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//! Forward iterator over entries in a persistent B+ tree.
//!
//! Uses an explicit ancestor stack — no sibling pointers needed.
use std::ops::Bound;
use super::{EMPTY_ROOT, LeafState, Node, NodeId, PersistentBTree};
/// A forward iterator over entries in a [`PersistentBTree`].
///
/// Uses an explicit ancestor stack — no sibling pointers needed.
pub struct BTreeIter<'a> {
tree: &'a PersistentBTree,
stack: Vec<(Node, usize)>,
leaf: Option<LeafState>,
hi: Bound<Vec<u8>>,
done: bool,
}
impl<'a> BTreeIter<'a> {
pub(crate) fn new(
tree: &'a PersistentBTree,
root: NodeId,
lo: Bound<Vec<u8>>,
hi: Bound<Vec<u8>>,
) -> Self {
let mut it = Self {
tree,
stack: Vec::with_capacity(8),
leaf: None,
hi,
done: root == EMPTY_ROOT,
};
if !it.done {
it.seek(root, &lo);
}
it
}
fn seek(&mut self, id: NodeId, lo: &Bound<Vec<u8>>) {
let mut cur = id;
loop {
let node = self.tree.node(cur);
match &node {
Node::Internal { keys, children } => {
let ci = match lo {
Bound::Unbounded => 0,
Bound::Included(k) | Bound::Excluded(k) => {
match keys.binary_search_by(|x| x.as_slice().cmp(k)) {
Ok(i) => i + 1,
Err(i) => i,
}
}
};
let child = children[ci];
self.stack.push((node, ci + 1));
cur = child;
}
Node::Leaf { keys, values } => {
let start = match lo {
Bound::Unbounded => 0,
Bound::Included(k) => keys
.binary_search_by(|x| x.as_slice().cmp(k))
.unwrap_or_else(|i| i),
Bound::Excluded(k) => {
match keys.binary_search_by(|x| x.as_slice().cmp(k)) {
Ok(i) => i + 1,
Err(i) => i,
}
}
};
if start < keys.len() {
self.leaf = Some((keys.clone(), values.clone(), start));
} else {
self.advance_leaf();
}
return;
}
}
}
}
fn advance_leaf(&mut self) {
self.leaf = None;
while let Some((node, next_ci)) = self.stack.last_mut() {
if let Node::Internal { children, .. } = node
&& *next_ci < children.len()
{
let child_id = children[*next_ci];
*next_ci += 1;
self.descend_leftmost(child_id);
return;
}
self.stack.pop();
}
self.done = true;
}
fn descend_leftmost(&mut self, id: NodeId) {
let mut cur = id;
loop {
let node = self.tree.node(cur);
match &node {
Node::Internal { children, .. } => {
let child = children[0];
self.stack.push((node, 1));
cur = child;
}
Node::Leaf { keys, values } => {
if keys.is_empty() {
self.advance_leaf();
} else {
self.leaf = Some((keys.clone(), values.clone(), 0));
}
return;
}
}
}
}
}
impl Iterator for BTreeIter<'_> {
type Item = (Vec<u8>, Vec<u8>);
fn next(&mut self) -> Option<Self::Item> {
loop {
if self.done {
return None;
}
if let Some((ref keys, ref values, ref mut pos)) = self.leaf {
if *pos < keys.len() {
let key = &keys[*pos];
let within = match &self.hi {
Bound::Unbounded => true,
Bound::Included(h) => key.as_slice() <= h.as_slice(),
Bound::Excluded(h) => key.as_slice() < h.as_slice(),
};
if !within {
self.done = true;
return None;
}
let kv = (key.clone(), values[*pos].clone());
*pos += 1;
return Some(kv);
}
} else {
self.done = true;
return None;
}
// Leaf exhausted — advance.
self.advance_leaf();
}
}
}