object"/> entries, one of which is a <see cref="TimeSpan"/>: The <see cref="TimeSpan"/> will be serialized as a <see cref="string"/> and, upon deserialization, will remain a <see cref="string"/>.
    /// In general, wrapping objects in this manner is only useful in rare cases, where custom data of an unexpected or unknown type is stored.
    /// See <see cref="JsonTypeSafeGenericDataHolder"/> for an example of how this class can be used, and see this stackoverflow answer for more information on the problem that this class solves: https://stackoverflow.com/a/38798114.
    /// </summary>
    public abstract class JsonTypeSafeWrapper {

        /// <summary>
        /// Returns this json type-safe wrapper's value as an <see cref="object"/>.
        /// </summary>
        public abstract object Value { get; }

        /// <summary>
        /// Returns the current <see cref="Value"/> of this <see cref="JsonTypeSafeWrapper"/>, typecast to the given type <typeparamref name="T"/>.
        /// If this <see cref="Value"/>'s type is incompatible with the given type, the type's default value is returned instead.
        /// </summary>
        /// <typeparam name="T">The type of value to return</typeparam>
        /// <returns>The <see cref="Value"/>, castt to the given type if compatible, otherwise default</returns>
        public T GetValue<T>() {
            return this.Value is T t ? t : default;
        }

        /// <summary>
        /// Creates a new <see cref="JsonTypeSafeWrapper{T}"/> from the given value.
        /// The type parameter of the returned wrapper will be equal to the <see cref="Type"/> of the <paramref name="value"/> passed.
        /// If a <see cref="JsonTypeSafeWrapper{T}"/> for a specific type, known at comepile type, should be created, you can use <see cref="JsonTypeSafeWrapper{T}(T)"/>.
        /// </summary>
        /// <param name="value">The value to wrap</param>
        /// <returns>A <see cref="JsonTypeSafeWrapper{T}"/> with a type matching the type of <paramref name="value"/></returns>
        public static JsonTypeSafeWrapper Of(object value) {
            var type = typeof(JsonTypeSafeWrapper<>).MakeGenericType(value.GetType());
            return (JsonTypeSafeWrapper) Activator.CreateInstance(type, value);
        }

    }

    /// <inheritdoc />
    [DataContract]
    public class JsonTypeSafeWrapper<T> : JsonTypeSafeWrapper {

        /// <inheritdoc />
        public override object Value => this.value;
        [DataMember]
        private readonly T value;

        /// <summary>
        /// Creates a new json type-safe wrapper instance that wraps the given <paramref name="value"/>.
        /// If the type of the value is unknown at compile time, <see cref="JsonTypeSafeWrapper.Of"/> can be used instead.
        /// </summary>
        /// <param name="value">The value to wrap</param>
        public JsonTypeSafeWrapper(T value) {
            this.value = value;
        }

    }
}