Nonemm/src/Nonemm.Session/QtcTraffic.cs

using Nonemm.Contests;
using Nonemm.Contests.Rules;
using Nonemm.Core;

namespace Nonemm.Session;

/// Which way QTC traffic goes with a station, if it goes at all.
public enum QtcDirection
{
    None,
    Send,
    Receive,

    /// RTTY, where traffic goes both ways and the operator picks.
    Either,
}

/// The WAE QTC rules that do not need a window: who may exchange traffic with
/// whom, which contacts are still worth reporting, how the series are numbered,
/// and whether a line an operator has typed reads as a QTC.
///
/// On CW and SSB, traffic goes one way only: the station outside Europe reports
/// its contacts to the European station. On RTTY it goes both ways, and the
/// only rule left is that the two stations are on different continents.
public sealed class QtcTraffic
{
    private readonly RadioPosition position;

    public QtcTraffic(RadioPosition position) => this.position = position;

    public bool IsWaeContest => position.Contest is Wae;

    /// Which way traffic would go with this station. `reason` says why not when
    /// the answer is `None`, in the words the status line shows.
    public QtcDirection DirectionFor(Callsign other, out string reason)
    {
        reason = "";
        if (position.Contest is not Wae contest)
        {
            reason = "QTC traffic is a WAE thing";
            return QtcDirection.None;
        }
        if (other.Text.Length < 3)
        {
            reason = "work a station first";
            return QtcDirection.None;
        }
        if (Remaining(other) <= 0)
        {
            reason = $"{other.Text} has had its ten QTCs";
            return QtcDirection.None;
        }
        string theirs = ContinentOf(other);
        bool sameContinent = theirs.Length > 0 && theirs == position.Me.Continent;
        if (contest.Modes.Contains(ModeCategory.Digital))
        {
            if (sameContinent)
            {
                reason = $"{other.Text} is on this continent";
                return QtcDirection.None;
            }
            return QtcDirection.Either;
        }
        if (position.Me.Continent == "EU")
        {
            if (theirs == "EU")
            {
                reason = $"{other.Text} is in Europe";
                return QtcDirection.None;
            }
            return QtcDirection.Receive;
        }
        if (theirs != "EU")
        {
            reason = $"{other.Text} is not in Europe";
            return QtcDirection.None;
        }
        return QtcDirection.Send;
    }

    /// How many QTC lines have already gone either way with this station. Ten
    /// is the lot, for the whole contest and whatever the band.
    public int ExchangedWith(Callsign other) =>
        position.Log.Qsos.Count(q =>
            WaeQtc.IsQtc(q) && q.Call.Text.Equals(other.Text, StringComparison.OrdinalIgnoreCase));

    public int Remaining(Callsign other) =>
        Math.Max(0, WaeQtc.MostPerStation - ExchangedWith(other));

    /// Series are numbered across the whole contest, not per station: the
    /// hundredth series a station sends is `100/10` whoever gets it.
    public int NextSeries()
    {
        int last = position.Log.Qsos
            .Where(q => q.Exchange1.Equals(WaeQtc.Sent, StringComparison.OrdinalIgnoreCase))
            .Select(q => WaeQtc.From(q)?.Series ?? 0)
            .DefaultIfEmpty(0)
            .Max();
        return last + 1;
    }

    /// The contacts to report to this station: the ones not reported to anybody
    /// yet, oldest first, and never the station itself. Ten at a time unless
    /// the operator asks for a shorter series, and fewer when the station has
    /// already had some.
    public IReadOnlyList<WaeQtc> ToSend(Callsign other, int mostPerSeries = WaeQtc.MostPerSeries)
    {
        int room = Math.Min(Math.Clamp(mostPerSeries, 1, WaeQtc.MostPerSeries), Remaining(other));
        if (room <= 0)
        {
            return [];
        }
        HashSet<string> reported = position.Log.Qsos
            .Where(q => q.Exchange1.Equals(WaeQtc.Sent, StringComparison.OrdinalIgnoreCase))
            .Select(q => ReportedKey(q.ReceivedReport, q.ReceivedNumber))
            .ToHashSet(StringComparer.OrdinalIgnoreCase);
        List<Qso> worth = position.Log.Qsos
            .Where(q => !WaeQtc.IsQtc(q))
            .Where(q => !q.Call.Text.Equals(other.Text, StringComparison.OrdinalIgnoreCase))
            .Where(q => !reported.Contains(ReportedKey(q.Call.Text, q.SentNumber)))
            .OrderBy(q => q.TimestampUtc)
            .Take(room)
            .ToList();
        int series = NextSeries();
        return [.. worth.Select(q => new WaeQtc(
            other,
            IsSent: true,
            series,
            worth.Count,
            q.TimestampUtc.ToString("HHmm"),
            q.Call,
            q.ReceivedNumber,
            q.SentNumber))];
    }

    /// What the operator has typed, read as a QTC. Null when a field is empty
    /// or malformed, which is what the window paints yellow.
    public static WaeQtc? Read(
        Callsign station,
        bool isSent,
        int series,
        int countInSeries,
        string time,
        string call,
        string number)
    {
        string trimmedTime = time.Trim();
        string trimmedCall = call.Trim().ToUpperInvariant();
        if (trimmedTime.Length != 4
            || !trimmedTime.All(char.IsAsciiDigit)
            || !IsClockTime(trimmedTime)
            || trimmedCall.Length < 3
            || !int.TryParse(number.Trim(), out int parsed)
            || parsed <= 0)
        {
            return null;
        }
        return new WaeQtc(
            station, isSent, series, countInSeries, trimmedTime, Callsign.Parse(trimmedCall), parsed);
    }

    /// The header a station sends in front of a series: a series number, a
    /// separator and how many lines follow. Anything between the two numbers
    /// counts as the separator, because it is copied off the air.
    public static (int Series, int Count)? ReadHeader(string text)
    {
        string[] parts = text.Trim().ToUpperInvariant().Replace("QTC", "").Trim()
            .Split(['/', '-', ' ', '\\'], StringSplitOptions.RemoveEmptyEntries);
        return parts.Length >= 2
            && int.TryParse(parts[0], out int series)
            && int.TryParse(parts[1], out int count)
            && series > 0
            && count is > 0 and <= WaeQtc.MostPerSeries
            ? (series, count)
            : null;
    }

    private static bool IsClockTime(string text) =>
        int.Parse(text[..2]) < 24 && int.Parse(text[2..]) < 60;

    private static string ReportedKey(string call, int number) => $"{call}|{number}";

    private string ContinentOf(Callsign call) =>
        position.Session.Countries?.Find(call)?.Continent ?? "";
}