import { Scene } from '../Scene';
import { World } from './World';
/**
 * Enum that determines whether to run the system in the update or draw phase
 */
export declare enum SystemType {
    Update = "update",
    Draw = "draw"
}
/**
 * An Excalibur {@apilink System} that updates entities of certain types.
 * Systems are scene specific
 *
 *
 *
 * Excalibur Systems currently require at least 1 Component type to operated
 *
 * Multiple types are declared as a type union
 * For example:
 *
 * ```typescript
 * class MySystem extends System {
 *   static priority = SystemPriority.Lowest;
 *   public readonly systemType = SystemType.Update;
 *   public query: Query<typeof TransformComponent>;
 *   constructor(public world: World) {
 *   super();
 *      this.query = this.world.query([TransformComponent]);
 *   }
 *   public update(elapsed: number) {
 *      ...
 *   }
 * }
 * ```
 */
export declare abstract class System {
    /**
     * Determine whether the system is called in the {@apilink SystemType.Update} or the {@apilink SystemType.Draw} phase. Update is first, then Draw.
     */
    abstract readonly systemType: SystemType;
    /**
     * System can execute in priority order, by default all systems are priority 0. Lower values indicated higher priority.
     * For a system to execute before all other a lower priority value (-1 for example) must be set.
     * For a system to execute after all other a higher priority value (10 for example) must be set.
     */
    static priority: number;
    /**
     * Optionally specify an initialize handler
     * @param scene
     */
    initialize?(world: World, scene: Scene): void;
    /**
     * Update all entities that match this system's types
     * @param elapsed Time in milliseconds
     */
    abstract update(elapsed: number): void;
    /**
     * Optionally run a preupdate before the system processes matching entities
     * @param scene
     * @param elapsed Time in milliseconds since the last frame
     */
    preupdate?(scene: Scene, elapsed: number): void;
    /**
     * Optionally run a postupdate after the system processes matching entities
     * @param scene
     * @param elapsed Time in milliseconds since the last frame
     */
    postupdate?(scene: Scene, elapsed: number): void;
}