import { System } from '@serpentity/serpentity';

const internals = {
  kTightStiffness: 0.001,
  kBaseStiffness: 0.0008,
  kLooseStiffness: 0.0000001
};

import ElasticNode from '../nodes/elastic';

/**
 Changes the stiffness on the node when it's less extended
 *
 * @extends {external:Serpentity.System}
 * @class ElasticSystem
 * @param {object} config a configuration object to extend.
 */
export default class ElasticSystem extends System {

  constructor(config = {}) {

    super();

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

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

    this.elastics = engine.getNodes(ElasticNode);
  }

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

    this.elastics = null;
  }

  /**
   * Runs on every update of the loop. Checks length of elastic and adjusts
   * stiffness
   *
   * @function update
   * @instance
   * @param {Number} currentFrameDuration the duration of the current
   * frame
   * @memberof ElasticSystem
   */
  update(currentFrameDuration) {

    for (const elastic of this.elastics) {
      const constraint = elastic.body.body;

      const currentDistance = Math.abs(
        Math.sqrt(
          Math.pow(constraint.bodyA.position.x - constraint.bodyB.position.x, 2) +
          Math.pow(constraint.bodyA.position.y - constraint.bodyB.position.y, 2)));

      if (currentDistance <= constraint.length) {
        constraint.stiffness = internals.kLooseStiffness;
        continue;
      }

      if (currentDistance >= 2.6 * constraint.length) {
        constraint.stiffness = internals.kTightStiffness;
        continue;
      }

      constraint.stiffness = internals.kBaseStiffness;
    }
  }
}