use std::marker::PhantomData;

use alga::linear::Translation;
use math::{Isometry, Point};
use geometry::shape::{Ball, Shape};
use geometry::query::{Contact, ContactPrediction};
use geometry::query::contacts_internal;
use narrow_phase::{ContactDispatcher, ContactGenerator};

/// Collision detector between two balls.
pub struct BallBallContactGenerator<P: Point, M> {
    contact: Option<Contact<P>>,
    mat_type: PhantomData<M>, // FIXME: can we avoid this?
}

impl<P: Point, M> Clone for BallBallContactGenerator<P, M> {
    fn clone(&self) -> BallBallContactGenerator<P, M> {
        BallBallContactGenerator {
            contact: self.contact.clone(),
            mat_type: PhantomData,
        }
    }
}

impl<P: Point, M> BallBallContactGenerator<P, M> {
    /// Creates a new persistent collision detector between two balls.
    #[inline]
    pub fn new() -> BallBallContactGenerator<P, M> {
        BallBallContactGenerator {
            contact: None,
            mat_type: PhantomData,
        }
    }
}

impl<P: Point, M: Isometry<P>> ContactGenerator<P, M> for BallBallContactGenerator<P, M> {
    fn update(
        &mut self,
        _: &ContactDispatcher<P, M>,
        ma: &M,
        a: &Shape<P, M>,
        mb: &M,
        b: &Shape<P, M>,
        prediction: &ContactPrediction<P::Real>,
    ) -> bool {
        if let (Some(a), Some(b)) = (a.as_shape::<Ball<P::Real>>(), b.as_shape::<Ball<P::Real>>()) {
            self.contact = contacts_internal::ball_against_ball(
                &P::from_coordinates(ma.translation().to_vector()),
                a,
                &P::from_coordinates(mb.translation().to_vector()),
                b,
                prediction.linear,
            );

            true
        } else {
            false
        }
    }

    #[inline]
    fn num_contacts(&self) -> usize {
        match self.contact {
            None => 0,
            Some(_) => 1,
        }
    }

    #[inline]
    fn contacts(&self, out_contacts: &mut Vec<Contact<P>>) {
        match self.contact {
            Some(ref c) => out_contacts.push(c.clone()),
            None => (),
        }
    }
}