src/engine/Game.ts


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import { Entity } from "./entities";
import { System } from "./systems";

export class Game {
  private systemOrder: string[];

  private running: boolean;
  private lastTimeStamp: number;

  public entities: Map<string, Entity>;
  public systems: Map<string, System>;
  public componentEntities: Map<string, Set<string>>;

  constructor() {
    this.lastTimeStamp = performance.now();
    this.running = false;
    this.systemOrder = [];
    this.systems = new Map();
    this.entities = new Map();
    this.componentEntities = new Map();
  }

  public resetState() {
    this.entities.clear();
    this.componentEntities.clear();
  }

  public start() {
    this.lastTimeStamp = performance.now();
    this.running = true;
  }

  public stop() {
    this.running = false;
  }

  public addEntity(entity: Entity) {
    this.entities.set(entity.id, entity);
  }

  public getEntity(id: string): Entity | undefined {
    return this.entities.get(id);
  }

  public removeEntity(id: string) {
    this.entities.delete(id);
  }

  public forEachEntityWithComponent(
    componentName: string,
    callback: (entity: Entity) => void
  ) {
    this.componentEntities.get(componentName)?.forEach((entityId) => {
      const entity = this.getEntity(entityId);
      if (!entity) return;

      callback(entity);
    });
  }

  public addSystem(system: System) {
    if (!this.systemOrder.includes(system.name)) {
      this.systemOrder.push(system.name);
    }
    this.systems.set(system.name, system);
  }

  public getSystem<T>(name: string): T {
    return this.systems.get(name) as unknown as T;
  }

  public doGameLoop(timeStamp: number) {
    if (!this.running) {
      return;
    }

    const dt = timeStamp - this.lastTimeStamp;
    this.lastTimeStamp = timeStamp;

    // rebuild the Component -> { Entity } map
    this.componentEntities.clear();
    this.entities.forEach((entity) =>
      entity.getComponents().forEach((component) => {
        if (!this.componentEntities.has(component.name)) {
          this.componentEntities.set(
            component.name,
            new Set<string>([entity.id])
          );
          return;
        }
        this.componentEntities.get(component.name)?.add(entity.id);
      })
    );

    this.systemOrder.forEach((systemName) => {
      this.systems.get(systemName)?.update(dt, this);
    });
  }
}