using System;
using System.Linq;
using System.Threading.Tasks;
using Kendo.Mvc.Extensions;
using Kendo.Mvc.UI;
using System.Linq.Dynamic;
using System.Threading;
using System.Data.Entity;

namespace Test
{
    public class QueryTest
    {
        public async Task<DataSourceResult> GetPageAsync<T>(DataSourceRequest request, IQueryable<T> baseQuery,
            CancellationToken cancellationToken) where T : class, new()
        {
            var queryFiltered = baseQuery.Where(request.Filters);
            var sort = string.Empty;
            foreach (var sortDescriptor in request.Sorts)
            {
                if (string.IsNullOrWhiteSpace(sort))
                {
                    sort = sortDescriptor.Member + " " + sortDescriptor.SortDirection;
                }
                else
                {
                    sort += ", " + sortDescriptor.Member + " " + sortDescriptor.SortDirection;
                }
            }

            var query = !string.IsNullOrWhiteSpace(sort) ? queryFiltered.OrderBy(sort) : queryFiltered;

            // max of 5000 elements to reduce time for total count on large data
            int max = 5000;
            int totalItems = max;
            int take = request.PageSize;
            int skip = (request.Page - 1) * take;
            while (skip + 2 * take > totalItems)
            {
                totalItems += max;
            }

            var queryCount = queryFiltered.Cast<T>().Take(totalItems);
            var queryItems = query.Cast<T>().Skip(skip).Take(take);

            var items = await queryItems.ToListAsync(cancellationToken);
            var count = await queryCount.CountAsync(cancellationToken);

            var dsResult = new DataSourceResult()
            {
                Data = items,
                Total = count
            };

            return dsResult;
        }
    }
}