/// <summary>
        /// Attack another character. Hits if our role is greater than the
        /// opponent's armor class.
        /// </summary>
        /// <param name='opponent'>Whom we are attacking.</param>
        /// <param name='roll'>An int from 1-20.</param>
        public AttackResult Attack(Character opponent, int roll)
        {
            if(opponent == null) {
                throw new ArgumentException("opponent cannot be null");
            }
            Helpers.ValidateD20Value("roll", roll);

            var attackerStrengthModifier = this.modifierTable[this.Attacker.Strength - 1];
            var modifiedRoll = roll + attackerStrengthModifier;
            var modifiedArmorClass = opponent.ArmorClass + this.modifierTable[opponent.Dexterity - 1];

            var result = AttackResult.Miss;
            var damage = 0;

            if(roll == 20) {
                result = AttackResult.CriticalHit;
                damage = 2 + (2 * attackerStrengthModifier);
            }
            else if(modifiedRoll >= modifiedArmorClass) {
                result = AttackResult.Hit;
                damage = 1 + attackerStrengthModifier;
            }

            if((result == AttackResult.Hit || result == AttackResult.CriticalHit) && damage < 1) {
                damage = 1;
            }

            opponent.HitPoints -= damage;

            return result;
        }
 /// <summary>
 /// Initializes a new instance of the <see cref="EverCraft.CombatCalculator"/> class.
 /// </summary>
 /// <param name='attacker'>
 /// The attacking character.
 /// </param>
 public CombatCalculator(Character attacker)
 {
     this.Attacker = attacker;
 }