namespace HSchool.People;

/// <summary>
/// A name set can speak several native languages; the school picks one. Empty request rolls from
/// the school seed so the same create always lands on the same tongue.
/// </summary>
public static class NativeLanguages
{
    public static bool Allows(NameSetDef names, string skill) =>
        names.Spoken.Contains(skill, StringComparer.Ordinal);

    /// <summary>
    /// <paramref name="requested"/> must already be in the set, or empty. Invalid ids return
    /// null so the create path can 400. When omitted, a new school rolls; a reload without a
    /// saved pick takes the first listed language so old saves do not reshuffle intake.
    /// </summary>
    public static string? Pick(NameSetDef names, int schoolSeed, string? requested, bool rollIfOmitted)
    {
        var spoken = names.Spoken;
        if (spoken.Count == 0)
        {
            return null;
        }

        if (!string.IsNullOrWhiteSpace(requested))
        {
            return Allows(names, requested) ? requested : null;
        }

        if (!rollIfOmitted || spoken.Count == 1)
        {
            return spoken[0];
        }

        var rng = new Random(Seed.ForSchool(schoolSeed, Seed.NativeLanguageSalt));
        return spoken[rng.Next(spoken.Count)];
    }
}