using System.Collections.Generic;
using System.Linq;
using System.Reflection;

using Microsoft.EntityFrameworkCore.Query;
using Microsoft.EntityFrameworkCore.Query.SqlExpressions;


namespace ASC.Core.Common.EF
{
    public static class IQueryableExtensions
    {
        public static string ToSql<TEntity>(this IQueryable<TEntity> query) where TEntity : class
        {
            var enumerator = query.Provider.Execute<IEnumerable<TEntity>>(query.Expression).GetEnumerator();
            var relationalCommandCache = enumerator.Private("_relationalCommandCache");
            var selectExpression = relationalCommandCache.Private<SelectExpression>("_selectExpression");
            var factory = relationalCommandCache.Private<IQuerySqlGeneratorFactory>("_querySqlGeneratorFactory");

            var sqlGenerator = factory.Create();
            var command = sqlGenerator.GetCommand(selectExpression);

            var sql = command.CommandText;
            return sql;
        }

        private static object Private(this object obj, string privateField)
        {
            return obj?.GetType().GetField(privateField, BindingFlags.Instance | BindingFlags.NonPublic)?.GetValue(obj);
        }

        private static T Private<T>(this object obj, string privateField)
        {
            return (T)obj?.GetType().GetField(privateField, BindingFlags.Instance | BindingFlags.NonPublic)?.GetValue(obj);
        }
    }
}