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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, SmallVec};
use crate::engine::volcano::steps::traits::ExplainNode;
use crate::{
engine::{
context::GraphCtx,
traverser::Traverser,
volcano::steps::traits::{CoreStep, StepRef},
},
types::{
error::StoreError,
gvalue::{GValue, Primitive},
},
};
/// A physical step that counts the number of traversers received from its upstream.
#[derive(Default, Debug)]
pub struct CountStep {
// ── Upstream link ──
upstream: Option<StepRef>,
// ── Dynamic/Runtime execution state ──
/// Whether the count has already been produced.
done: bool,
}
/// Implements the `CoreStep` trait for `CountStep`.
impl CoreStep for CountStep {
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> {
if self.done {
// Only produces a single count result.
return Ok(None);
}
let Some(upstream) = self.upstream.as_ref() else { return Ok(None) };
let mut count: i64 = 0;
while upstream.next(ctx)?.is_some() {
count += 1;
}
self.done = true;
Ok(Some(smallvec![Traverser::new_rc(GValue::Scalar(Primitive::Int64(count)))]))
}
fn reset(&mut self) {
// Resets the step's internal state, allowing it to recount.
self.done = false;
if let Some(up) = &self.upstream {
up.reset();
}
}
/// Returns a clone of the upstream step reference.
fn upper(&self) -> Option<StepRef> {
self.upstream.clone()
}
fn explain(&self) -> ExplainNode {
ExplainNode::new("CountStep")
}
}