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// Copyright (c) 2026 Austin Han <austinhan1024@gmail.com>
//
// This file is part of RocksGraph.
//
// RocksGraph is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 2 of the License, or
// (at your option) any later version.
//
// RocksGraph is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with RocksGraph. If not, see <https://www.gnu.org/licenses/>.
use crate::types::PIPELINE_PRODUCE_SIZE;
use std::{collections::VecDeque, rc::Rc};
use smallvec::{smallvec, SmallVec};
use crate::engine::volcano::steps::traits::ExplainNode;
use crate::{
engine::{
context::GraphCtx,
traverser::Traverser,
volcano::steps::traits::{CoreStep, StepRef},
},
types::{error::StoreError, GValue},
};
/// Physical step for `unfold()`: emits each element of a `GValue::List` individually.
/// Non-list values pass through unchanged.
#[derive(Debug)]
pub struct UnfoldStep {
upstream: Option<StepRef>,
/// Whether to link the parent chain on emitted traversers (`false` skips the `Rc::clone`
/// when the plan has no `as()`/`select()`/`path()` anywhere in it).
track_path: bool,
buffer: VecDeque<Rc<Traverser>>,
}
impl UnfoldStep {
pub fn new(track_path: bool) -> Self {
Self { upstream: None, track_path, buffer: VecDeque::new() }
}
}
impl CoreStep for UnfoldStep {
fn add_upper(&mut self, upstream: StepRef) {
self.upstream = Some(upstream);
}
fn produce(
&mut self,
ctx: &mut dyn GraphCtx,
) -> Result<Option<SmallVec<[Rc<Traverser>; PIPELINE_PRODUCE_SIZE]>>, StoreError> {
loop {
if let Some(t) = self.buffer.pop_front() {
return Ok(Some(smallvec![t]));
}
let Some(upstream) = self.upstream.as_ref() else {
return Ok(None);
};
let Some(t) = upstream.next(ctx)? else {
return Ok(None);
};
if let GValue::List(items) = &t.value {
for item in items.iter().rev() {
self.buffer.push_front(Traverser::new_rc_conditional(item.clone(), &t, self.track_path));
}
} else {
return Ok(Some(smallvec![t]));
}
}
}
fn reset(&mut self) {
if let Some(up) = &self.upstream {
up.reset();
}
self.buffer.clear();
}
fn upper(&self) -> Option<StepRef> {
self.upstream.clone()
}
fn explain(&self) -> ExplainNode {
ExplainNode::new("UnfoldStep")
}
}