ecsy/src/System.js

Entity Component System in JS

import Query from "./Query.js";
import { componentRegistered } from "./Utils.js";

export class System {
  canExecute() {
    if (this._mandatoryQueries.length === 0) return true;

    for (let i = 0; i < this._mandatoryQueries.length; i++) {
      var query = this._mandatoryQueries[i];
      if (query.entities.length === 0) {
        return false;
      }
    }

    return true;
  }

  getName() {
    return this.constructor.getName();
  }

  constructor(world, attributes) {
    this.world = world;
    this.enabled = true;

    // @todo Better naming :)
    this._queries = {};
    this.queries = {};

    this.priority = 0;

    // Used for stats
    this.executeTime = 0;

    if (attributes && attributes.priority) {
      this.priority = attributes.priority;
    }

    this._mandatoryQueries = [];

    this.initialized = true;

    if (this.constructor.queries) {
      for (var queryName in this.constructor.queries) {
        var queryConfig = this.constructor.queries[queryName];
        var Components = queryConfig.components;
        if (!Components || Components.length === 0) {
          throw new Error("'components' attribute can't be empty in a query");
        }

        // Detect if the components have already been registered
        let unregisteredComponents = Components.filter(
          (Component) => !componentRegistered(Component)
        );

        if (unregisteredComponents.length > 0) {
          throw new Error(
            `Tried to create a query '${
              this.constructor.name
            }.${queryName}' with unregistered components: [${unregisteredComponents
              .map((c) => c.getName())
              .join(", ")}]`
          );
        }

        var query = this.world.entityManager.queryComponents(Components);

        this._queries[queryName] = query;
        if (queryConfig.mandatory === true) {
          this._mandatoryQueries.push(query);
        }
        this.queries[queryName] = {
          results: query.entities,
        };

        // Reactive configuration added/removed/changed
        var validEvents = ["added", "removed", "changed"];

        const eventMapping = {
          added: Query.prototype.ENTITY_ADDED,
          removed: Query.prototype.ENTITY_REMOVED,
          changed: Query.prototype.COMPONENT_CHANGED, // Query.prototype.ENTITY_CHANGED
        };

        if (queryConfig.listen) {
          validEvents.forEach((eventName) => {
            if (!this.execute) {
              console.warn(
                `System '${this.getName()}' has defined listen events (${validEvents.join(
                  ", "
                )}) for query '${queryName}' but it does not implement the 'execute' method.`
              );
            }

            // Is the event enabled on this system's query?
            if (queryConfig.listen[eventName]) {
              let event = queryConfig.listen[eventName];

              if (eventName === "changed") {
                query.reactive = true;
                if (event === true) {
                  // Any change on the entity from the components in the query
                  let eventList = (this.queries[queryName][eventName] = []);
                  query.eventDispatcher.addEventListener(
                    Query.prototype.COMPONENT_CHANGED,
                    (entity) => {
                      // Avoid duplicates
                      if (eventList.indexOf(entity) === -1) {
                        eventList.push(entity);
                      }
                    }
                  );
                } else if (Array.isArray(event)) {
                  let eventList = (this.queries[queryName][eventName] = []);
                  query.eventDispatcher.addEventListener(
                    Query.prototype.COMPONENT_CHANGED,
                    (entity, changedComponent) => {
                      // Avoid duplicates
                      if (
                        event.indexOf(changedComponent.constructor) !== -1 &&
                        eventList.indexOf(entity) === -1
                      ) {
                        eventList.push(entity);
                      }
                    }
                  );
                } else {
                  /*
                  // Checking just specific components
                  let changedList = (this.queries[queryName][eventName] = {});
                  event.forEach(component => {
                    let eventList = (changedList[
                      componentPropertyName(component)
                    ] = []);
                    query.eventDispatcher.addEventListener(
                      Query.prototype.COMPONENT_CHANGED,
                      (entity, changedComponent) => {
                        if (
                          changedComponent.constructor === component &&
                          eventList.indexOf(entity) === -1
                        ) {
                          eventList.push(entity);
                        }
                      }
                    );
                  });
                  */
                }
              } else {
                let eventList = (this.queries[queryName][eventName] = []);

                query.eventDispatcher.addEventListener(
                  eventMapping[eventName],
                  (entity) => {
                    // @fixme overhead?
                    if (eventList.indexOf(entity) === -1)
                      eventList.push(entity);
                  }
                );
              }
            }
          });
        }
      }
    }
  }

  stop() {
    this.executeTime = 0;
    this.enabled = false;
  }

  play() {
    this.enabled = true;
  }

  // @question rename to clear queues?
  clearEvents() {
    for (let queryName in this.queries) {
      var query = this.queries[queryName];
      if (query.added) {
        query.added.length = 0;
      }
      if (query.removed) {
        query.removed.length = 0;
      }
      if (query.changed) {
        if (Array.isArray(query.changed)) {
          query.changed.length = 0;
        } else {
          for (let name in query.changed) {
            query.changed[name].length = 0;
          }
        }
      }
    }
  }

  toJSON() {
    var json = {
      name: this.getName(),
      enabled: this.enabled,
      executeTime: this.executeTime,
      priority: this.priority,
      queries: {},
    };

    if (this.constructor.queries) {
      var queries = this.constructor.queries;
      for (let queryName in queries) {
        let query = this.queries[queryName];
        let queryDefinition = queries[queryName];
        let jsonQuery = (json.queries[queryName] = {
          key: this._queries[queryName].key,
        });

        jsonQuery.mandatory = queryDefinition.mandatory === true;
        jsonQuery.reactive =
          queryDefinition.listen &&
          (queryDefinition.listen.added === true ||
            queryDefinition.listen.removed === true ||
            queryDefinition.listen.changed === true ||
            Array.isArray(queryDefinition.listen.changed));

        if (jsonQuery.reactive) {
          jsonQuery.listen = {};

          const methods = ["added", "removed", "changed"];
          methods.forEach((method) => {
            if (query[method]) {
              jsonQuery.listen[method] = {
                entities: query[method].length,
              };
            }
          });
        }
      }
    }

    return json;
  }
}

System.isSystem = true;
System.getName = function () {
  return this.displayName || this.name;
};

export function Not(Component) {
  return {
    operator: "not",
    Component: Component,
  };
}