namespace Mr.BrickAdventures.Progression;

/// <summary>
/// How far a Skill has been upgraded. Starts at one; there is no zero, because a Playthrough
/// records only the Skills it owns and absence from that record is what "unowned" means.
/// </summary>
public readonly struct SkillLevel : IEquatable<SkillLevel>
{
    public int Value { get; }

    private SkillLevel(int value) => Value = value;

    /// <summary>The level a Skill is at the moment it is first bought.</summary>
    public static readonly SkillLevel First = new(1);

    public SkillLevel Next() => new(Value + 1);

    public bool Equals(SkillLevel other) => Value == other.Value;
    public override bool Equals(object? obj) => obj is SkillLevel other && Equals(other);
    public override int GetHashCode() => Value;
    public override string ToString() => Value.ToString();

    public static SkillLevel Of(int value) => value < 1
        ? throw new ArgumentOutOfRangeException(nameof(value), value, "A skill level starts at 1; unowned is absence, not level 0.")
        : new SkillLevel(value);
}