using Nonemm.Core;

namespace Nonemm.Contests;

/// How fast contacts are being made, in contacts an hour. The network status
/// window shows two of these per station — over the last ten contacts and over
/// the last hundred — and the score window shows the same numbers for this
/// station.
public static class Rates
{
    /// Where N1MM stops dividing by a very short span. Under ten contacts the
    /// span counts as at least a minute, so three contacts in five seconds
    /// reads as 180 an hour rather than 2160.
    private const int ShortRun = 10;

    private static readonly TimeSpan Floor = TimeSpan.FromMinutes(1);

    /// The rate over the last `count` contacts before `nowUtc`.
    ///
    /// Counting stops at the first gap longer than `minimumOff`, so a rate
    /// after a night's rest is the rate since the operator came back rather
    /// than a hundred contacts spread over twelve hours. A log with no contact
    /// inside that gap is a rate of nothing.
    public static int PerHour(
        IEnumerable<Qso> qsos,
        int count,
        DateTime nowUtc,
        TimeSpan minimumOff)
    {
        DateTime oldest = nowUtc;
        int counted = 0;
        foreach (Qso qso in qsos.OrderByDescending(q => q.TimestampUtc).Take(count))
        {
            if (oldest - qso.TimestampUtc > minimumOff)
            {
                break;
            }
            oldest = qso.TimestampUtc;
            counted++;
        }
        if (counted == 0)
        {
            return 0;
        }
        TimeSpan span = nowUtc - oldest;
        if (counted < ShortRun && span < Floor)
        {
            span = Floor;
        }
        return span > TimeSpan.Zero
            ? (int)Math.Round(counted / span.TotalHours)
            : 0;
    }
}