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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::rc::Rc;
use 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},
};
/// A physical step that extracts the "other" vertex from an edge traverser.
#[derive(Debug)]
pub struct OtherVStep {
// ── Upstream link ──
upstream: Option<StepRef>,
// ── Static/Fixed configuration ──
/// 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,
}
impl OtherVStep {
pub fn new(track_path: bool) -> Self {
Self { upstream: None, track_path }
}
}
/// Implements the `CoreStep` trait for `OtherVStep`.
impl CoreStep for OtherVStep {
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> {
let Some(upstream) = self.upstream.as_ref() else { return Ok(None) };
let mut batch = SmallVec::with_capacity(PIPELINE_PRODUCE_SIZE);
while batch.len() < PIPELINE_PRODUCE_SIZE {
let Some(t) = upstream.next(ctx)? else { break };
match &t.value {
GValue::Edge(ek) => {
batch.push(Traverser::new_rc_conditional(GValue::Vertex(ek.secondary_id), &t, self.track_path))
}
other => {
return Err(StoreError::UnexpectedDataType(format!("otherV() expects an Edge, got {:?}", other)))
}
}
}
if batch.is_empty() {
Ok(None)
} else {
Ok(Some(batch))
}
}
/// Resets the state of this step and its upstream.
fn reset(&mut self) {
if let Some(up) = &self.upstream {
up.reset();
}
}
fn upper(&self) -> Option<StepRef> {
self.upstream.clone()
}
fn explain(&self) -> ExplainNode {
ExplainNode::new("OtherVStep")
}
}