using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;
using System.Diagnostics.Contracts;
namespace APT.Infrastructure.Core
{
    public static class QueryableOrderExtension
    {
        public static IQueryable<T> SetQueryableOrder<T>(this IQueryable<T> query, string sort, string order, bool isThen = false)
        {
            if (string.IsNullOrEmpty(sort))
                throw new Exception("必须指定排序字段!");

            //PropertyInfo sortProperty = typeof(T).GetProperty(sort, BindingFlags.Public | BindingFlags.Instance | BindingFlags.IgnoreCase);
            //if (sortProperty == null)
            //    throw new Exception("查询对象中不存在排序字段" + sort + "！");

            ParameterExpression param = Expression.Parameter(typeof(T), "t");
            Expression body = param;
            if (Nullable.GetUnderlyingType(body.Type) != null)
                body = Expression.Property(body, "Value");
            body = GetPropertyLambdaExpression(body, sort);
            LambdaExpression keySelectorLambda = Expression.Lambda(body, param);

            if (string.IsNullOrEmpty(order))
                order = "ASC";
            string queryMethod = isThen ? order.ToUpper() == "DESC" ? "ThenByDescending" : "ThenBy" : order.ToUpper() == "DESC" ? "OrderByDescending" : "OrderBy";
            query = query.Provider.CreateQuery<T>(Expression.Call(typeof(Queryable), queryMethod,
                                                               new Type[] { typeof(T), body.Type },
                                                               query.Expression,
                                                               Expression.Quote(keySelectorLambda)));
            return query;
        }

        private static Expression GetPropertyLambdaExpression(Expression body, string fileName)
        {
            string[] propertyNames = fileName.Split('.');
            Type type = body.Type;
            foreach (string propertyName in propertyNames)
            {
                PropertyInfo property = type.GetProperty(propertyName);
                //Contract.Assume(property != null);
                if (property == null)
                {
                    throw new Exception($"类型{type.Name}不存在属性{propertyName}");
                }
                type = property.PropertyType;
                body = Expression.MakeMemberAccess(body, property);
            }
            return body;
        }
    }
}