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resources/app/client-esm/data/region-behaviors/base.mjs

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+import TypeDataModel from "../../../common/abstract/type-data.mjs";
+import * as fields from "../../../common/data/fields.mjs";
+
+/**
+ * The data model for a behavior that receives Region events.
+ * @extends TypeDataModel
+ * @memberof data.behaviors
+ * @abstract
+ *
+ * @property {Set<string>} events    The Region events that are handled by the behavior.
+ */
+export default class RegionBehaviorType extends TypeDataModel {
+
+  /**
+   * Create the events field.
+   * @param {object} options      Options which configure how the events field is declared
+   * @param {string[]} [options.events]     The event names to restrict to.
+   * @param {string[]} [options.initial]    The initial set of events that should be default for the field
+   * @returns {fields.SetField}
+   * @protected
+   */
+  static _createEventsField({events, initial}={}) {
+    const setFieldOptions = {
+      label: "BEHAVIOR.TYPES.base.FIELDS.events.label",
+      hint: "BEHAVIOR.TYPES.base.FIELDS.events.hint"
+    };
+    if ( initial ) setFieldOptions.initial = initial;
+    return new fields.SetField(new fields.StringField({
+      required: true,
+      choices: Object.values(CONST.REGION_EVENTS).reduce((obj, e) => {
+        if ( events && !events.includes(e) ) return obj;
+        obj[e] = `REGION.EVENTS.${e}.label`;
+        return obj;
+      }, {})
+    }), setFieldOptions);
+  }
+
+  /* ---------------------------------------- */
+
+  /**
+   * @callback EventBehaviorStaticHandler  Run in the context of a {@link RegionBehaviorType}.
+   * @param {RegionEvent} event
+   * @returns {Promise<void>}
+   */
+
+  /**
+   * A RegionBehaviorType may register to always receive certain events by providing a record of handler functions.
+   * These handlers are called with the behavior instance as its bound scope.
+   * @type {Record<string, EventBehaviorStaticHandler>}
+   */
+  static events = {};
+
+  /* ---------------------------------------- */
+
+  /**
+   * The events that are handled by the behavior.
+   * @type {Set<string>}
+   */
+  events = this.events ?? new Set();
+
+  /* ---------------------------------------- */
+
+  /**
+   * A convenience reference to the RegionBehavior which contains this behavior sub-type.
+   * @type {RegionBehavior|null}
+   */
+  get behavior() {
+    return this.parent;
+  }
+
+  /* ---------------------------------------- */
+
+  /**
+   * A convenience reference to the RegionDocument which contains this behavior sub-type.
+   * @type {RegionDocument|null}
+   */
+  get region() {
+    return this.behavior?.region ?? null;
+  }
+
+  /* ---------------------------------------- */
+
+  /**
+   * A convenience reference to the Scene which contains this behavior sub-type.
+   * @type {Scene|null}
+   */
+  get scene() {
+    return this.behavior?.scene ?? null;
+  }
+
+  /* ---------------------------------------- */
+
+  /**
+   * Handle the Region event.
+   * @param {RegionEvent} event    The Region event
+   * @returns {Promise<void>}
+   * @protected
+   * @internal
+   */
+  async _handleRegionEvent(event) {}
+}