import { System } from '@serpentity/serpentity';
import { Body, Vector } from 'matter-js';

const internals = {
  kForce: 0.0001
};

import PhysicalWithExternalForceNode from '../nodes/physical_with_external_force';

/**
 * Applies physica from external forces (eg. controls) to the physics body
 *
 * @extends {external:Serpentity.System}
 * @class ApplyForceSystem
 * @param {object} config a configuration object to extend.
 */
export default class ApplyForceSystem extends System {

  constructor(config = {}) {

    super();

    /**
     * The node collection of entities that have external force
     *
     * @property {external:Serpentity.NodeCollection} physicalEntities
     * @instance
     * @memberof ApplyForceSystem
     */
    this.physicalEntities = null;
  }

  /**
   * Initializes system when added. Requests physics nodes
   *
   * @function added
   * @memberof ApplyForceSystem
   * @instance
   * @param {external:Serpentity.Engine} engine the serpentity engine to
   * which we are getting added
   */
  added(engine) {

    this.physicalEntities = engine.getNodes(PhysicalWithExternalForceNode);
  }

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

    this.physicalEntities = null;
  }

  /**
   * Runs on every update of the loop. Updates the body based on the force
   * component
   *
   * @function update
   * @instance
   * @param {Number} currentFrameDuration the duration of the current
   * frame
   * @memberof ApplyForceSystem
   */
  update(currentFrameDuration) {

    for (const physicalEntity of this.physicalEntities) {
      const body = physicalEntity.body.body;
      const force = physicalEntity.force;
      const forceVector = Vector.create(force.x * internals.kForce, force.y * internals.kForce);


      // Store the last angle and apply force on non-zero forces

      if (force.x || force.y) {
        force.lastAngle = Math.atan2(force.y, force.x);
        Body.applyForce(body,
          {
            x: body.position.x,
            y: body.position.y
          },
          forceVector
        );
      }

      // Reset the force

      force.x = 0;
      force.y = 0;
    }
  }
}