public double MinutesAbsent(IEnumerable <Presence> presences)
{
// Given a list of presences, select only those that overlap this block
var relevantPresences = Presence.CombineOverlapping(
presences?.Where(p => p?.OverlapsWith(this) == true))?
.OrderBy(p => p.Arrival)
.ToList();
// If there aren't any relevant presences, return the total minutes for this block
if (relevantPresences == null || relevantPresences.Count == 0)
{
return((End - Start).TotalMinutes);
}
// Get any absent minutes at the start of the block by determining
// if the first presence arrived after the block's start. If it did,
// begin with the difference between the block's Start and the
// first presence's Arrival.
var minutesAbsent = relevantPresences.First().Arrival > Start
? (relevantPresences.First().Arrival - Start).TotalMinutes
: 0;
// Then add the number of minutes between each presence's
// Departure and the next presence's Arrival
for (var i = 0; i < relevantPresences.Count - 1; i++)
{
minutesAbsent += (relevantPresences[i + 1].Arrival -
relevantPresences[i].Departure).TotalMinutes;
}
// Finally, add any minutes after the last presence
// if it departed before the end of the block
if (relevantPresences.Last().Departure < End)
{
minutesAbsent += (End - relevantPresences.Last().Departure).TotalMinutes;
}
return(minutesAbsent);
}
