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use nalgebra::{distance_squared, Point3};
use super::super::{HasSteeringBehavior, SteeringAcceleration, SteeringAccelerationCalculator,
                   SteeringBehavior};
use alga::general::Real;
use alga::general::AbstractModule;
use std::cell::RefMut;
use std::cell::RefCell;
use std::rc::Rc;

///Pursue behaviour aims to steer the agent towards target by predicting
///where target will be in time t. Steering calculation is based on targets
///future position. It is like aiming at a moving target.
#[builder(pattern = "immutable")]
#[derive(Builder)]
pub struct Pursue<T>
where
    T: Real,
{
    /// Common behavior attributes
    pub behavior: RefCell<SteeringBehavior<T>>,

    pub max_prediction_time: T,
}


impl<T: Real> HasSteeringBehavior<T> for Pursue<T> {
    fn get_steering_behavior(&mut self) -> RefMut<SteeringBehavior<T>> {
        self.behavior.borrow_mut()
    }
}

impl<T: Real> SteeringAccelerationCalculator<T> for Pursue<T> {
    fn calculate_real_steering(
        &self,
        steering_acceleration: Rc<RefCell<SteeringAcceleration<T>>>,
    ) -> Rc<RefCell<SteeringAcceleration<T>>> {
        let behavior = self.behavior.borrow();
        let square_distance = distance_squared(
            &Point3::from_coordinates(
                *behavior.target.borrow().get_position() -
                    *behavior.owner.borrow().get_position(),
            ),
            &Point3::origin(),
        );
        let square_speed =
            distance_squared(
                &Point3::from_coordinates(*behavior.owner.borrow().get_linear_velocity()),
                &Point3::origin(),
            );
        let mut prediction_time = self.max_prediction_time;
        if square_speed > T::zero() {
            let square_prediction_time = square_distance / square_speed;
            if square_prediction_time < self.max_prediction_time * self.max_prediction_time {
                prediction_time = square_prediction_time.sqrt();
            }
        }

        steering_acceleration.borrow_mut().linear = *behavior.target.borrow().get_position();
        steering_acceleration.borrow_mut().mul_add(
            SteeringAcceleration::new(
                *behavior.target.borrow().get_linear_velocity(),
                T::zero(),
            ),
            prediction_time,
        );
        let mut sa = steering_acceleration.borrow_mut();
        sa.linear -= *behavior.owner.borrow().get_position();
        sa.linear = sa.linear.normalize();
        sa.linear = sa.linear.multiply_by(match self.behavior.borrow().limiter {
            Some(ref a) => (*a).borrow().get_max_linear_acceleration(),
            None => T::one(),
        });
        sa.angular = T::zero();
        steering_acceleration.clone()
    }
}