Added ActionRegistry pattern

docs/Patterns.md

@@ -163,3 +163,118 @@ TODO
 ## ApeDestroy
 
 TODO
+
+## Actions
+
+Action systems allow entities to respond to events. For example, an entity could perform an action when the player presses a key, or could perform an action when the player steps on a button.
+
+Registering a seperate component and system for each action can be tedious. By using an action registry, the component and system can be generated by template code.
+
+```js
+import { System, Component } from 'ape-ecs';
+
+// the action registry
+export class ActionRegistry {
+    constructor(world) {
+        this.world = world;
+    }
+
+    register_action(action_config) {
+        let { action_name, action_setting_properties, on_system_config, on_entity_action } = action_config;
+
+        // Generate a class and register it as a component for the action itself
+        let Action = class extends Component {
+            static get typeName() { return action_name; }//webpack decided not to work with static properties, so I get to do this stupid thing.
+            static get properties() { return { action_key: '' } }//webpack decided not to work with static properties, so I get to do this stupid thing.
+        }
+        this.world.registerComponent(Action);
+
+        // Generate a class and register it as a component for any settings inherent to the action
+        let ActionSettings = class extends Component {
+            static get typeName() { return action_name + 'Settings'; }//webpack decided not to work with static properties, so I get to do this stupid thing.
+            static get properties() { return Object.assign(action_setting_properties, { action_key: '' }); }//webpack decided not to work with static properties, so I get to do this stupid thing.
+        }
+        this.world.registerComponent(ActionSettings);
+
+        // Generate a class and register it as a system for the consequences of an action being performed
+        let ActionSystem = class ActionSystemClass extends System {
+            init() {
+                // set up the actors query
+                this.actors_query = this.createQuery().fromAll(action_name);
+                on_system_config(this);// set up any additional queries
+            }
+            update(currentTick) {
+                // fetch the actors and iterate through them
+                const actors = this.actors_query.refresh().execute();
+                for (let actor of actors) {
+                    let actions = actor.getComponents(action_name);
+
+                    // iterate through the instances of the action
+                    for (let action of actions) {
+                        // find any settings that match this action. Filter for the one with the appropriate key.
+                        let settings = Array.from(actor.getComponents(action_name + 'Settings'));
+                        let specific_setting = settings.find(ele => ele.action_key == action.action_key);
+                        on_entity_action(this, actor, action, specific_setting);
+                    }
+
+                }
+            }
+        }
+        this.world.registerSystem('frame', ActionSystem);
+
+        // Return the classes for later use if you need them.
+        return [ Action, ActionSettings ];
+    }
+}
+
+//create an action registry
+let action_registry = new ActionRegistry(world);
+
+//register the fireProjectile action
+let [FireProjectile, FireProjectileSettings] = action_registry.register_action({
+    action_name: 'FireProjectile',
+    action_setting_properties: {
+        target: EntityRef,
+        image: './assets/stub.png'
+    },
+    on_system_config: (system) => {// set up queries
+        console.log('no queries!');
+    },
+    on_entity_action: (system, entity, action, settings) => {// perform the action
+        if (!settings) {
+            console.log('no settings for FireProjectile.');
+            entity.removeComponent(action);
+            return;
+        }
+
+        console.log('fired')
+
+        // originate the projectile at the entity that acted. 
+        let location = entity.getOne('Location');
+        let target = settings.target.getOne('Location');
+
+        // create the projectile. Assume location, image, and destination components.
+        world.createEntity({
+            components: [
+                {
+                    type: 'Location',
+                    x: location.x,
+                    y: location.y,
+                },
+                {
+                    type: 'Image',
+                    path: settings.image
+                },
+                {
+                    type: 'Destination',
+                    x: target.x,
+                    y: target.y
+                }
+            ]
+        })
+
+        // remove the FireProjectile component
+        entity.removeComponent(action);
+    }
+});
+```