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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, SMALL_VECTOR_LENGTH};
use std::rc::Rc;
use smallvec::{smallvec, SmallVec};
use crate::engine::volcano::steps::traits::ExplainNode;
use crate::{
engine::{
context::GraphCtx,
traverser::Traverser,
volcano::{
builder::PhysicalPlan,
steps::traits::{CoreStep, StepRef},
},
},
types::error::StoreError,
};
/// A physical step that implements the `union` logical step.
#[derive(Debug)]
pub struct UnionStep {
// ── Upstream link ──
upstream: Option<StepRef>,
// ── Static/Fixed configuration ──
/// The physical plans representing the branches of the union.
physical_plans: SmallVec<[PhysicalPlan; SMALL_VECTOR_LENGTH]>,
// ── Dynamic/Runtime execution state ──
/// The index of the current branch plan being evaluated for the active input.
current_plan_idx: usize,
/// The parent traverser currently being processed.
current_input: Option<Rc<Traverser>>,
}
impl UnionStep {
/// Creates a new `UnionStep` with the given physical sub-plans.
pub fn new(physical_plans: SmallVec<[PhysicalPlan; SMALL_VECTOR_LENGTH]>) -> Self {
Self { upstream: None, physical_plans, current_plan_idx: 0, current_input: None }
}
}
impl CoreStep for UnionStep {
fn add_upper(&mut self, upstream: StepRef) {
// Sets the upstream step for this union step.
self.upstream = Some(upstream);
}
fn produce(
&mut self,
ctx: &mut dyn GraphCtx,
) -> Result<Option<SmallVec<[Rc<Traverser>; PIPELINE_PRODUCE_SIZE]>>, StoreError> {
// Continuously attempts to produce traversers from its sub-plans.
loop {
if self.current_input.is_none() {
let Some(upstream) = self.upstream.as_ref() else { return Ok(None) };
let Some(t) = upstream.next(ctx)? else { return Ok(None) };
self.current_input = Some(Rc::clone(&t));
self.current_plan_idx = 0;
if !self.physical_plans.is_empty() {
let p = &self.physical_plans[0];
p.reset();
p.inject(smallvec![Rc::clone(&t)]);
}
}
if self.physical_plans.is_empty() {
self.current_input = None;
continue;
}
let p = &self.physical_plans[self.current_plan_idx];
if let Some(res) = p.next(ctx)? {
return Ok(Some(smallvec![res]));
}
self.current_plan_idx += 1;
if self.current_plan_idx < self.physical_plans.len() {
let next_p = &self.physical_plans[self.current_plan_idx];
next_p.reset();
next_p.inject(smallvec![Rc::clone(self.current_input.as_ref().unwrap())]);
} else {
self.current_input = None;
}
}
}
fn reset(&mut self) {
// Resets the state of this step and all its upstream and sub-plans.
if let Some(up) = &self.upstream {
up.reset();
}
for p in &self.physical_plans {
p.reset();
}
self.current_input = None;
self.current_plan_idx = 0;
}
fn upper(&self) -> Option<StepRef> {
// Returns a clone of the upstream step reference.
self.upstream.clone()
}
fn explain(&self) -> ExplainNode {
let children =
self.physical_plans.iter().enumerate().map(|(i, plan)| (format!("branch {}", i), plan.explain())).collect();
ExplainNode::new("UnionStep").with_children(children)
}
}