# Combat base framework
Combat is core to many games. Exactly how it works is very game-dependent. In this lesson we will build a framework to implement two common flavors:
- "Twitch-based" combat ([specific lesson here](./Beginner-Tutorial-Combat-Twitch.md)) means that you perform a combat action by entering a command, and after some delay (which may depend on your skills etc), the action happens. It's called 'twitch' because actions often happen fast enough that changing your strategy may involve some element of quick thinking and a 'twitchy trigger finger'.
- "Turn-based" combat ([specific lesson here](./Beginner-Tutorial-Combat-Turnbased.md)) means that players input actions in clear turns. Timeout for entering/queuing your actions is often much longer than twitch-based style. Once everyone made their choice (or the timeout is reached), everyone's action happens all at once, after which the next turn starts. This style of combat requires less player reflexes.
We will design a base combat system that supports both styles.
- We need a `CombatHandler` to track the progress of combat. This will be a [Script](../../../Components/Scripts.md). Exactly how this works (and where it is stored) will be a bit different between Twitch- and Turnbased combat. We will create its common framework in this lesson.
- Combat are divided into _actions_. We want to be able to easily extend our combat with more possible actions. An action needs Python code to show what actually happens when the action is performed. We will define such code in `Action` classes.
- We also need a way to describe a _specific instance_ of a given action. That is, when we do an "attack" action, we need at the minimum to know who is being attacked. For this will we use Python `dicts` that we will refer to as `action_dicts`.
## CombatHandler
> Create a new module `evadventure/combat_base.py`
```{sidebar}
Under `evennia/contrib/tutorials/evadventure/`, in [combat_base.py](evennia.contrib.tutorials.evadventure.combat_base) you'll find a complete implementation of the base combat module.
```
Our "Combat Handler" will handle the administration around combat. It needs to be _persistent_ (even is we reload the server your combat should keep going).
Creating the CombatHandler is a little of a catch-22 - how it works depends on how Actions and Action-dicts look. But without having the CombatHandler, it's hard to know how to design Actions and Action-dicts. So we'll start with its general structure and fill out the details later in this lesson.
Below, methods with `pass` will be filled out this lesson while those raising `NotImplementedError` will be different for Twitch/Turnbased combat and will be implemented in their respective lessons following this one.
```python
# in evadventure/combat_base.py
from evennia import DefaultScript
class CombatFailure(RuntimeError):
"""If some error happens in combat"""
pass
class EvAdventureCombatBaseHandler(DefaultSCript):
"""
This should be created when combat starts. It 'ticks' the combat
and tracks all sides of it.
"""
# common for all types of combat
action_classes = {} # to fill in later
fallback_action_dict = {}
@classmethod
def get_or_create_combathandler(cls, obj, **kwargs):
""" Get or create combathandler on `obj`."""
pass
def msg(self, message, combatant=None, broadcast=True, location=True):
"""
Send a message to all combatants.
"""
pass # TODO
def get_combat_summary(self, combatant):
"""
Get a nicely formatted 'battle report' of combat, from the
perspective of the combatant.
"""
pass # TODO
# implemented differently by Twitch- and Turnbased combat
def get_sides(self, combatant):
"""
Get who's still alive on the two sides of combat, as a
tuple `([allies], [enemies])` from the perspective of `combatant`
(who is _not_ included in the `allies` list.
"""
raise NotImplementedError
def give_advantage(self, recipient, target):
"""
Give advantage to recipient against target.
"""
raise NotImplementedError
def give_disadvantage(self, recipient, target):
"""
Give disadvantage to recipient against target.
"""
raise NotImplementedError
def has_advantage(self, combatant, target):
"""
Does combatant have advantage against target?
"""
raise NotImplementedError
def has_disadvantage(self, combatant, target):
"""
Does combatant have disadvantage against target?
"""
raise NotImplementedError
def queue_action(self, combatant, action_dict):
"""
Queue an action for the combatant by providing
action dict.
"""
raise NotImplementedError
def execute_next_action(self, combatant):
"""
Perform a combatant's next action.
"""
raise NotImplementedError
def start_combat(self):
"""
Start combat.
"""
raise NotImplementedError
def check_stop_combat(self):
"""
Check if the combat is over and if it should be stopped.
"""
raise NotImplementedError
def stop_combat(self):
"""
Stop combat and do cleanup.
"""
raise NotImplementedError
```
The Combat Handler is a [Script](../../../Components/Scripts.md). Scripts are typeclassed entities, which means that they are persistently stored in the database. Scripts can optionally be stored "on" other objects (such as on Characters or Rooms) or be 'global' without any such connection. While Scripts has an optional timer component, it is not active by default and Scripts are commonly used just as plain storage. Since Scripts don't have an in-game existence, they are great for storing data on 'systems' of all kinds, including our combat.
