From ec2647b8696dad6844a448d29af485b862ec6841 Mon Sep 17 00:00:00 2001
From: Rutherther <rutherther@ditigal.xyz>
Date: Sat, 1 Nov 2025 12:43:48 +0100
Subject: [PATCH] feat(lib): add roulette wheel selection

---
 codes/eoa_lib/src/selection.rs | 50 +++++++++++++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/codes/eoa_lib/src/selection.rs b/codes/eoa_lib/src/selection.rs
index 0c497f445f2e07f5bbc476e3ab80c3ea2fa68c70..ca1e4f6f8527afea0f831b15c1cb7885bf1df69b 100644
--- a/codes/eoa_lib/src/selection.rs
+++ b/codes/eoa_lib/src/selection.rs
@@ -1,5 +1,7 @@
+use nalgebra::{Dyn, OVector, Scalar, U1};
 use rand::{seq::IteratorRandom, Rng, RngCore};
-use std::fmt::Debug;
+use rand_distr::uniform::{SampleRange, SampleUniform};
+use std::{cmp::Ordering, fmt::Debug, ops::{AddAssign, Sub}};
 
 use crate::{comparison::BetterThanOperator, replacement::EvaluatedPopulation};
 
@@ -108,3 +110,49 @@ impl<TChromosome, TResult: Copy + Debug> Selection<TChromosome, TResult> for Tou
         })
     }
 }
+
+
+pub struct RouletteWheelSelection;
+impl RouletteWheelSelection {
+    pub fn new() -> Self {
+        Self
+    }
+}
+
+impl<TChromosome,
+     TResult: Scalar + Copy + Default + PartialOrd + SampleUniform + AddAssign + Sub<Output = TResult>>
+    Selection<TChromosome, TResult> for RouletteWheelSelection
+{
+    fn select(
+        &self,
+        count: usize,
+        evaluations: &EvaluatedPopulation<TChromosome, TResult>,
+        _: &dyn BetterThanOperator<TResult>,
+        rng: &mut dyn RngCore
+    ) -> impl Iterator<Item = usize> {
+        let zero: TResult = Default::default();
+        let max = evaluations.iter()
+            .map(|i| i.evaluation)
+            .max_by(|a, b|
+                    a.partial_cmp(b).unwrap_or(Ordering::Less))
+            .unwrap();
+        let summed = evaluations.iter().scan(
+            zero,
+            |acc, individual| {
+                let subtracted: TResult = max - individual.evaluation;
+                *acc += subtracted;
+                Some(*acc)
+            })
+            .collect::<Vec<TResult>>();
+        let max = summed.last().unwrap().clone();
+
+        (0..count).map(move |_| {
+            let rand = rng.random_range(zero..=max);
+
+            (0..summed.len())
+                .filter(|&i| summed[i] > rand)
+                .next()
+                .unwrap_or(summed.len() - 1)
+        })
+    }
+}