From d4df3887a92f94774475ea5fafb33408e1ba10a7 Mon Sep 17 00:00:00 2001
From: Rutherther <rutherther@ditigal.xyz>
Date: Sun, 26 Oct 2025 21:42:21 +0100
Subject: [PATCH] feat: add pairing of parents

---
 env/src/main.rs    |  1 +
 env/src/pairing.rs | 67 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+)
 create mode 100644 env/src/pairing.rs

diff --git a/env/src/main.rs b/env/src/main.rs
index 1a9fa9efd93412a9f642460bd2af37b8228b38de..50c14dcd56cc4247be9641df42ce074d2a2f2f0d 100644
--- a/env/src/main.rs
+++ b/env/src/main.rs
@@ -1,4 +1,5 @@
 pub mod fitness;
+pub mod pairing;
 pub mod crossover;
 pub mod bounded;
 pub mod selection;
diff --git a/env/src/pairing.rs b/env/src/pairing.rs
new file mode 100644
index 0000000000000000000000000000000000000000..4d71f157c4cb6a2054b3955a9bfb00ebf6d2f238
--- /dev/null
+++ b/env/src/pairing.rs
@@ -0,0 +1,67 @@
+use std::marker::PhantomData;
+
+use crate::replacement::EvaluatedPopulation;
+
+pub type ParentPairing = (usize, usize);
+
+pub trait Pairing {
+    type Chromosome;
+    type Out;
+
+    fn pair<T: Iterator<Item = usize>>(
+        &mut self,
+        population: &EvaluatedPopulation<Self::Chromosome, Self::Out>,
+        parents: T
+    ) -> impl Iterator<Item = ParentPairing>;
+}
+
+pub struct AdjacentPairing<TChromosome, TOutput> {
+    _phantom1: PhantomData<TChromosome>,
+    _phantom2: PhantomData<TOutput>,
+}
+
+impl<TChromosome, TOutput> AdjacentPairing<TChromosome, TOutput> {
+    pub fn new() -> Self {
+        Self {
+            _phantom1: PhantomData,
+            _phantom2: PhantomData,
+        }
+    }
+}
+
+impl<TChromosome, TOutput> Pairing for AdjacentPairing<TChromosome, TOutput> {
+    type Chromosome = TChromosome;
+    type Out = TOutput;
+
+    fn pair<T: Iterator<Item = usize>>(
+        &mut self,
+        _: &EvaluatedPopulation<Self::Chromosome, Self::Out>,
+        parents: T
+    ) -> impl Iterator<Item = ParentPairing> {
+        AdjacentIterator(parents, 0)
+    }
+}
+
+pub struct AdjacentIterator<T: Iterator<Item = usize>>(T, usize);
+
+impl<T: Iterator<Item = usize>> Iterator for AdjacentIterator<T> {
+    type Item = ParentPairing;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let first = self.0.next();
+        let second = self.0.next();
+
+        match (first, second) {
+            // Still two elements left, return them
+            (Some(first), Some(second)) => {
+                self.1 = second; // Save previous
+                Some((first, second))
+            },
+            // Only one element remaining, return it and the previous one
+            (Some(first), _) => Some((first, self.1)),
+            (None, Some(_)) => panic!("Iterators cannot return something after they return none."),
+            // No more elements
+            _ => None
+        }
+    }
+}