using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Reflection;

namespace Church.Net.Utility
{
    public static class EnumHelper
    {

        public static string EnumToDescriptionString(this Enum val)
        {
            //pull out first value in case of flag enumeration
            var firstValue = val.ToString().Split(',').Select(s => s.Trim()).First();
            IEnumerable<DescriptionAttribute> attributes = val
               .GetType()
               .GetField(firstValue)
               .GetCustomAttributes<DescriptionAttribute>(false);
            return true == attributes?.Any() ? attributes.First().Description : val.ToString();
        }

        public static T GetEnumValueFromDescription<T>(string description) where T : struct
        {
            object value = GetEnumValueFromDescription(typeof(T), description);
            return value is null ? default : (T)value;
        }

        public static object GetEnumValueFromDescription(Type type, string description)
        {
            if (type is null) return null;
            if (!type.IsEnum)
            {
                if (type.IsNullableEnum())
                {
                    type = Nullable.GetUnderlyingType(type);
                }
                else
                {
                    throw new ArgumentException();
                }
            }

            FieldInfo field = type.GetFields()
                .FirstOrDefault(f => f.GetCustomAttributes<DescriptionAttribute>(false)
                    .FirstOrDefault(a => a.Description == description) != null
                )
            ;
            return field == null ? null : Enum.ToObject(type, field?.GetRawConstantValue());
            return field?.GetRawConstantValue();
        }

        public static bool IsNullableEnum(this Type t)
        {
            Type u = Nullable.GetUnderlyingType(t);
            return (u != null) && u.IsEnum;
        }
        public static TEnum GetDefaultEnumValue<TEnum>() where TEnum : struct
        {
            return (TEnum)GetDefaultEnumValue(typeof(TEnum));
        }

        public static object GetDefaultEnumValue(Type type)
        {
            if (type is null) return null;
            IEnumerable<DefaultValueAttribute> attributes = type.GetCustomAttributes<DefaultValueAttribute>(false);
            return attributes?.FirstOrDefault()?.Value;
        }
    }
}