PKHeX/PKHeX.Core/Legality/Structures/IVersion.cs

namespace PKHeX.Core;

/// <summary>
/// Interface that exposes a <see cref="Version"/> to see which version the data originated in.
/// </summary>
public interface IVersion
{
    /// <summary>
    /// The version the data originated in.
    /// </summary>
    GameVersion Version { get; }
}

public static partial class Extensions
{
    private static bool CanBeReceivedBy(this IVersion ver, GameVersion game) => ver.Version.Contains(game);

    public static GameVersion GetCompatibleVersion(this IVersion ver, GameVersion prefer)
    {
        if (ver.CanBeReceivedBy(prefer) || ver.Version <= GameVersion.Unknown)
            return prefer;
        return ver.GetSingleVersion();
    }

    private static GameVersion GetSingleVersion(this IVersion ver)
    {
        const int max = (int)GameUtil.HighestGameID;
        if ((int)ver.Version <= max)
            return ver.Version;
        var rnd = Util.Rand;
        while (true) // this isn't optimal, but is low maintenance
        {
            var game = (GameVersion)rnd.Next(1, max);
            if (game == GameVersion.BU)
                continue; // Ignore this one; only can be Japanese language.
            if (ver.CanBeReceivedBy(game))
                return game;
        }
    }
}