use nalgebra::{DVector, RowDVector};

use crate::algebra::distance_field::DistanceField;
use crate::algebra::subspace::{Line, Subspace};
use crate::algebra::{Point, Scalar, N};
use crate::particle_system::ParticleSystem;

use super::Constraint;

/// Keep a particle at certain distance within distance field
pub struct DistanceConstraint<D: DistanceField> {
    particle_id: usize,
    distance_field: D,
    distance: Scalar,
}

impl ParticleSystem {
    pub fn add_distance_constraint<const DIM: usize>(&mut self, particle_id: usize, subspace: Subspace<DIM>, distance: Scalar) {
        let particle = &self.particles[particle_id];

        self.constraints.push(Box::new(DistanceConstraint {
            particle_id,
            distance,
            distance_field: subspace,
        }));
    }
}

impl<D: DistanceField> Constraint for DistanceConstraint<D> {
    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);

        self.distance_field.distance(Point::from_coordinates(position.into())) - self.distance
    }

    fn jacobian(&self, q: &DVector<Scalar>) -> RowDVector<Scalar> {
        let point = Point::from_coordinates(q.fixed_rows::<N>(self.particle_id * N).into());
        let normal = self.distance_field.project_point(point) - point;

        let mut result = RowDVector::zeros(q.len());
        for i in 0..N {
            result[self.particle_id * N + i] = normal[i];
        }
        result
    }
}