use nalgebra::{DVector, RowDVector};

use crate::{
    algebra::{subspace::Line, Point, Scalar, Vector, N},
    particle_system::ParticleSystem,
};

use super::Constraint;

pub struct SliderConstraint {
    pub particle_id: usize,

    pub line: Line,

    jacobian: RowDVector<Scalar>,
}

impl ParticleSystem {
    pub fn add_slider_constraint(&mut self, particle_id: usize, direction: Vector) {
        let point = self.particles[particle_id].position;
        self.constraints.push(Box::new(SliderConstraint {
            particle_id,
            line: Line::new(point, [direction]),
            jacobian: RowDVector::zeros(self.particles.len() * N),
        }));
    }
}

impl Constraint for SliderConstraint {
    fn get_particles(&self) -> Vec<usize> {
        vec![self.particle_id]
    }

    fn c(&self, q: &DVector<Scalar>) -> Scalar {
        let position = q.fixed_rows::<N>(self.particle_id * N);
        let point = Point::from_coordinates(position.into());
        self.line.distance(point)
    }

    fn set_jacobian(&mut self, jacobian: RowDVector<Scalar>) {
        self.jacobian = jacobian
    }

    fn jacobian_prev(&self) -> RowDVector<Scalar> {
        self.jacobian.clone()
    }
}