using System.Linq.Expressions;
using System.Reflection;

namespace Tnb.Common.Utils
{
    public class DeepCopyHelper<T> where T : class, new() // 需要无参构造函数，构造表达式树的时候需要利用无参构造函数创建对象
    {
        /// <summary>
        /// 映射表达式，泛型缓存每个类型存一份
        /// </summary>
        private static readonly Func<T, T> s_CopyFunc = null;

        /// <summary>
        /// 静态构造函数，每个泛型类型会且只会执行一次
        /// </summary>
        static DeepCopyHelper()
        {
            BindingFlags bindingFlags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic;
            ParameterExpression parameterExpression = Expression.Parameter(typeof(T), "m"); // 参数m :m => 
            List<MemberBinding> memberBindingList = new List<MemberBinding>();
            foreach (var item in typeof(T).GetProperties(bindingFlags))
            {
                if (!item.CanWrite) // 只读属性不拷贝
                {
                    continue;
                }
                MemberExpression property = Expression.Property(parameterExpression, item); // m.Name
                MemberBinding memberBinding = Expression.Bind(item, property); // Name = m.Name
                memberBindingList.Add(memberBinding);
            }
            foreach (var item in typeof(T).GetFields(bindingFlags))
            {
                MemberExpression property = Expression.Field(parameterExpression, item);
                MemberBinding memberBinding = Expression.Bind(item, property);
                memberBindingList.Add(memberBinding);
            }
            MemberInitExpression memberInitExpression = Expression.MemberInit(Expression.New(typeof(T)), memberBindingList.ToArray());// new T() {Name = m.Name}
            Expression<Func<T, T>> lambda = Expression.Lambda<Func<T, T>>(memberInitExpression, new ParameterExpression[]
            {
                    parameterExpression
            }); // m => new T() {Name = m.Name}

            s_CopyFunc = lambda.Compile();
        }

        /// <summary>
        /// 对象拷贝（拷贝private/public：实例成员、属性、静态成员）
        /// </summary>
        /// <param name="data">源</param>
        /// <returns></returns>
        public static T DeepCopy(T data)
        {
            return s_CopyFunc(data);
        }

        /// <summary>
        /// 集合拷贝（拷贝private/public：实例成员、属性、静态成员）
        /// </summary>
        /// <param name="data">源</param>
        /// <returns></returns>
        public static List<T> DeepCopyList(List<T> data)
        {
            if (data == null || data.Count < 1)
            {
                return Enumerable.Empty<T>().ToList();
            }
            return data.Select(a => DeepCopy(a)).ToList();
        }
    }

}