import { System } from '@serpentity/serpentity';
import { Body, Constraint, SAT, World } from 'matter-js';

import GrabberNode from '../nodes/grabber';
import GrabbableNode from '../nodes/grabbable';

import Config from '../config';

const internals = {
  kGrabRadius: 50,
  kNoEngine: 'No matter js physics engine found. Make sure you set the `engine` key in the config object when initializing.'
};

/**
 * Handles grabbing between entities
 *
 * @extends {external:Serpentity.System}
 * @class GrabSystem
 * @param {object} config a configuration object to extend.
 */
export default class GrabSystem extends System {

  constructor(config = {}) {

    super();

    /**
     * The node collection of grabbers
     *
     * @property {external:Serpentity.NodeCollection} grabbers
     * @instance
     * @memberof GrabSystem
     */
    this.grabbers = null;

    /**
     * The node collection of grabbables
     *
     * @property {external:Serpentity.NodeCollection} grabbables
     * @instance
     * @memberof GrabSystem
     */
    this.grabbables = null;

    /**
     * The matter-js engine we will use to add and remove constraints
     *
     * @property {external:MatterJs.Engine} engine
     * @instance
     * @memberof GrabSystem
     */
    this.engine = config.engine;

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

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

    this.grabbers = engine.getNodes(GrabberNode);
    this.grabbables = engine.getNodes(GrabbableNode);
  }

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

    this.grabbers = null;
    this.grabbables = null;
  }

  /**
   * Runs on every update of the loop. Triggers grab and manages cooldown
   *
   * @function update
   * @instance
   * @param {Number} currentFrameDuration the duration of the current
   * frame
   * @memberof GrabSystem
   */
  update(currentFrameDuration) {

    for (const grabber of this.grabbers) {

      const grab = grabber.grab;

      if (grab.grabbing && !grab.locked) {
        this._grab(grabber);
      }

      const isGrabReleased = !grab.grabbing || grab.currentCooldown >= grab.cooldown;
      if (grab.constraint && isGrabReleased) {
        this._release(grabber);
      }

      if (!grab.grabbing && grab.locked && grab.currentCooldown >= grab.cooldown) {
        this._unlock(grabber);
      }

      if (grab.locked) {
        grab.currentCooldown += currentFrameDuration;
      }

      grab.grabbing = 0;
    }
  }

  // Executes the dash action

  _grab(grabber) {

    const grab = grabber.grab;

    grab.locked = true;
    grab.currentCooldown = 0;

    Body.setPosition(grabber.grabArea.area, grabber.body.body.position);

    for (const grabbable of this.grabbables) {

      if (grabbable.entity === grabber.entity) {
        continue;
      }

      const collision = SAT.collides(grabber.grabArea.area, grabbable.body.body);
      if (collision.collided) {
        grab.constraint = this._createConstraint(grabber.body.body, grabbable.body.body);
      }
    }
  }

  // Executes the unlock action

  _unlock(grabber) {

    grabber.grab.locked = false;
  }

  // Releases a constraint

  _release(grabber) {

    World.remove(this.engine.world, grabber.grab.constraint);
    grabber.grab.currentCooldown = 0;
    grabber.grab.constraint = null;
  }

  // Performs a grab between two entities

  _createConstraint(grabber, grabbable) {

    const constraint = Constraint.create({ // Attach the sensor to the body
      bodyA: grabber,
      bodyB: grabbable,
      damping: 0,
      length: internals.kGrabRadius / Config.meterSize,
      stiffness: 1
    });

    World.add(this.engine.world, [constraint]);

    return constraint;
  }
}