using System;


namespace UniJSON
{
    struct GenericCast<S, T>
    {
        public static T Null()
        {
            if (typeof(T).IsClass)
            {
                return default(T);
            }
            else
            {
                throw new MsgPackTypeException("can not null");
            }
        }

        delegate T CastFunc(S value);
        static CastFunc s_cast;

        delegate Func<T> ConstFuncCreator(S value);
        static ConstFuncCreator s_const;

        public static Func<T> Const(S value)
        {
            if (s_const == null)
            {
                s_const = new ConstFuncCreator(GenericCast.CreateConst<S, T>());
            }
            return s_const(value);
        }

        public static T Cast(S value)
        {
            if (s_cast == null)
            {
                s_cast = new CastFunc(GenericCast.CreateCast<S, T>());
            }
            return s_cast(value);
        }
    }

    static partial class GenericCast
    {
        public static Func<S, T> CreateCast<S, T>()
        {
            var mi = ConcreteCast.GetMethod(typeof(S), typeof(T));
            if (mi == null)
            {
                return (Func<S, T>)((S s) =>
                {
                    return (T)(object)s;
                });
            }
            else
            {
                return (Func<S, T>)((S s) =>
                {
                    return (T)mi.Invoke(null, new object[] { s });
                });
            }
        }

        public static Func<S, Func<T>> CreateConst<S, T>()
        {
            var cast = CreateCast<S, T>();
            return (Func<S, Func<T>>)((S s) =>
            {
                return (Func<T>)(() => cast(s));
            });
        }
    }
}