Let's implement the generic methods we need.
### CombatHandler.get_or_create_combathandler
A helper method for quickly getting the combathandler for an ongoing combat and combatant.
We expect to create the script "on" an object (which one we don't know yet, but we expect it to be a typeclassed entity).
```python
# in evadventure/combat_base.py
from evennia import create_script
# ...
class EvAdventureCombatBaseHandler(DefaultScript):
# ...
@classmethod
def get_or_create_combathandler(cls, obj, **kwargs):
"""
Get or create a combathandler on `obj`.
Args:
obj (any): The Typeclassed entity to store this Script on.
Keyword Args:
combathandler_key (str): Identifier for script. 'combathandler' by
default.
**kwargs: Extra arguments to the Script, if it is created.
"""
if not obj:
raise CombatFailure("Cannot start combat without a place to do it!")
combathandler_key = kwargs.pop("key", "combathandler")
combathandler = obj.ndb.combathandler
if not combathandler or not combathandler.id:
combathandler = obj.scripts.get(combathandler_key).first()
if not combathandler:
# have to create from scratch
persistent = kwargs.pop("persistent", True)
combathandler = create_script(
cls,
key=combathandler_key,
obj=obj,
persistent=persistent,
**kwargs,
)
obj.ndb.combathandler = combathandler
return combathandler
# ...
```
This helper method uses `obj.scripts.get()` to find if the combat script already exists 'on' the provided `obj`. If not, it will create it using Evennia's [create_script](evennia.utils.create.create_script) function. For some extra speed we cache the handler as `obj.ndb.combathandler` The `.ndb.` (non-db) means that handler is cached only in memory.
```{sidebar} Checking .id (or .pk)
When getting it from cache, we make sure to also check if the combathandler we got has a database `.id` that is not `None` (we could also check `.pk`, stands for "primary key") . If it's `None`, this means the database entity was deleted and we just got its cached python representation from memory - we need to recreate it.
```
`get_or_create_combathandler` is decorated to be a [classmethod](https://docs.python.org/3/library/functions.html#classmethod), meaning it should be used on the handler class directly (rather than on an _instance_ of said class). This makes sense because this method actually should return the new instance.
As a class method we'll need to call this directly on the class, like this:
```python
combathandler = EvAdventureCombatBaseHandler.get_or_create_combathandler(combatant)
```
The result will be a new handler _or_ one that was already defined.
### CombatHandler.msg
```python
# in evadventure/combat_base.py
# ...
class EvAdventureCombatBaseHandler(DefaultScript):
# ...
def msg(self, message, combatant=None, broadcast=True, location=None):
"""
Central place for sending messages to combatants. This allows
for adding any combat-specific text-decoration in one place.
Args:
message (str): The message to send.
combatant (Object): The 'You' in the message, if any.
broadcast (bool): If `False`, `combatant` must be included and
will be the only one to see the message. If `True`, send to
everyone in the location.
location (Object, optional): If given, use this as the location to
send broadcast messages to. If not, use `self.obj` as that
location.
Notes:
If `combatant` is given, use `$You/you()` markup to create
a message that looks different depending on who sees it. Use
`$You(combatant_key)` to refer to other combatants.
"""
if not location:
location = self.obj
location_objs = location.contents
exclude = []
if not broadcast and combatant:
exclude = [obj for obj in location_objs if obj is not combatant]
location.msg_contents(
message,
exclude=exclude,
from_obj=combatant,
mapping={locobj.key: locobj for locobj in location_objs},
)
# ...
```
```{sidebar}
The `self.obj` property of a Script is the entity on which the Script 'sits'. If set on a Character, `self.obj` will be that Character. If on a room, it'd be that room. For a global script, `self.obj` is `None`.
```
We saw the `location.msg_contents()` method before in the [Weapon class of the Objects lesson](./Beginner-Tutorial-Objects.md#weapons). Its purpose is to take a string on the form `"$You() do stuff against $you(key)"` and make sure all sides see a string suitable just to them. Our `msg()` method will by default broadcast the message to everyone in the room.
You'd use it like this:
```python
combathandler.msg(
f"$You() $conj(throw) {item.key} at $you({target.key}).",
combatant=combatant,
location=combatant.location
)
```
If combatant is `Trickster`, `item.key` is "a colorful ball" and `target.key` is "Goblin", then
The combatant would see:
You throw a colorful ball at Goblin.
The Goblin sees
Trickster throws a colorful ball at you.
Everyone else in the room sees
Trickster throws a colorful ball at Goblin.
