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use crate::Kernel;
use std::ops::Add;

impl<T> Add<Kernel<T>> for Kernel<T>
where
    T: 'static + ?Sized,
{
    type Output = Self;

    fn add(self, rhs: Kernel<T>) -> Self::Output {
        let self_params_len = self.params.len();

        let params = [&self.params as &[f64], &rhs.params as &[f64]].concat();

        let self_func = self.func;
        let rhs_func = rhs.func;

        Self {
            params,
            func: Box::new(move |x: &T, x_prime: &T, with_grad: bool, params: &[f64]| {
                let (fx, dfx) = self_func(x, x_prime, with_grad, &params[..self_params_len])?;
                let (gx, dgx) = rhs_func(x, x_prime, with_grad, &params[self_params_len..])?;

                let func = fx + gx;

                let grad = if !with_grad {
                    None
                } else {
                    let grad = [dfx.unwrap(), dgx.unwrap()].concat();

                    Some(grad)
                };

                Ok((func, grad))
            }),
        }
    }
}