using System;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;

namespace StardewModdingAPI.Toolkit.Serialization.Converters
{
    /// <summary>The base implementation for simplified converters which deserialize <typeparamref name="T"/> without overriding serialization.</summary>
    /// <typeparam name="T">The type to deserialize.</typeparam>
    internal abstract class SimpleReadOnlyConverter<T> : JsonConverter
    {
        /*********
        ** Accessors
        *********/
        /// <summary>Whether this converter can write JSON.</summary>
        public override bool CanWrite => false;


        /*********
        ** Public methods
        *********/
        /// <summary>Get whether this instance can convert the specified object type.</summary>
        /// <param name="objectType">The object type.</param>
        public override bool CanConvert(Type objectType)
        {
            return objectType == typeof(T) || Nullable.GetUnderlyingType(objectType) == typeof(T);
        }

        /// <summary>Reads the JSON representation of the object.</summary>
        /// <param name="reader">The JSON reader.</param>
        /// <param name="objectType">The object type.</param>
        /// <param name="existingValue">The object being read.</param>
        /// <param name="serializer">The calling serializer.</param>
        public override object? ReadJson(JsonReader reader, Type objectType, object? existingValue, JsonSerializer serializer)
        {
            string path = reader.Path;
            switch (reader.TokenType)
            {
                case JsonToken.Null when Nullable.GetUnderlyingType(objectType) != null:
                    return null;

                case JsonToken.StartObject:
                    return this.ReadObject(JObject.Load(reader), path);

                case JsonToken.String:
                    return this.ReadString(JToken.Load(reader).Value<string>(), path);

                default:
                    throw new SParseException($"Can't parse {typeof(T).Name} from {reader.TokenType} node (path: {reader.Path}).");
            }
        }

        /// <summary>Writes the JSON representation of the object.</summary>
        /// <param name="writer">The JSON writer.</param>
        /// <param name="value">The value.</param>
        /// <param name="serializer">The calling serializer.</param>
        public override void WriteJson(JsonWriter writer, object? value, JsonSerializer serializer)
        {
            throw new InvalidOperationException("This converter does not write JSON.");
        }


        /*********
        ** Protected methods
        *********/
        /// <summary>Read a JSON object.</summary>
        /// <param name="obj">The JSON object to read.</param>
        /// <param name="path">The path to the current JSON node.</param>
        protected virtual T ReadObject(JObject obj, string path)
        {
            throw new SParseException($"Can't parse {typeof(T).Name} from object node (path: {path}).");
        }

        /// <summary>Read a JSON string.</summary>
        /// <param name="str">The JSON string value.</param>
        /// <param name="path">The path to the current JSON node.</param>
        protected virtual T ReadString(string str, string path)
        {
            throw new SParseException($"Can't parse {typeof(T).Name} from string node (path: {path}).");
        }
    }
}