namespace Mr.BrickAdventures.Progression;

/// <summary>
/// The authored ordering of Levels that defines progression. Shared by every Playthrough — it is
/// authored data, not per-Playthrough state, and carries no scene or presentation detail.
/// </summary>
public sealed class Campaign
{
    private readonly List<LevelId> _levels;

    private Campaign(List<LevelId> levels) => _levels = levels;

    public static Campaign Of(IEnumerable<LevelId> levels)
    {
        var ordered = levels.ToList();

        if (ordered.Count == 0)
            throw new ArgumentException("A campaign needs at least one level.", nameof(levels));

        if (ordered.Distinct().Count() != ordered.Count)
            throw new ArgumentException("A campaign cannot list the same level twice.", nameof(levels));

        return new Campaign(ordered);
    }

    public LevelId First => _levels[0];

    /// <summary>
    /// The Level after <paramref name="level"/>, or null if it is the last one or not in this
    /// Campaign at all.
    /// </summary>
    public LevelId? Next(LevelId level)
    {
        var at = _levels.IndexOf(level);
        return at >= 0 && at + 1 < _levels.Count ? _levels[at + 1] : null;
    }
}