use std::convert::Infallible;

use nalgebra::SVector;
use rand_distr::{Normal, NormalError};

use crate::{local_search::{LocalSearchCandidate, LocalSearchStats}, perturbation::{BoundedPerturbation, PerturbationOperator, RandomDistributionPerturbation}};

pub trait EvolutionaryStrategy<TOut, TPerturbation: PerturbationOperator> {
    type Err;

    fn step(&mut self,
            perturbation: &mut TPerturbation,
            better: bool,
            stats: &LocalSearchStats<TPerturbation::Chromosome, TOut>
    ) -> Result<(), Self::Err>;
}

fn normal_one_to_five<const LEN: usize>(perturbation: &mut RandomDistributionPerturbation<LEN, Normal<f64>>, better: bool) -> Result<(), NormalError> {
    let exp: f64 = if better { 1.0 } else { 0.0 } - 0.2;
    let sigma = perturbation.std_dev();

    let new_sigma = sigma * exp.exp().powf(1.0 / LEN as f64);

    perturbation.set_std_dev(new_sigma)?;
    Ok(())
}

pub struct OneToFiveStrategy;
impl<const LEN: usize, TOut> EvolutionaryStrategy<TOut, RandomDistributionPerturbation<LEN, Normal<f64>>> for OneToFiveStrategy {
    type Err = NormalError;

    fn step(&mut self,
            perturbation: &mut RandomDistributionPerturbation<LEN, Normal<f64>>,
            better: bool,
            _: &LocalSearchStats<SVector::<f64, LEN>, TOut>
    ) -> Result<(), Self::Err> {
        normal_one_to_five(perturbation, better)
    }
}

// TODO: I don't really like this to be honest. This would basically have to take care of any perturbation wrapper
// that there is. But that just seems wrong.
impl<const LEN: usize, TOut> EvolutionaryStrategy<TOut, BoundedPerturbation<LEN, RandomDistributionPerturbation<LEN, Normal<f64>>>> for OneToFiveStrategy {
    type Err = NormalError;

    fn step(&mut self,
            perturbation: &mut BoundedPerturbation<LEN, RandomDistributionPerturbation<LEN, Normal<f64>>>,
            better: bool,
            _: &LocalSearchStats<<BoundedPerturbation<LEN, RandomDistributionPerturbation<LEN, Normal<f64>>> as PerturbationOperator>::Chromosome, TOut>
    ) -> Result<(), Self::Err> {
        normal_one_to_five(perturbation.inner_mut(), better)
    }
}

pub struct IdentityStrategy;
impl<TOut, TPerturbation: PerturbationOperator> EvolutionaryStrategy<TOut, TPerturbation> for IdentityStrategy {
    type Err = Infallible;

    fn step(&mut self,
            _: &mut TPerturbation,
            _: bool,
            _: &LocalSearchStats<TPerturbation::Chromosome, TOut>
    ) -> Result<(), Self::Err> {
        Ok(())
    }
}