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//
// Unified Query Algebra
//
// Copyright (c) 2023-2026 Cognica, Inc.
//
//! Cancellable ordered traversal over the dependency's public Thompson states and look assertions.
use std::ops::Range;
use regex_automata::{
nfa::thompson::{State, NFA},
util::primitives::StateID,
};
use uqa_core::memory::{BudgetedVec, MemoryBudget, MemoryError};
use super::{control::Control, states::States, ABSENT};
use crate::AnalysisResult;
#[derive(Clone, Copy)]
enum Pending {
Visit(StateID),
Restore { slot: usize, value: usize },
}
pub(super) struct Cache {
current: States,
next: States,
stack: BudgetedVec<Pending>,
initial: BudgetedVec<usize>,
}
impl Cache {
pub(super) fn new(
nfa: &NFA,
width: usize,
budget: &MemoryBudget,
control: &mut Control<'_>,
) -> AnalysisResult<Self> {
// Every state is expanded at most once per input position. Reserve all possible pending branches and capture restores before traversal.
let mut frames = 1usize;
for state in nfa.states() {
control.step()?;
let additional = match state {
State::Union { alternates } => alternates.len().saturating_sub(1),
State::BinaryUnion { .. } | State::Capture { .. } => 1,
_ => 0,
};
frames = frames
.checked_add(additional)
.ok_or(MemoryError::SizeOverflow)?;
}
let mut stack = BudgetedVec::new(budget);
stack.reserve(frames)?;
Ok(Self {
current: States::new(nfa, width, budget, control)?,
next: States::new(nfa, width, budget, control)?,
stack,
initial: control.buffer(budget, width, ABSENT)?,
})
}
pub(super) fn search(
&mut self,
nfa: &NFA,
text: &str,
span: Range<usize>,
anchored: bool,
result: &mut [usize],
control: &mut Control<'_>,
) -> AnalysisResult<bool> {
self.current.clear();
self.next.clear();
self.stack.clear();
control.fill(&mut self.initial, ABSENT)?;
control.fill(result, ABSENT)?;
let mut matched = false;
let anchored = anchored || nfa.is_always_start_anchored();
for at in span.start..=span.end {
control.step()?;
if self.current.order.is_empty() && (matched || (anchored && at > span.start)) {
break;
}
let closure = Closure {
nfa,
bytes: text.as_bytes(),
at,
};
// Append new start paths after existing paths to preserve leftmost priority. A string regex may only start at a UTF-8 boundary.
if !matched && (!anchored || at == span.start) && text.is_char_boundary(at) {
closure.expand(
nfa.start_anchored(),
&mut self.stack,
&mut self.initial,
&mut self.current,
control,
)?;
}
for index in 0..self.current.order.len() {
control.step()?;
let state = self.current.order[index];
if matches!(nfa.state(state), State::Match { .. }) {
control.copy(self.current.slots(state), result)?;
matched = true;
// Only paths processed before this match can supersede it with a preferred or greedier match.
break;
}
if at == span.end {
continue;
}
let target = match nfa.state(state) {
State::ByteRange { trans } => {
trans.matches(closure.bytes, at).then_some(trans.next)
}
State::Sparse(trans) => trans.matches(closure.bytes, at),
State::Dense(trans) => trans.matches(closure.bytes, at),
_ => None,
};
if let Some(target) = target {
Closure {
at: at + 1,
..closure
}
.expand(
target,
&mut self.stack,
self.current.slots(state),
&mut self.next,
control,
)?;
}
}
std::mem::swap(&mut self.current, &mut self.next);
self.next.clear();
}
Ok(matched)
}
}
#[derive(Clone, Copy)]
struct Closure<'a> {
nfa: &'a NFA,
bytes: &'a [u8],
at: usize,
}
impl Closure<'_> {
fn expand(
&self,
start: StateID,
stack: &mut BudgetedVec<Pending>,
slots: &mut [usize],
target: &mut States,
control: &mut Control<'_>,
) -> AnalysisResult<()> {
stack.push(Pending::Visit(start))?;
while let Some(pending) = stack.pop() {
control.step()?;
match pending {
Pending::Restore { slot, value } => slots[slot] = value,
Pending::Visit(mut state) => loop {
control.step()?;
if !target.insert(state)? {
break;
}
match self.nfa.state(state) {
State::Look { look, next } => {
if !self.nfa.look_matcher().matches(*look, self.bytes, self.at) {
break;
}
state = *next;
}
State::Union { alternates } => {
let Some((&first, rest)) = alternates.split_first() else {
break;
};
for &alternate in rest.iter().rev() {
control.step()?;
stack.push(Pending::Visit(alternate))?;
}
state = first;
}
State::BinaryUnion { alt1, alt2 } => {
stack.push(Pending::Visit(*alt2))?;
state = *alt1;
}
State::Capture { next, slot, .. } => {
let slot = slot.as_usize();
if let Some(value) = slots.get_mut(slot) {
stack.push(Pending::Restore {
slot,
value: *value,
})?;
*value = self.at;
}
state = *next;
}
State::Fail => break,
State::ByteRange { .. }
| State::Sparse(_)
| State::Dense(_)
| State::Match { .. } => {
control.copy(slots, target.slots(state))?;
break;
}
}
},
}
}
Ok(())
}
}