using System;
using System.Collections.Generic;
using System.Linq.Expressions;

namespace Masuit.Tools.Core
{
    /// <summary>
    /// 生成表达式目录树  泛型缓存
    /// </summary>
    public static class ExpressionGenericMapper
    {
        private static object func;

        /// <summary>
        /// 高性能对象浅克隆映射
        /// </summary>
        /// <typeparam name="TSource"></typeparam>
        /// <typeparam name="TDestination"></typeparam>
        /// <param name="source"></param>
        /// <returns></returns>
        public static TDestination Map<TSource, TDestination>(this TSource source)
        {
            if (func is null) //如果表达式不存在，则走一遍编译过程
            {
                ParameterExpression parameterExpression = Expression.Parameter(typeof(TSource), "p");
                var memberBindingList = new List<MemberBinding>(); //表示绑定的类派生自的基类，这些绑定用于对新创建对象的成员进行初始化(vs的注解。太生涩了，我这样的小白解释不了，大家将就着看)
                foreach (var item in typeof(TDestination).GetProperties()) //遍历目标类型的所有属性
                {
                    MemberExpression property = Expression.Property(parameterExpression, typeof(TSource).GetProperty(item.Name)); //获取到对应的属性
                    MemberBinding memberBinding = Expression.Bind(item, property); //初始化这个属性
                    memberBindingList.Add(memberBinding);
                }

                foreach (var item in typeof(TDestination).GetFields())
                {
                    MemberExpression property = Expression.Field(parameterExpression, typeof(TSource).GetField(item.Name)); //获取到对应的字段
                    MemberBinding memberBinding = Expression.Bind(item, property); //同上
                    memberBindingList.Add(memberBinding);
                }

                MemberInitExpression memberInitExpression = Expression.MemberInit(Expression.New(typeof(TDestination)), memberBindingList.ToArray()); //初始化创建新对象
                Expression<Func<TSource, TDestination>> lambda = Expression.Lambda<Func<TSource, TDestination>>(memberInitExpression, parameterExpression);
                func = lambda.Compile();
            }

            if (source == null)
            {
                return default(TDestination);
            }

            return ((Func<TSource, TDestination>)func)(source); //拼装是一次性的
        }

        /// <summary>
        /// 集合映射
        /// </summary>
        /// <typeparam name="TSource"></typeparam>
        /// <typeparam name="TDestination"></typeparam>
        /// <param name="source"></param>
        /// <returns></returns>
        public static IEnumerable<TDestination> Map<TSource, TDestination>(this IEnumerable<TSource> source)
        {
            foreach (TSource s in source)
            {
                yield return s.Map<TSource, TDestination>();
            }
        }

        /// <summary>
        /// 集合映射
        /// </summary>
        /// <typeparam name="TSource"></typeparam>
        /// <typeparam name="TDestination"></typeparam>
        /// <param name="source"></param>
        /// <returns></returns>
        public static IEnumerable<TDestination> Map<TSource, TDestination>(this IList<TSource> source)
        {
            foreach (TSource s in source)
            {
                yield return s.Map<TSource, TDestination>();
            }
        }

        /// <summary>
        /// 集合映射
        /// </summary>
        /// <typeparam name="TSource"></typeparam>
        /// <typeparam name="TDestination"></typeparam>
        /// <param name="source"></param>
        /// <returns></returns>
        public static IEnumerable<TDestination> Map<TSource, TDestination>(this ICollection<TSource> source)
        {
            foreach (TSource s in source)
            {
                yield return s.Map<TSource, TDestination>();
            }
        }
    }
}