using Nonemm.Core;

namespace Nonemm.Contests;

/// One station of the entry with its key down, as the others see it.
public sealed record Transmitter(string ComputerName, Band? Band, ModeCategory? Mode);

/// How many signals a multi-operator entry may have on the air at once, and on
/// which bands.
///
/// N1MM blocks the transmitter when the entry is about to break these. This
/// program does not touch the transmitter — a logger that decides for itself
/// when the operator may not send is a logger that loses a contact when it is
/// wrong — so it says what is happening and leaves it to the operator.
///
/// | Entry | What is allowed |
/// |---|---|
/// | one transmitter | one signal on the air |
/// | two transmitters | two signals, on different bands |
/// | anything else | as many as the sponsor allows, one per band |
///
/// Two signals on one band is wrong in every multi-operator class, which is why
/// it is checked whatever the category says. An entry that is neither one nor
/// two transmitters — multi-unlimited, and a single operator with two radios —
/// is only held to that.
public static class TransmitRules
{
    /// What is wrong with this station transmitting now, or null when nothing
    /// is. `others` is every other station of the entry that has its key down.
    public static string? Violation(
        ContestEntry entry,
        Transmitter me,
        IReadOnlyList<Transmitter> others)
    {
        if (others.Count == 0)
        {
            return null;
        }
        if (others.FirstOrDefault(o => SameBand(o, me) && o.Mode == me.Mode) is { } sameMode)
        {
            return $"{sameMode.ComputerName} is transmitting on {Where(me)} as well";
        }
        if (others.FirstOrDefault(o => SameBand(o, me)) is { } sameBand)
        {
            return $"{sameBand.ComputerName} is transmitting on {me.Band?.Name} as well";
        }
        int allowed = Transmitters(entry);
        if (allowed > 0 && others.Count + 1 > allowed)
        {
            string signals = $"{others.Count + 1} signals";
            string on = string.Join(", ", others.Select(Where).Prepend(Where(me)));
            return allowed == 1
                ? $"{signals} on the air — a one-transmitter entry may have one: {on}"
                : $"{signals} on the air — a two-transmitter entry may have two: {on}";
        }
        return null;
    }

    /// How many signals the entry may have at once, or zero when the category
    /// does not say. N1MM reads the number off the operator category on
    /// Cabrillo 2.0 and off the transmitter category after it, and so does
    /// this.
    private static int Transmitters(ContestEntry entry)
    {
        if (!entry.OperatorCategory.StartsWith("MULTI", StringComparison.OrdinalIgnoreCase))
        {
            return 0;
        }
        if (Is(entry, "MULTI-ONE", "ONE"))
        {
            return 1;
        }
        return Is(entry, "MULTI-TWO", "TWO") ? 2 : 0;
    }

    private static bool Is(ContestEntry entry, string operatorCategory, string transmitterCategory) =>
        entry.OperatorCategory.Equals(operatorCategory, StringComparison.OrdinalIgnoreCase)
        || entry.TransmitterCategory.Equals(transmitterCategory, StringComparison.OrdinalIgnoreCase);

    /// Two stations are on the same band only when both say which band they are
    /// on. A station that has not said counts as somewhere else: a guess here
    /// puts a red box in front of an operator who is doing nothing wrong.
    private static bool SameBand(Transmitter one, Transmitter other) =>
        one.Band is not null && other.Band is not null && one.Band == other.Band;

    private static string Where(Transmitter station) =>
        $"{station.Band?.Name ?? "somewhere"} {Named(station.Mode)}".TrimEnd();

    private static string Named(ModeCategory? mode) => mode switch
    {
        ModeCategory.Cw => "CW",
        ModeCategory.Phone => "phone",
        ModeCategory.Digital => "digital",
        _ => "",
    };
}