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use super::{Byte, Ref, Tree, Uninhabited};
use crate::{Map, Set};
use std::fmt;
use std::sync::atomic::{AtomicU32, Ordering};
#[derive(PartialEq, Debug)]
pub(crate) struct Nfa<R>
where
R: Ref,
{
pub(crate) transitions: Map<State, Map<Transition<R>, Set<State>>>,
pub(crate) start: State,
pub(crate) accepting: State,
}
#[derive(Hash, Eq, PartialEq, PartialOrd, Ord, Copy, Clone)]
pub(crate) struct State(u32);
#[derive(Hash, Eq, PartialEq, Clone, Copy)]
pub(crate) enum Transition<R>
where
R: Ref,
{
Byte(Byte),
Ref(R),
}
impl fmt::Debug for State {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "S_{}", self.0)
}
}
impl<R> fmt::Debug for Transition<R>
where
R: Ref,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match &self {
Self::Byte(b) => b.fmt(f),
Self::Ref(r) => r.fmt(f),
}
}
}
impl<R> Nfa<R>
where
R: Ref,
{
pub(crate) fn unit() -> Self {
let transitions: Map<State, Map<Transition<R>, Set<State>>> = Map::default();
let start = State::new();
let accepting = start;
Nfa { transitions, start, accepting }
}
pub(crate) fn from_byte(byte: Byte) -> Self {
let mut transitions: Map<State, Map<Transition<R>, Set<State>>> = Map::default();
let start = State::new();
let accepting = State::new();
let source = transitions.entry(start).or_default();
let edge = source.entry(Transition::Byte(byte)).or_default();
edge.insert(accepting);
Nfa { transitions, start, accepting }
}
pub(crate) fn from_ref(r: R) -> Self {
let mut transitions: Map<State, Map<Transition<R>, Set<State>>> = Map::default();
let start = State::new();
let accepting = State::new();
let source = transitions.entry(start).or_default();
let edge = source.entry(Transition::Ref(r)).or_default();
edge.insert(accepting);
Nfa { transitions, start, accepting }
}
pub(crate) fn from_tree(tree: Tree<!, R>) -> Result<Self, Uninhabited> {
Ok(match tree {
Tree::Byte(b) => Self::from_byte(b),
Tree::Def(..) => unreachable!(),
Tree::Ref(r) => Self::from_ref(r),
Tree::Alt(alts) => {
let mut alts = alts.into_iter().map(Self::from_tree);
let mut nfa = alts.next().ok_or(Uninhabited)??;
for alt in alts {
nfa = nfa.union(alt?);
}
nfa
}
Tree::Seq(elts) => {
let mut nfa = Self::unit();
for elt in elts.into_iter().map(Self::from_tree) {
nfa = nfa.concat(elt?);
}
nfa
}
})
}
pub(crate) fn concat(self, other: Self) -> Self {
if self.start == self.accepting {
return other;
} else if other.start == other.accepting {
return self;
}
let start = self.start;
let accepting = other.accepting;
let mut transitions: Map<State, Map<Transition<R>, Set<State>>> = self.transitions;
for (source, transition) in other.transitions {
let fix_state = |state| if state == other.start { self.accepting } else { state };
let entry = transitions.entry(fix_state(source)).or_default();
for (edge, destinations) in transition {
let entry = entry.entry(edge.clone()).or_default();
for destination in destinations {
entry.insert(fix_state(destination));
}
}
}
Self { transitions, start, accepting }
}
pub(crate) fn union(self, other: Self) -> Self {
let start = self.start;
let accepting = self.accepting;
let mut transitions: Map<State, Map<Transition<R>, Set<State>>> = self.transitions.clone();
for (&(mut source), transition) in other.transitions.iter() {
if source == other.start {
source = self.start;
}
let entry = transitions.entry(source).or_default();
for (edge, destinations) in transition {
let entry = entry.entry(edge.clone()).or_default();
for &(mut destination) in destinations {
if destination == other.accepting {
destination = self.accepting;
}
entry.insert(destination);
}
}
}
Self { transitions, start, accepting }
}
pub(crate) fn edges_from(&self, start: State) -> Option<&Map<Transition<R>, Set<State>>> {
self.transitions.get(&start)
}
}
impl State {
pub(crate) fn new() -> Self {
static COUNTER: AtomicU32 = AtomicU32::new(0);
Self(COUNTER.fetch_add(1, Ordering::SeqCst))
}
}