public void RemoveTierFromUpgradeOptions(Tier tier, Tier toRemove) => GetUpgradeOptions(tier).AddTier(toRemove);
public IEnumerable <Tier> GetNext(Tier tier) => GetUpgradeOptions(tier)?.NextTiers ?? Array.Empty <Tier>();
public void AddTierToUpgradeOptions(Tier tier, Tier toAdd) => GetUpgradeOptions(tier).AddTier(toAdd);
public UpgradeOptions GetUpgradeOptions(Tier tier) => _upgradeOptions.FirstOrDefault(x => x.Tier.Equals(tier));