From 2a1ccd5e3c66b01084db4612ea5f43b737e64e6d Mon Sep 17 00:00:00 2001
From: Kyle Barron <kyle@developmentseed.org>
Date: Mon, 6 Jan 2025 11:28:55 -0500
Subject: [PATCH 1/2] Return opaque iterator for nearest neighbor searches

---
 src/rtree/trait.rs | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/rtree/trait.rs b/src/rtree/trait.rs
index d621c69..aeaa3d2 100644
--- a/src/rtree/trait.rs
+++ b/src/rtree/trait.rs
@@ -151,7 +151,7 @@ pub trait RTreeIndex<N: IndexableNum>: Sized {
         y: N,
         max_results: Option<usize>,
         max_distance: Option<N>,
-    ) -> Vec<u32> {
+    ) -> impl Iterator<Item = u32> {
         let boxes = self.boxes();
         let indices = self.indices();
         let max_distance = max_distance.unwrap_or(N::max_value());
@@ -212,7 +212,7 @@ pub trait RTreeIndex<N: IndexableNum>: Sized {
             }
         }
 
-        results
+        results.into_iter()
     }
 
     /// Search items in order of distance from the given coordinate.
@@ -221,7 +221,7 @@ pub trait RTreeIndex<N: IndexableNum>: Sized {
         coord: &impl CoordTrait<T = N>,
         max_results: Option<usize>,
         max_distance: Option<N>,
-    ) -> Vec<u32> {
+    ) -> impl Iterator<Item = u32> {
         self.neighbors(coord.x(), coord.y(), max_results, max_distance)
     }
 

From 6732689edd679c67d866620e6a47cee65d4cdcc0 Mon Sep 17 00:00:00 2001
From: Kyle Barron <kyle@developmentseed.org>
Date: Mon, 6 Jan 2025 11:58:14 -0500
Subject: [PATCH 2/2] wip: try to convert to iterator

---
 src/rtree/trait.rs | 67 +++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 60 insertions(+), 7 deletions(-)

diff --git a/src/rtree/trait.rs b/src/rtree/trait.rs
index aeaa3d2..d82d354 100644
--- a/src/rtree/trait.rs
+++ b/src/rtree/trait.rs
@@ -1,5 +1,6 @@
 use std::cmp::Reverse;
 use std::collections::BinaryHeap;
+use std::marker::PhantomData;
 
 use geo_traits::{CoordTrait, RectTrait};
 
@@ -179,13 +180,13 @@ pub trait RTreeIndex<N: IndexableNum>: Sized {
 
                 if node_index >= self.num_items() as usize * 4 {
                     // node (use even id)
-                    queue.push(Reverse(NeighborNode {
+                    queue.push(Reverse(Neighbor {
                         id: index << 1,
                         dist,
                     }));
                 } else {
                     // leaf item (use odd id)
-                    queue.push(Reverse(NeighborNode {
+                    queue.push(Reverse(Neighbor {
                         id: (index << 1) + 1,
                         dist,
                     }));
@@ -244,21 +245,28 @@ pub trait RTreeIndex<N: IndexableNum>: Sized {
 
 /// A wrapper around a node and its distance for use in the priority queue.
 #[derive(Debug, Clone, Copy, PartialEq)]
-struct NeighborNode<N: IndexableNum> {
+pub struct Neighbor<N: IndexableNum> {
     id: usize,
+    /// Squared distance
     dist: N,
 }
 
-impl<N: IndexableNum> Eq for NeighborNode<N> {}
+impl<N: IndexableNum> Neighbor<N> {
+    pub fn insertion_index(&self) -> u32 {
+        (self.id >> 1).try_into().unwrap()
+    }
+}
+
+impl<N: IndexableNum> Eq for Neighbor<N> {}
 
-impl<N: IndexableNum> Ord for NeighborNode<N> {
+impl<N: IndexableNum> Ord for Neighbor<N> {
     fn cmp(&self, other: &Self) -> std::cmp::Ordering {
         // We don't allow NaN. This should only panic on NaN
         self.dist.partial_cmp(&other.dist).unwrap()
     }
 }
 
-impl<N: IndexableNum> PartialOrd for NeighborNode<N> {
+impl<N: IndexableNum> PartialOrd for Neighbor<N> {
     fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
         Some(self.cmp(other))
     }
@@ -293,7 +301,6 @@ impl<N: IndexableNum> RTreeIndex<N> for RTreeRef<'_, N> {
 }
 
 /// 1D distance from a value to a range.
-#[allow(dead_code)]
 #[inline]
 fn axis_dist<N: IndexableNum>(k: N, min: N, max: N) -> N {
     if k < min {
@@ -305,6 +312,52 @@ fn axis_dist<N: IndexableNum>(k: N, min: N, max: N) -> N {
     }
 }
 
+struct Neighbors<'a, N: IndexableNum> {
+    boxes: &'a [N],
+    indices: Indices<'a>,
+    outer_node_index: Option<usize>,
+    queue: BinaryHeap<Reverse<Neighbor<N>>>,
+}
+
+impl<'a, N: IndexableNum> Neighbors<'a, N> {
+    fn new(boxes: &'a [N], indices: Indices<'a>) -> Self {
+        let outer_node_index = Some(boxes.len() - 4);
+        let queue = BinaryHeap::new();
+        Self {
+            boxes,
+            indices,
+            outer_node_index,
+            queue,
+        }
+    }
+}
+
+impl<N: IndexableNum> Iterator for Neighbors<'_, N> {
+    type Item = Neighbor<N>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        // The queue is not empty and the next item in the queue is a leaf node
+        if !self.queue.is_empty() && self.queue.peek().is_some_and(|val| (val.0.id & 1) != 0) {
+            return Some(self.queue.pop().unwrap().0);
+        };
+
+        if let Some(item) = self.queue.pop() {
+            self.outer_node_index = Some(item.0.id >> 1);
+        } else {
+            return None;
+        }
+
+        // Next: check if outer_node_index is not None
+        // Then: Add child nodes to the queue
+
+        if let Some(node_index) = self.outer_node_index {
+        } else {
+            None
+        }
+        todo!()
+    }
+}
+
 #[cfg(test)]
 mod test {
     // Replication of tests from flatbush js