Skill Class design : How to deal with multiple criteria

Question

I'm planning to make a Class for RPG game's character skill. But the problem is that the skills need to be classified by multiple criteria. Below are the criteria for skills.

1. Independent / dependent

Some skills are usuable by itself. Howver some skills are only used (automatically) in situations where certain skills are used. For example 'Additinal FireBall' skill are only used after 'FireBall' skill.

2. Attack / Buff

Attack skills deal damage to enemy. On the contrary buff skills do some useful effects like increasing character's movement speed.

abstract class Skill {
    String skillId;

    abstract void use(Character character, Enemy enemy);
}

abstract class IndepentdentSkill {
}

abstract class DependentSkill {
    List<String> conditionSkills; //DependentSkill are automatically used after one of conditionSkills are used
}

interface AttackSkill {
    void doDamage(Enemy enemy);
}

interface BuffSkill {
    void applyBuff(Character character);
}

class IndependentAttackSkill extends IndepentdentSkill implements AttackSkill {
    @Override
    void use(Character character, Enemy enemy) {
        doDamage(enemey);
    }

    @Override
    void doDamage(Enemy enemy) {
        enemy.takeDamage(this.damage);
    }
}

class IndependentBuffSkill extends IndepentdentSkill implements BuffSkill {
    List<BuffEffects> BuffEffects;

    @Override
    void use(Character character, Enemy enemy) {
        doDamage(enemey);
    }

    @Override
    void applyBuff(Character character) {
        character.applyBuff(this.BuffEffects);
    }
}

//class DependentAttackSkill { ... }
//class DependentBuffSkill { ... }

I tried to make class like below but there were several problems.

1. In this example, there will be four(2 * 2) class in total(IndependentAttackSkill, ..., DependentBuffSkill). If I need one more criteria and it would be 2 * 2 * 2 = 8. Moreover, if I have to add 'Defense' classification there would be a lot of work.

2. method Skill.use(Character, Enemy) are taking parameter more than necessary. As you can see in the concrete Class, Skill.use() only use one of them.

If you know a class design that can complement these two issues, I would really appreciate it if you could let me know

Answer 1

When I made a Tactical RPG a couple years ago, I had a class for Actionss that can be used in combat as a one-time action and StatusEffects that remain on a Combatant* and do... something.

A Skill can enable a combatant to use an Action (which the player would consider an "active skill") and/or bestow a permanent StatusEffect on them (which the player would consider a "passive skill"). Using an Action usually does damage, but can also result in bestowing temporary StatusEffects on one or more combatants (which the player would call a "buff"/"debuff") or do something entirely different.

The Action class is pretty straight-forward: It has various properties that say on what kind of targets it can be used (allies, enemies, tiles or perhaps no specific target at all), in what range, with what area of effect and at what cost it can be used. And then it gets a use(Combatant user, List<Combatant> targets) method that can be overridden by derived classes to contain custom code that actually does stuff. Like inflict damage or bestow status effects.

The StatusEffect class is basically an event handler. A class inheriting from StatusEffect can subscribe to various events while active. When such an event happens (combatant stats are recalculated, combatant turn begins, combatant uses an Action, combatant receives damage...), the game checks if any active status effects subscribed to these events and then calls their handler method, which then get an opportunity to influence the results.

_{* I usually don't like having separate classes for Character and Enemy. I usually have one class Combatant that represents any participants in a combat and has a property that says which team it is fighting for.}