public static IEnumerable<CampaignScheduleTaskInfo> GetGroupedPlayListItemsInRange(TimeLineResolution resolution, List<PlaylistItem> campaignPlaylistItems, DateTime startPosition, DateTime endPosition, uint maxInstances)
        {
            // Perform a sweep algorithm to find all playlistitems from all campaigns, where items from campaigns with lower index cover the ones with higher index

            // This array contains pointers for each campaign to the next playlist item after the current date time
            var data = new IEnumerator<CampaignScheduleTaskInfo>[campaignPlaylistItems.Count];
            int i = 0;
            foreach (var campaignPlaylistItem in from c in campaignPlaylistItems orderby c.Priority ascending select c)
            {
                data[i++] = GetGroupedPlayListItemsInRange(resolution, campaignPlaylistItem, startPosition, endPosition, maxInstances).GetEnumerator();
            }

            // Create initial sweep jobs
            i = 0;
            var sweepJobs = new List<SweepStatus>();
            foreach (var campaign in data)
            {
                CreateNewSweepJob(campaign, i++, ref sweepJobs);
            }

            // Do the sweep algorithm: one job at a time, from left to right
            SweepStatus status = null;
            while (sweepJobs.Count != 0)
            {
                var currentJob = (from x in sweepJobs orderby x.Position select x).FirstOrDefault();
                sweepJobs.Remove(currentJob);

                if (status == null)
                {
                    status = currentJob;
                    continue;
                }

                if (currentJob.StartPoint) // Job starts
                {
                    if (currentJob.Index < status.Index) // Higher priority job starts, emit result
                    {
                        status.CampaignInfo.EndTime = currentJob.CampaignInfo.StartTime;
                        yield return status.CampaignInfo;
                        status = currentJob;
                    }
                    else // Lower priority job starts, ignore
                    {

                    }
                }
                else // Job ends
                {
                    if (currentJob.Index > status.Index) // Lower priority job ends, increment enumerator and create new sweep jobs
                    {
                        CreateNewSweepJob(data[currentJob.Index], currentJob.Index, ref sweepJobs);
                    }
                    else // Higher priority job ends
                    {
                        yield return status.CampaignInfo;

                        i = 0;
                        bool found = false;
                        foreach (var campaign in data)
                        {
                            if (campaign.Current.StartTime <= currentJob.Position && campaign.Current.EndTime >= currentJob.Position)
                            {
                                status = new SweepStatus()
                                {
                                    Position = currentJob.Position,
                                    StartPoint = true,
                                    Index = i,
                                    CampaignInfo = campaign.Current
                                };
                                found = true;
                                break;
                            }
                            ++i;
                        }
                        if (!found)
                            status = null;
                    }
                }
            }
        }