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use anyhow::Result;
use std::ops::Deref;
use crate::fst_properties::FstProperties;
use crate::fst_traits::MutableFst;
use crate::semirings::Semiring;
use crate::Tr;
use crate::{Label, StateId, EPS_LABEL};
/// Struct used to map final weights when performing a transition mapping.
/// It will always be of the form `(EPS_LABEL, EPS_LABEL, final_weight)`
/// where `final_weight` is the `final_weight` of the current state.
///
/// If the mapper modifies the input label or output one,
/// a super final state will need to be created.
#[derive(Clone, Debug)]
pub struct FinalTr<W: Semiring> {
/// Input label. Default to `EPS_LABEL`.
pub ilabel: Label,
/// Output label. Default to `EPS_LABEL`.
pub olabel: Label,
/// Weight. Default to the final weight of the current state.
pub weight: W,
}
/// Determines how final weights are mapped.
#[derive(PartialEq)]
pub enum MapFinalAction {
/// A final weight is mapped into a final weight. An error is raised if this
/// is not possible.
MapNoSuperfinal,
/// A final weight is mapped to a transition to the superfinal state when the result
/// cannot be represented as a final weight. The superfinal state will be
/// added only if it is needed.
MapAllowSuperfinal,
/// A final weight is mapped to a transition to the superfinal state unless the
/// result can be represented as a final weight of weight Zero(). The
/// superfinal state is always added (if the input is not the empty FST).
MapRequireSuperfinal,
}
/// The TrMapper interfaces defines how trs and final weights are mapped.
/// This is useful for implementing operations that do not change the number of
/// trs.
pub trait TrMapper<S: Semiring> {
/// How to modify the trs.
fn tr_map(&self, tr: &mut Tr<S>) -> Result<()>;
/// The mapper will be passed final weights as trs of the form
/// `FinalTr(EPS_LABEL, EPS_LABEL, weight)`.
fn final_tr_map(&self, final_tr: &mut FinalTr<S>) -> Result<()>;
/// Specifies final action the mapper requires (see above).
fn final_action(&self) -> MapFinalAction;
fn properties(&self, inprops: FstProperties) -> FstProperties;
}
impl<S: Semiring, T: TrMapper<S>, TP: Deref<Target = T>> TrMapper<S> for TP {
fn tr_map(&self, tr: &mut Tr<S>) -> Result<()> {
self.deref().tr_map(tr)
}
fn final_tr_map(&self, final_tr: &mut FinalTr<S>) -> Result<()> {
self.deref().final_tr_map(final_tr)
}
fn final_action(&self) -> MapFinalAction {
self.deref().final_action()
}
fn properties(&self, inprops: FstProperties) -> FstProperties {
self.deref().properties(inprops)
}
}
/// Maps every transition in the FST using an `TrMapper` object.
pub fn tr_map<W, F, M>(ifst: &mut F, mapper: &M) -> Result<()>
where
W: Semiring,
F: MutableFst<W>,
M: TrMapper<W>,
{
if ifst.start().is_none() {
return Ok(());
}
let inprops = ifst.properties();
let final_action = mapper.final_action();
let mut superfinal: Option<StateId> = None;
if final_action == MapFinalAction::MapRequireSuperfinal {
let superfinal_id = ifst.add_state();
superfinal = Some(superfinal_id);
ifst.set_final(superfinal_id, W::one()).unwrap();
}
for state in 0..(ifst.num_states() as StateId) {
unsafe {
let mut it_tr = ifst.tr_iter_unchecked_mut(state);
for idx_tr in 0..it_tr.len() {
let mut tr = it_tr.get_unchecked(idx_tr).clone();
mapper.tr_map(&mut tr)?;
it_tr.set_tr_unchecked(idx_tr, tr);
}
}
if let Some(w) = unsafe { ifst.final_weight_unchecked(state) } {
let mut final_tr = FinalTr {
ilabel: EPS_LABEL,
olabel: EPS_LABEL,
weight: w,
};
mapper.final_tr_map(&mut final_tr)?;
match final_action {
MapFinalAction::MapNoSuperfinal => {
if final_tr.ilabel != EPS_LABEL || final_tr.olabel != EPS_LABEL {
bail!("TrMap: Non-zero tr labels for superfinal tr")
}
unsafe {
ifst.set_final_unchecked(state, final_tr.weight);
}
}
MapFinalAction::MapAllowSuperfinal => {
if Some(state) != superfinal {
if final_tr.ilabel != EPS_LABEL || final_tr.olabel != EPS_LABEL {
if superfinal.is_none() {
let superfinal_id = ifst.add_state();
superfinal = Some(superfinal_id);
unsafe {
// Checked because the state is created just above
ifst.set_final_unchecked(superfinal_id, W::one());
}
}
unsafe {
// Checked
ifst.add_tr_unchecked(
state,
Tr::new(
final_tr.ilabel,
final_tr.olabel,
final_tr.weight,
superfinal.unwrap(), // Checked
),
);
ifst.delete_final_weight_unchecked(state);
}
} else {
unsafe {
// Checked
ifst.set_final_unchecked(state, final_tr.weight);
}
}
}
}
MapFinalAction::MapRequireSuperfinal => {
if Some(state) != superfinal
&& (final_tr.ilabel != EPS_LABEL
|| final_tr.olabel != EPS_LABEL
|| !final_tr.weight.is_zero())
{
unsafe {
// checked
ifst.add_tr_unchecked(
state,
Tr::new(
final_tr.ilabel,
final_tr.olabel,
final_tr.weight,
superfinal.unwrap(),
),
);
ifst.delete_final_weight_unchecked(state);
}
}
}
};
}
}
ifst.set_properties_with_mask(mapper.properties(inprops), FstProperties::all_properties());
Ok(())
}