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

namespace YLErp.Helpers
{
    /// <summary>
    /// 合计帮助类
    /// </summary>
    public static class SumHelper
    {
        /// <summary>
        /// 属性合计
        /// </summary>
        public static Dictionary<string, object> CalculateSums<T>(IEnumerable<T> list) where T : class
        {
            var type = typeof(T);
            var sum = new Dictionary<string, object>();
            var properties = type.GetProperties(BindingFlags.Public | BindingFlags.Instance);
            foreach (var property in properties)
            {
                if (property.PropertyType != typeof(int) && property.PropertyType != typeof(long) &&
                    property.PropertyType != typeof(decimal) && property.PropertyType != typeof(double)
                    && property.PropertyType != typeof(int?) && property.PropertyType != typeof(long?) &&
                    property.PropertyType != typeof(decimal?) && property.PropertyType != typeof(double?))
                {
                    continue;
                }
                var parameter = Expression.Parameter(typeof(T), string.Empty);
                var source = Expression.Constant(list, typeof(IEnumerable<T>));
                var member = Expression.PropertyOrField(parameter, property.Name);
                var lambda = Expression.Lambda(member, parameter);
                var call = Expression.Call(
                    typeof(Enumerable),
                    "Sum",
                    new[] { type },
                    source,
                    lambda);
                sum[property.Name + "Sum"] = new List<int>().AsQueryable().Provider.Execute(call);
            }
            return sum;
        }
    }
}