### Combathandler.get_combat_summary
We want to be able to show a nice summary of the current combat:
```shell
Goblin shaman (Perfect)
Gregor (Hurt) Goblin brawler(Hurt)
Bob (Perfect) vs Goblin grunt 1 (Hurt)
Goblin grunt 2 (Perfect)
Goblin grunt 3 (Wounded)
```
```{code-block} python
:linenos:
:emphasize-lines: 15,17,21,22,28,41
# in evadventure/combat_base.py
# ...
from evennia import EvTable
# ...
class EvAdventureCombatBaseHandler(DefaultScript):
# ...
def get_combat_summary(self, combatant):
allies, enemies = self.get_sides(combatant)
nallies, nenemies = len(allies), len(enemies)
# prepare colors and hurt-levels
allies = [f"{ally} ({ally.hurt_level})" for ally in allies]
enemies = [f"{enemy} ({enemy.hurt_level})" for enemy in enemies]
# the center column with the 'vs'
vs_column = ["" for _ in range(max(nallies, nenemies))]
vs_column[len(vs_column) // 2] = "|wvs|n"
# the two allies / enemies columns should be centered vertically
diff = abs(nallies - nenemies)
top_empty = diff // 2
bot_empty = diff - top_empty
topfill = ["" for _ in range(top_empty)]
botfill = ["" for _ in range(bot_empty)]
if nallies >= nenemies:
enemies = topfill + enemies + botfill
else:
allies = topfill + allies + botfill
# make a table with three columns
return evtable.EvTable(
table=[
evtable.EvColumn(*allies, align="l"),
evtable.EvColumn(*vs_column, align="c"),
evtable.EvColumn(*enemies, align="r"),
],
border=None,
maxwidth=78,
)
# ...
```
This may look complex, but the complexity is only in figuring out how to organize three columns, especially how to to adjust to the two sides on each side of the `vs` are roughly vertically aligned.
- **Line 15** : We make use of the `self.get_sides(combatant)` method which we haven't actually implemented yet. This is because turn-based and twitch-based combat will need different ways to find out what the sides are. The `allies` and `enemies` are lists.
- **Line 17**: The `combatant` is not a part of the `allies` list (this is how we defined `get_sides` to work), so we insert it at the top of the list (so they show first on the left-hand side).
- **Lines 21, 22**: We make use of the `.hurt_level` values of all living things (see the [LivingMixin of the Character lesson](./Beginner-Tutorial-Characters.md)).
- **Lines 28-39**: We determine how to vertically center the two sides by adding empty lines above and below the content.
- **Line 41**: The [Evtable](../../../Components/EvTable.md) is an Evennia utility for making, well, text tables. Once we are happy with the columns, we feed them to the table and let Evennia do the rest. It's worth to explore `EvTable` since it can help you create all sorts of nice layouts.
## Actions
In EvAdventure we will only support a few common combat actions, mapping to the equivalent rolls and checks used in _Knave_. We will design our combat framework so that it's easy to expand with other actions later.
- `hold` - The simplest action. You just lean back and do nothing.
- `attack` - You attack a given `target` using your currently equipped weapon. This will become a roll of STR or WIS against the targets' ARMOR.
- `stunt` - You make a 'stunt', which in roleplaying terms would mean you tripping your opponent, taunting or otherwise trying to gain the upper hand without hurting them. You can do this to give yourself (or an ally) _advantage_ against a `target` on the next action. You can also give a `target` _disadvantage_ against you or an ally for their next action.
- `use item` - You make use of a `Consumable` in your inventory. When used on yourself, it'd normally be something like a healing potion. If used on an enemy it could be a firebomb or a bottle of acid.
- `wield` - You wield an item. Depending on what is being wielded, it will be wielded in different ways: A helmet will be placed on the head, a piece of armor on the chest. A sword will be wielded in one hand, a shield in another. A two-handed axe will use up two hands. Doing so will move whatever was there previously to the backpack.
- `flee` - You run away/disengage. This action is only applicable in turn-based combat (in twitch-based combat you just move to another room to flee). We will thus wait to define this action until the [Turnbased combat lesson](./Beginner-Tutorial-Combat-Turnbased.md).
## Action dicts
To pass around the details of an attack (the second point above), we will use a `dict`. A `dict` is simple and also easy to save in an `Attribute`. We'll call this the `action_dict` and here's what we need for each action.
> You don't need to type these out anywhere, it's listed here for reference. We will use these dicts when calling `combathandler.queue_action(combatant, action_dict)`.
```python
hold_action_dict = {
"key": "hold"
}
attack_action_dict = {
"key": "attack",
"target":
}
stunt_action_dict = {
"key": "stunt",
"recipient": , # who gains advantage/disadvantage
"target": , # who the recipient gainst adv/dis against
"advantage": bool, # grant advantage or disadvantage?
"stunt_type": Ability, # Ability to use for the challenge
"defense_type": Ability, # what Ability for recipient to defend with if we
# are trying to give disadvantage
}
use_item_action_dict = {
"key": "use",
"item":