use nalgebra::{DVector, RowDVector};

use crate::particle_system::{ParticleSystem, Point, Scalar, N};

use super::Constraint;

pub struct AnchorConstraint {
    pub particle_id: usize,
    pub anchor: Point,

    jacobian: RowDVector<Scalar>,
}

impl ParticleSystem {
    pub fn add_anchor_constraint(&mut self, particle_id: usize) {
        let anchor = self.particles[particle_id].position;
        self.constraints.push(Box::new(AnchorConstraint {
            particle_id,
            anchor,
            jacobian: RowDVector::zeros(self.particles.len() * N),
        }));
    }
}

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

    fn c(&self, q: &DVector<Scalar>) -> Scalar {
        let position = q.fixed_rows(self.particle_id * N);
        (position - self.anchor.coords).norm()
    }

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

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