text: import { SteeringBehavior } from '../SteeringBehavior.js';
  import { Path } from '../Path.js';
  import { Vector3 } from '../../math/Vector3.js';
  import { LineSegment } from '../../math/LineSegment.js';
  import { SeekBehavior } from './SeekBehavior.js';
  
  const translation = new Vector3();
  const predictedPosition = new Vector3();
  const normalPoint = new Vector3();
  const lineSegment = new LineSegment();
  const closestNormalPoint = new Vector3();
  
  /**
  * This steering behavior produces a force that keeps a vehicle close to its path. It is intended
  * to use it in combination with {@link FollowPathBehavior} in order to realize a more strict path following.
  *
  * @author {@link https://github.com/Mugen87|Mugen87}
  * @augments SteeringBehavior
  */
  class OnPathBehavior extends SteeringBehavior {
  
  	/**
  	* Constructs a new on path behavior.
  	*
  	* @param {Path} path - The path to stay close to.
  	* @param {Number} radius - Defines the width of the path. With a smaller radius, the vehicle will have to follow the path more closely.
  	* @param {Number} predictionFactor - Determines how far the behavior predicts the movement of the vehicle.
  	*/
  	constructor( path = new Path(), radius = 0.1, predictionFactor = 1 ) {
  
  		super();
  
  		/**
  		* The path to stay close to.
  		* @type {Path}
  		*/
  		this.path = path;
  
  		/**
  		* Defines the width of the path. With a smaller radius, the vehicle will have to follow the path more closely.
  		* @type {Number}
  		* @default 0.1
  		*/
  		this.radius = radius;
  
  		/**
  		* Determines how far the behavior predicts the movement of the vehicle.
  		* @type {Number}
  		* @default 1
  		*/
  		this.predictionFactor = predictionFactor;
  
  		// internal behaviors
  
  		this._seek = new SeekBehavior();
  
  	}
  
  	/**
  	* Calculates the steering force for a single simulation step.
  	*
  	* @param {Vehicle} vehicle - The game entity the force is produced for.
  	* @param {Vector3} force - The force/result vector.
  	* @param {Number} delta - The time delta.
  	* @return {Vector3} The force/result vector.
  	*/
  	calculate( vehicle, force /*, delta */ ) {
  
  		const path = this.path;
  
  		// predicted future position
  
  		translation.copy( vehicle.velocity ).multiplyScalar( this.predictionFactor );
  		predictedPosition.addVectors( vehicle.position, translation );
  
  		// compute closest line segment and normal point. the normal point is computed by projecting
  		// the predicted position of the vehicle on a line segment.
  
  		let minDistance = Infinity;
  
  		let l = path._waypoints.length;
  
  		// handle looped paths differently since they have one line segment more
  
  		l = ( path.loop === true ) ? l : l - 1;
  
  		for ( let i = 0; i < l; i ++ ) {
  
  			lineSegment.from = path._waypoints[ i ];
  
  			// the last waypoint needs to be handled differently for a looped path.
  			// connect the last point with the first one in order to create the last line segment
  
  			if ( path.loop === true && i === ( l - 1 ) ) {
  
  				lineSegment.to = path._waypoints[ 0 ];
  
  			} else {
  
  				lineSegment.to = path._waypoints[ i + 1 ];
  
  			}
  
  			lineSegment.closestPointToPoint( predictedPosition, true, normalPoint );
  
  			const distance = predictedPosition.squaredDistanceTo( normalPoint );
  
  			if ( distance < minDistance ) {
  
  				minDistance = distance;
  				closestNormalPoint.copy( normalPoint );
  
  			}
  
  		}
  
  		// seek towards the projected point on the closest line segment if
  		// the predicted position of the vehicle is outside the valid range.
  		// also ensure that the path length is greater than zero when performing a seek
  
  		if ( minDistance > ( this.radius * this.radius ) && path._waypoints.length > 1 ) {
  
  			this._seek.target = closestNormalPoint;
  			this._seek.calculate( vehicle, force );
  
  		}
  
  		return force;
  
  	}
  
  	/**
  	* Transforms this instance into a JSON object.
  	*
  	* @return {Object} The JSON object.
  	*/
  	toJSON() {
  
  		const json = super.toJSON();
  
  		json.path = this.path.toJSON();
  		json.radius = this.radius;
  		json.predictionFactor = this.predictionFactor;
  
  		return json;
  
  	}
  
  	/**
  	* Restores this instance from the given JSON object.
  	*
  	* @param {Object} json - The JSON object.
  	* @return {OnPathBehavior} A reference to this behavior.
  	*/
  	fromJSON( json ) {
  
  		super.fromJSON( json );
  
  		this.path.fromJSON( json.path );
  		this.radius = json.radius;
  		this.predictionFactor = json.predictionFactor;
  
  		return this;
  
  	}
  
  }
  
  export { OnPathBehavior };
  