use ndarray::prelude::*;

use super::Kernel;

pub struct Constant {
    var: f64,
}

impl Constant {
    pub fn new(var: f64) -> Self {
        Constant { var }
    }
}

impl Kernel for Constant {
    fn k_diag(&self, ts: &[f64]) -> Array1<f64> {
        Array1::ones(ts.len()) * self.var
    }

    fn order(&self) -> usize {
        1
    }

    fn state_mean(&self, _t: f64) -> Array1<f64> {
        Array1::zeros(1)
    }

    fn state_cov(&self, _t: f64) -> Array2<f64> {
        array![[1.0]] * self.var
    }

    fn measurement_vector(&self) -> Array1<f64> {
        array![1.0]
    }

    fn feedback(&self) -> Array2<f64> {
        array![[0.0]]
    }

    fn transition(&self, _t0: f64, _t1: f64) -> Array2<f64> {
        array![[1.0]]
    }

    fn noise_cov(&self, _t0: f64, _t1: f64) -> Array2<f64> {
        array![[0.0]]
    }
}