I'm working on the server side of a turn-based strategy game. The game has a really complex combat system, like:

When you are hit, you summon a phoenix to attack the enemy that deals X damage, and the phoenix fly back to heal Y of your health.

Well, such skill does sounds interesting, but requires a great amount of work on the skill and combat system.

We did not use script on the server. We just split one skill into several skill effects. For instance, we have DamageEffect, AddBuffEffect and so on. However, we have a lot of skills like the phoenix stuff above, they can be triggered at a specific moment. And some of them even replace the main attack skill. So we designed several SkillConditions for that. It worked, although not very well.

However, the question is: For such a complex combat system, how to define the protocol between client and server?

For example:

A attacks B using skill X for 30 damage points. B uses the phoenix skill Y when he is hit that damage A for 20 points, and heals himself 10 points.

How can we express this to the client? We currently use a structure like this:

useSkillAction:
    skill: id_of_X
    source: id_of_A
    target: id_of_B
    subActions:
        damageAction:
            timing: onHit  // Timing means the the damageAction will trigger when the skill animation triggers a 'hit' event.
            character: id_of_B
            damage: 30
            subActions:
                propertyChangedAction:
                    timing: onFinished
                    character: id_of_B
                    property: health
                    value: health_of_B
                useSkillAction:
                    timing: onFinished
                    skill: id_of_Y
                    source: id_of_B
                    target: id_of_A
                    subActions:
                        damageAction:
                            timing: onHit
                            character: id_of_A
                            damage: 20
                            subActions:
                                propertyChangedAction:
                                    timing: onFinished
                                    character: id_of_A
                                    property: health
                                    value: health_of_A
                        healAction:
                            timing: onFlyBack??
                            character: id_of_B
                            damage: 10
                            subActions:
                                propertyChangedAction:
                                    timing: onFinished
                                    character: id_of_B
                                    property: health
                                    value: health_of_B

Well, I think you got the idea. For now, this structure can handle only simple skills. The solution currently have three problems:

1. For complex skills, like above, it's hard to describe the timing of phoenix fly back.
2. For the onHit timing in damageAction, that means the server even knows that there's an animation trigger called 'hit'.
3. It's hard to maintain.

Is there a better way to do this? Thanks anyway, for my broken English...