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

namespace Kreta.BusinessLogic.HelperClasses.OsztalyCsoportbaSorolas
{
    public static class BesorolasDateRangeUtil
    {
        public static BesorolasOverlapResult CalculateMaxOverlap(DateTime besorolasKezdete, DateTime besorolasVege, IEnumerable<BesorolasDateRange> besorolasok)
        {
            var maxOverlapCount = 0;
            DateTime? maxOverlapBeginDate = null;
            int? maxOverlapOsztalyId = null;

            var dateList = CreateDateList(besorolasKezdete, besorolasVege);
            foreach (var date in dateList)
            {
                var overlappedRanges = GetOverlappedRanges(date, besorolasok);
                var overlapCount = overlappedRanges.Count();
                if (overlapCount > maxOverlapCount)
                {
                    maxOverlapCount = overlapCount;
                    maxOverlapBeginDate = date;
                    var overlappedBesorolas = overlappedRanges.FirstOrDefault(x => x.OsztalyCsoportId.HasValue);
                    if (overlappedBesorolas != null)
                    {
                        maxOverlapOsztalyId = overlappedBesorolas.OsztalyCsoportId.Value;
                    }
                }
            }

            return new BesorolasOverlapResult(maxOverlapCount, maxOverlapBeginDate, maxOverlapOsztalyId);
        }

        public static BesorolasOverlapResult CalculateMinOverlap(DateTime besorolasKezdete, DateTime besorolasVege, IEnumerable<BesorolasDateRange> besorolasok)
        {
            var minOverlapCount = int.MaxValue;
            DateTime? minOverlapBeginDate = null;

            var dateList = CreateDateList(besorolasKezdete, besorolasVege);
            foreach (var date in dateList)
            {
                var overlappedRanges = GetOverlappedRanges(date, besorolasok);
                var overlapCount = overlappedRanges.Count();
                if (overlapCount < minOverlapCount)
                {
                    minOverlapCount = overlapCount;
                    minOverlapBeginDate = date;
                }
            }

            return new BesorolasOverlapResult(minOverlapCount, minOverlapBeginDate);
        }

        private static IEnumerable<DateTime> CreateDateList(DateTime begin, DateTime end)
        {
            return Enumerable.Range(0, end.Subtract(begin).Days).Select(d => begin.AddDays(d));
        }

        private static IEnumerable<BesorolasDateRange> GetOverlappedRanges(DateTime examinedDate, IEnumerable<BesorolasDateRange> ranges)
        {
            // NOTE: Ha egyszer a besorolás jobbról is zárt lesz, akkor az End-nél egyenlőséget is kell vizsgálni.
            return ranges.Where(r => r.Begin <= examinedDate && r.End > examinedDate);
        }
    }

    public class BesorolasDateRange
    {
        public DateTime Begin { get; set; }

        public DateTime End { get; set; }

        public int? OsztalyCsoportId { get; set; }
    }

    public class BesorolasOverlapResult
    {
        public int OverlapCount { get; private set; }

        public DateTime? OverlapBeginDate { get; private set; }

        public int? MaxOverlapOsztalyId { get; private set; }

        public BesorolasOverlapResult(int overlapCount, DateTime? overlapBeginDate)
        {
            OverlapCount = overlapCount;
            OverlapBeginDate = overlapBeginDate;
        }

        public BesorolasOverlapResult(int overlapCount, DateTime? overlapBeginDate, int? maxOverlapOsztalyId)
        {
            OverlapCount = overlapCount;
            OverlapBeginDate = overlapBeginDate;
            MaxOverlapOsztalyId = maxOverlapOsztalyId;
        }
    }
}