import { Entity } from './Entity.ts';
import type { Engine } from './Engine.ts';

/**
 * Base System class for ECS architecture.
 * Systems contain logic that operates on entities with specific components.
 */
export class System {
  /** Unique identifier for the system */
  readonly name: string;

  /** List of component types required by this system */
  requiredComponents: string[];

  /** Execution priority (lower runs first) */
  priority: number;

  /** Reference to the game engine */
  protected engine!: Engine;

  /**
   * @param name - The unique name of the system
   */
  constructor(name: string) {
    this.name = name;
    this.requiredComponents = [];
    this.priority = 0;
  }

  /**
   * Check if an entity matches this system's requirements.
   * @param entity - The entity to check
   * @returns True if the entity is active and has all required components
   */
  matches(entity: Entity): boolean {
    if (!entity.active) return false;
    return this.requiredComponents.every((componentType) => entity.hasComponent(componentType));
  }

  /**
   * Main update entry point called every frame.
   * @param deltaTime - Time elapsed since last frame in seconds
   * @param entities - All entities in the engine
   */
  update(deltaTime: number, entities: Entity[]): void {
    const matchingEntities = entities.filter((entity) => this.matches(entity));
    this.process(deltaTime, matchingEntities);
  }

  /**
   * Process matching entities. To be implemented by subclasses.
   * @param _deltaTime - Time elapsed since last frame in seconds
   * @param _entities - Filtered entities that match this system
   */
  process(_deltaTime: number, _entities: Entity[]): void {}

  /**
   * Called when system is added to engine.
   * @param engine - The game engine instance
   */
  init(engine: Engine): void {
    this.engine = engine;
  }
}