public sealed class Stats : IEquatable<Stats>
{
    public SortedDictionary<Stat, int> Values { get; set; } = new SortedDictionary<Stat, int>();
    public int Count => Values.Sum(pair => Math.Abs(pair.Value));

    public int this[Stat stat]
    {
        get
        {
            return !Values.TryGetValue(stat, out int result) ? 0 : result;
        }
        set
        {
            if (value == 0)
            {
                if (Values.ContainsKey(stat))
                {
                    Values.Remove(stat);
                }

                return;
            }

            Values[stat] = value;
        }
    }

    public Stats() { }

    public Stats(Stats stats)
    {
        foreach (KeyValuePair<Stat, int> pair in stats.Values)
            this[pair.Key] += pair.Value;
    }

    public Stats(BinaryReader reader, int version = int.MaxValue, int customVersion = int.MaxValue)
    {
        int count = reader.ReadInt32();

        for (int i = 0; i < count; i++)
            Values[(Stat)reader.ReadByte()] = reader.ReadInt32();
    }

    public void Add(Stats stats)
    {
        foreach (KeyValuePair<Stat, int> pair in stats.Values)
            this[pair.Key] += pair.Value;
    }

    public void Save(BinaryWriter writer)
    {
        writer.Write(Values.Count);

        foreach (KeyValuePair<Stat, int> pair in Values)
        {
            writer.Write((byte)pair.Key);
            writer.Write(pair.Value);
        }
    }

    public void Clear()
    {
        Values.Clear();
    }

    public bool Equals(Stats other)
    {
        if (Values.Count != other.Values.Count) return false;

        foreach (KeyValuePair<Stat, int> value in Values)
            if (other[value.Key] != value.Value) return false;

        return true;
    }
}

public enum StatFormula : byte
{
    Health,
    Mana,
    Weight,
    Stat
}

public enum Stat : byte
{
    MinAC = 0,
    MaxAC = 1,
    MinMAC = 2,
    MaxMAC = 3,
    MinDC = 4,
    MaxDC = 5,
    MinMC = 6,
    MaxMC = 7,
    MinSC = 8,
    MaxSC = 9,

    Accuracy = 10,
    Agility = 11,
    HP = 12,
    MP = 13,
    AttackSpeed = 14,
    Luck = 15,
    BagWeight = 16,
    HandWeight = 17,
    WearWeight = 18,
    Reflect = 19,
    Strong = 20,
    Holy = 21,
    Freezing = 22,
    PoisonAttack = 23,

    MagicResist = 30,
    PoisonResist = 31,
    HealthRecovery = 32,
    SpellRecovery = 33,
    PoisonRecovery = 34, //TODO - Should this be in seconds or milliseconds??
    CriticalRate = 35,
    CriticalDamage = 36,

    MaxACRatePercent = 40,
    MaxMACRatePercent = 41,
    MaxDCRatePercent = 42,
    MaxMCRatePercent = 43,
    MaxSCRatePercent = 44,
    AttackSpeedRatePercent = 45,
    HPRatePercent = 46,
    MPRatePercent = 47,
    HPDrainRatePercent = 48,

    ExpRatePercent = 100,
    ItemDropRatePercent = 101,
    GoldDropRatePercent = 102,
    MineRatePercent = 103,
    GemRatePercent = 104,
    FishRatePercent = 105,
    CraftRatePercent = 106,
    SkillGainMultiplier = 107,
    AttackBonus = 108,

    LoverExpRatePercent = 120,
    MentorDamageRatePercent = 121,
    MentorExpRatePercent = 123,
    DamageReductionPercent = 124,
    EnergyShieldPercent = 125,
    EnergyShieldHPGain = 126,
    ManaPenaltyPercent = 127,
    TeleportManaPenaltyPercent = 128,
    Hero = 129,

    Unknown = 255
}