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

namespace WorkerService.Process
{
    /// <summary>
    /// Function JSON converter
    /// </summary>
    /// <typeparam name="TParameter">Function input type</typeparam>
    /// <typeparam name="TOutput">Function output type</typeparam>
    public class FunctionConverter<TParameter, TOutput> : JsonConverter
    {
        /// <summary>
        /// Writes the JSON representation of the object
        /// </summary>
        /// <param name="writer">The JsonWriter to write to</param>
        /// <param name="value">The value to write</param>
        /// <param name="serializer">The calling serializer</param>
        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            if (value is Func<TParameter, TOutput> function)
            {
                writer.WriteValue($"{function.Method.DeclaringType}.{function.Method.Name}");
            }
        }

        /// <summary>Reads the JSON representation of the object.</summary>
        /// <param name="reader">JsonReader to read from</param>
        /// <param name="objectType">Type of the object</param>
        /// <param name="existingValue">The existing value of object being read</param>
        /// <param name="serializer">The calling serializer</param>
        /// <returns>The object value</returns>
        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            //Get the function's full path
            string fullFunctionPath = (string)reader.Value;
            if (string.IsNullOrEmpty(fullFunctionPath))
            {
                return null;
            }

            //Extract class and function names
            string className = fullFunctionPath.Substring(0, fullFunctionPath.LastIndexOf(".", StringComparison.Ordinal));
            string functionName = fullFunctionPath.Substring(fullFunctionPath.LastIndexOf(".", StringComparison.Ordinal) + 1);

            //Get the class type
            Type classType = AppDomain.CurrentDomain.GetAssemblies().SelectMany(a => a.GetTypes()).FirstOrDefault(t => string.Equals(t.FullName, className, StringComparison.CurrentCultureIgnoreCase));
            if (classType == null)
            {
                return null;
            }

            //Get the function's method info
            MethodInfo methodInfo = classType.GetMethod(functionName);
            if (methodInfo == null)
            {
                return null;
            }

            return (Func<TParameter, TOutput>)methodInfo.CreateDelegate(typeof(Func<TParameter, TOutput>));
        }

        /// <summary>
        /// Determines whether this instance can convert the specified object type
        /// </summary>
        /// <param name="objectType">Type of the object</param>
        /// <returns>
        /// Whether or not this instance can convert ot the specified object type
        /// </returns>
        public override bool CanConvert(Type objectType)
        {
            return objectType == typeof(Func<TParameter, TOutput>);
        }
    }
}