import { System } from '@serpentity/serpentity';
import { Engine, World } from 'matter-js';

import PhysicalNode from '../nodes/physical';
import GrabAreaNode from '../nodes/grab_area';

const internals = {
  kNoEngine: 'No matter js physics engine found. Make sure you set the `engine` key in the config object when initializing.'
};

/**
 * Adds and removes objects to the physics world and calls update
 *
 * @extends {external:Serpentity.System}
 * @class PhysicsWorldControlSystem
 * @param {object} config a configuration object to extend.
 */
export default class PhysicsWorldControlSystem extends System {

  constructor(config = {}) {

    super();

    /**
     * The node collection of physics entities
     *
     * @property {external:Serpentity.NodeCollection} physicalEntities
     * @instance
     * @memberof PhysicsWorldControlSystem
     */
    this.physicalEntities = null;

    /**
     * The matter-js engine we will use to process physics
     *
     * @property {external:MatterJs.Engine} engine
     * @instance
     * @memberof PhysicsWorldControlSystem
     */
    this.engine = config.engine;

    if (!this.engine) {
      throw new Error(internals.kNoEngine);
    }
  }

  /**
   * Initializes system when added. Requests physics nodes and
   * attaches to event listeners to add / remove them to pixi stage
   *
   * @function added
   * @memberof PhysicsWorldControlSystem
   * @instance
   * @param {external:Serpentity.Engine} engine the serpentity engine to
   * which we are getting added
   */
  added(engine) {

    this.physicalEntities = engine.getNodes(PhysicalNode);
    this.grabAreaEntities = engine.getNodes(GrabAreaNode);

    this.physicalEntities.on('nodeAdded', (event) => {

      World.add(this.engine.world, [event.node.body.body]);
    });
    this.physicalEntities.on('nodeRemoved', (event) => {

      World.remove(this.engine.world, [event.node.body.body]);
    });

    this.grabAreaEntities.on('nodeAdded', (event) => {

      World.add(this.engine.world, [event.node.grabArea.area]);
    });
    this.grabAreaEntities.on('nodeRemoved', (event) => {

      World.remove(this.engine.world, [event.node.grabArea.area]);
    });
  }

  /**
   * Clears system resources when removed.
   *
   * @function removed
   * @instance
   * @memberof PhysicsWorldControlSystem
   */
  removed() {

    this.physicalEntities.removeAllListeners('nodeAdded');
    this.physicalEntities.removeAllListeners('nodeRemoved');
    this.physicalEntities = null;

    this.grabAreaEntities.removeAllListeners('nodeAdded');
    this.grabAreaEntities.removeAllListeners('nodeRemoved');
    this.grabAreaEntities = null;
  }

  /**
   * Runs on every update of the loop. Updates the physics
   *
   * @function update
   * @instance
   * @param {Number} currentFrameDuration the duration of the current
   * frame
   * @memberof PhysicsWorldControlSystem
   */
  update(currentFrameDuration) {

    Engine.update(this.engine, currentFrameDuration);
  }
}