using Nonemm.Core;

namespace Nonemm.Contests;

/// Time on and time off, which the sponsors of a contest with a rest rule ask
/// the entrant to declare. A gap between two contacts counts as time off when
/// it is at least the contest's `MinimumOffTime`; anything shorter is time
/// spent operating. This is how N1MM's off-time window reads a log.
public static class OperatingTime
{
    /// The gaps that count as time off, in the order they happened.
    public static IReadOnlyList<(DateTime From, DateTime To)> Breaks(
        IEnumerable<Qso> qsos,
        TimeSpan minimum)
    {
        List<(DateTime, DateTime)> found = [];
        DateTime? last = null;
        foreach (Qso qso in qsos.OrderBy(q => q.TimestampUtc))
        {
            if (last is { } before && qso.TimestampUtc - before >= minimum)
            {
                found.Add((before, qso.TimestampUtc));
            }
            last = qso.TimestampUtc;
        }
        return found;
    }

    public static TimeSpan Off(IEnumerable<Qso> qsos, TimeSpan minimum)
    {
        TimeSpan total = TimeSpan.Zero;
        foreach ((DateTime from, DateTime to) in Breaks(qsos, minimum))
        {
            total += to - from;
        }
        return total;
    }

    /// From the first contact to the last, less the time off. A log of one
    /// contact or none is no time at all.
    public static TimeSpan On(IEnumerable<Qso> qsos, TimeSpan minimum)
    {
        List<Qso> ordered = qsos.OrderBy(q => q.TimestampUtc).ToList();
        return ordered.Count < 2
            ? TimeSpan.Zero
            : ordered[^1].TimestampUtc - ordered[0].TimestampUtc - Off(ordered, minimum);
    }
}