using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;

namespace DS.Module.Core.Extensions
{
    public static class EnumExtensions
    {
        // 枚举显示字典缓存
        private static readonly ConcurrentDictionary<Type, Dictionary<string, string>> EnumDisplayValueDict = new();

        // 枚举值字典缓存
        private static readonly ConcurrentDictionary<Type, Dictionary<string, string>> EnumNameValueDict = new();

        // 枚举类型缓存
        private static ConcurrentDictionary<string, Type> _enumTypeDict = null;

        /// <summary>
        /// 获取枚举类型key与描述的字典（缓存）
        /// </summary>
        /// <param name="enumType"></param>
        /// <returns></returns>
        /// <exception cref="Exception"></exception>
        public static Dictionary<string, string> GetEnumDescDictionary(Type enumType)
        {
            if (!enumType.IsEnum)
                throw new Exception("该类型不是枚举类型");

            // 查询缓存
            Dictionary<string, string> enumDic = EnumDisplayValueDict.ContainsKey(enumType) ? EnumDisplayValueDict[enumType] : new Dictionary<string, string>();
            if (enumDic.Count == 0)
            {
                // 取枚举类型的Key/Value字典集合
                enumDic = GetEnumDescDictionaryItems(enumType);

                // 缓存
                EnumDisplayValueDict[enumType] = enumDic;
            }
            return enumDic;
        }

        /// <summary>
        /// 获取枚举类型key与描述的字典（没有描述则获取name）
        /// </summary>
        /// <param name="enumType"></param>
        /// <returns></returns>
        /// <exception cref="Exception"></exception>
        private static Dictionary<string, string> GetEnumDescDictionaryItems(Type enumType)
        {
            // 获取类型的字段，初始化一个有限长度的字典
            FieldInfo[] enumFields = enumType.GetFields(BindingFlags.Public | BindingFlags.Static);
            Dictionary<string, string> enumDic = new(enumFields.Length);

            // 遍历字段数组获取key和name
            foreach (FieldInfo enumField in enumFields)
            {
                string fileValue = enumField.Name;
                var desc = enumField.GetDescriptionValue<DescriptionAttribute>();
                enumDic[fileValue] = desc != null && !string.IsNullOrEmpty(desc.Description) ? desc.Description : enumField.Name;
            }
            return enumDic;
        }

        /// <summary>
        /// 获取字段特性
        /// </summary>
        /// <param name="field"></param>
        /// <typeparam name="T"></typeparam>
        /// <returns></returns>
        public static T GetDescriptionValue<T>(this FieldInfo field) where T : Attribute
        {
            // 获取字段的指定特性，不包含继承中的特性
            object[] customAttributes = field.GetCustomAttributes(typeof(T), false);

            // 如果没有数据返回null
            return customAttributes.Length > 0 ? (T)customAttributes[0] : null;
        }
    }
}