namespace HSchool.Simulation;

/// <summary>Which word list the random-name button draws from.</summary>
public enum SchoolNameLanguage
{
    Russian = 0,
    English = 1,
}

/// <summary>
/// Suggestions for the "random name" button. Lives here rather than in the client because the
/// server is the one that knows which names are already taken.
/// </summary>
public sealed class SchoolNameGenerator(Random? random = null)
{
    private const int AttemptsBeforeNumbering = 24;

    private readonly record struct Catalog(
        string[] Kinds,
        string[] Epithets,
        string NumberSign,
        bool NumberSpace,
        bool EpithetFirst,
        string FallbackKind);

    private static readonly Catalog Russian = new(
        ["Школа", "Гимназия", "Лицей", "Школа-интернат"],
        [
            "Северная", "Приморская", "Заречная", "Нагорная", "Слободская", "Озёрная",
            "Кленовая", "Рябиновая", "Солнечная", "Луговая", "Тихая", "Ясная",
        ],
        "№",
        false,
        false,
        "Школа");

    private static readonly Catalog English = new(
        ["School", "Academy", "Grammar School", "High School"],
        [
            "Northern", "Seaside", "Riverside", "Hillside", "Maple", "Rowan",
            "Sunny", "Meadow", "Quiet", "Clear", "Oak", "Pine",
        ],
        "No.",
        true,
        true,
        "School");

    private readonly Random _random = random ?? Random.Shared;

    /// <summary>
    /// A name that is not in <paramref name="taken"/>. Falls back to a numbered name so the
    /// button always produces something, even when the pool is exhausted.
    /// </summary>
    public string Next(IEnumerable<string> taken, SchoolNameLanguage language = SchoolNameLanguage.Russian)
    {
        var catalog = language == SchoolNameLanguage.English ? English : Russian;
        var used = new HashSet<string>(taken, StringComparer.OrdinalIgnoreCase);

        for (var attempt = 0; attempt < AttemptsBeforeNumbering; attempt++)
        {
            var candidate = Compose(catalog);
            if (used.Add(candidate))
            {
                return candidate;
            }
        }

        for (var number = 1; ; number++)
        {
            var candidate = Numbered(catalog, catalog.FallbackKind, number);
            if (!used.Contains(candidate))
            {
                return candidate;
            }
        }
    }

    private string Compose(Catalog catalog)
    {
        var kind = catalog.Kinds[_random.Next(catalog.Kinds.Length)];

        // Half the names are numbered, half are named — both read like a real school.
        if (_random.Next(2) == 0)
        {
            return Numbered(catalog, kind, _random.Next(1, 100));
        }

        var epithet = catalog.Epithets[_random.Next(catalog.Epithets.Length)];
        return catalog.EpithetFirst
            ? $"{epithet} {kind}"
            : $"{kind} «{epithet}»";
    }

    private static string Numbered(Catalog catalog, string kind, int number) =>
        catalog.NumberSpace
            ? $"{kind} {catalog.NumberSign} {number}"
            : $"{kind} {catalog.NumberSign}{number}";
}