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

namespace linq_slideviews
{
    public class StatisticsTask
    {
        public static double GetMedianTimePerSlide(List<VisitRecord> visits, SlideType slideType)
        {
            return visits.OrderBy(visit => visit.DateTime)
                .GroupBy(visit => visit.UserId)
                .SelectMany(visit => visit.Bigrams())
                .Where(visit => visit.Item1.SlideType == slideType)
                .Select(visit => visit.Item1.DateTime - visit.Item2.DateTime)
                .Where(time => time >= TimeSpan.FromMinutes(1) && time <= TimeSpan.FromMinutes(120))
                .Select(time => time.TotalMinutes)
                .DefaultIfEmpty(0)
                .Median();
        }
    }
}