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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 drops the element (vertex, edge, or property) carried by the incoming traverser.
#[derive(Default, Debug)]
pub struct DropStep {
// ── Upstream link ──
upstream: Option<StepRef>,
}
/// Implements the `CoreStep` trait for `DropStep`.
impl CoreStep for DropStep {
/// Wire an upstream step. Called once per upstream during plan construction.
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> {
// Consumes all incoming traversers and drops the elements they carry from the graph context.
let Some(up) = self.upstream.as_deref() else {
return Ok(None);
};
while let Some(el) = up.next(ctx)? {
match &el.value {
GValue::Property(pp) => ctx.drop_property(pp)?,
GValue::Vertex(vt) => ctx.drop_vertex(*vt)?,
GValue::Edge(eg) => ctx.drop_edge(eg)?,
_ => {
return Err(StoreError::UnexpectedDataType("unexpected data type for drop step".into()));
}
}
}
Ok(None)
}
/// Reset all mutable state and propagate to upstreams.
/// 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> {
// Returns a clone of the upstream step reference.
self.upstream.clone()
}
fn explain(&self) -> ExplainNode {
ExplainNode::new("DropStep")
}
}