using Nonemm.Contests;

namespace Nonemm.Session;

/// What the operator has typed: the callsign, a value per exchange box, and
/// which box the cursor is in. The callsign box is field 0.
public sealed class EntryFields
{
    private readonly List<string> values;

    public EntryFields(IReadOnlyList<ExchangeField> exchange)
    {
        Exchange = exchange;
        values = [.. Enumerable.Repeat("", exchange.Count)];
    }

    public IReadOnlyList<ExchangeField> Exchange { get; }

    /// Raised when the callsign box goes from empty to holding something. That
    /// is where N1MM takes the serial number for the contact, so the number is
    /// out on the network before the contact is worked.
    public event EventHandler? CallStarted;

    public string Call
    {
        get;
        set
        {
            bool wasEmpty = field.Trim().Length == 0;
            field = value;
            if (wasEmpty && field.Trim().Length > 0)
            {
                CallStarted?.Invoke(this, EventArgs.Empty);
            }
        }
    } = "";

    /// 0 is the callsign box; 1 and up are the exchange boxes in order.
    public int Focus { get; private set; }

    public int FieldCount => Exchange.Count + 1;

    public string this[int field]
    {
        get => field == 0 ? Call : values[field - 1];
        set
        {
            if (field == 0)
            {
                Call = value;
            }
            else
            {
                values[field - 1] = value;
            }
        }
    }

    public string ValueOf(ExchangeSlot slot)
    {
        for (int at = 0; at < Exchange.Count; at++)
        {
            if (Exchange[at].Slot == slot)
            {
                return values[at];
            }
        }
        return "";
    }

    public void Set(ExchangeSlot slot, string value)
    {
        for (int at = 0; at < Exchange.Count; at++)
        {
            if (Exchange[at].Slot == slot)
            {
                values[at] = value;
            }
        }
    }

    public void FocusOn(int field) => Focus = Math.Clamp(field, 0, FieldCount - 1);

    /// What space and tab do: move to the next box the operator types in, and
    /// round to the callsign again from the last one. The report boxes and the
    /// sent serial are stepped over, because nobody types 599 or the number
    /// they are sending — N1MM steps over the same three and fills them in.
    public void Advance() => Focus = Next(1);

    public void Retreat() => Focus = Next(-1);

    private int Next(int by)
    {
        int at = Focus;
        for (int step = 0; step < FieldCount; step++)
        {
            at = (at + by + FieldCount) % FieldCount;
            if (at == 0 || !IsFilledIn(Exchange[at - 1]))
            {
                return at;
            }
        }
        return Focus;
    }

    private static bool IsFilledIn(ExchangeField field) =>
        field.IsSent || field.Kind == ExchangeFieldKind.Report;

    /// True when the operator has typed nothing. The boxes holding what this
    /// station sends are filled in by the program, so they do not count.
    public bool IsEmpty =>
        Call.Trim().Length == 0 &&
        Exchange.Where((f, at) => !f.IsSent && values[at].Trim().Length > 0).Any() == false;

    /// True when everything the contest asks for has been typed.
    public bool IsComplete =>
        Call.Trim().Length > 0 &&
        Exchange.Where((f, at) => f.IsRequired && values[at].Trim().Length == 0).Any() == false;

    public void Clear()
    {
        Call = "";
        for (int at = 0; at < values.Count; at++)
        {
            values[at] = "";
        }
        Focus = 0;
    }
}