radiate-alters 1.2.22

use radiate_core::{
    AlterContext, AlterResult, ArithmeticGene, Chromosome, Crossover, Rate, Valid, random_provider,
};

/// The [MeanCrossover] is a simple crossover method that replaces the genes of the first chromosome
/// with the mean of the two genes. The mean is calculated by adding the two genes together and dividing
/// by two.
///
/// This crossover can only be used with [ArithmeticGene]`s and can be largely benifitial. However, keep
/// in mind that because we are taking the mean of two genes, this results in children that
/// converge towards a common distribution. This can be useful in some cases, but it can also
/// result in a loss of diversity in the population in others.
pub struct MeanCrossover {
    rate: Rate,
}

impl MeanCrossover {
    /// Create a new instance of the `MeanCrossover` with the given rate.
    /// The rate must be between 0.0 and 1.0.
    pub fn new(rate: impl Into<Rate>) -> Self {
        let rate = rate.into();

        if !rate.is_valid() {
            panic!("Rate {rate:?} is not valid. Must be between 0.0 and 1.0",);
        }

        MeanCrossover { rate }
    }
}

impl<C: Chromosome> Crossover<C> for MeanCrossover
where
    C::Gene: ArithmeticGene,
{
    fn rate(&self) -> Rate {
        self.rate.clone()
    }

    #[inline]
    fn cross_chromosomes(
        &self,
        chrom_one: &mut C,
        chrom_two: &mut C,
        ctx: &mut AlterContext,
    ) -> AlterResult {
        let mut count = 0;

        random_provider::with_rng(|rand| {
            for (gene_one, gene_two) in chrom_one.iter_mut().zip(chrom_two.iter()) {
                if rand.bool(ctx.rate()) {
                    *gene_one = gene_one.mean(gene_two);
                    count += 1;
                }
            }
        });

        count.into()
    }
}