pumpkin_core/propagators/

reified_propagator.rs

use pumpkin_checking::AtomicConstraint;
use pumpkin_checking::BoxedChecker;
use pumpkin_checking::CheckerVariable;
use pumpkin_checking::InferenceChecker;

use crate::engine::PropagationStatusCP;
use crate::engine::notifications::OpaqueDomainEvent;
use crate::predicates::Predicate;
use crate::propagation::DomainEvents;
use crate::propagation::Domains;
use crate::propagation::EnqueueDecision;
use crate::propagation::ExplanationContext;
use crate::propagation::InferenceCheckers;
use crate::propagation::LazyExplanation;
use crate::propagation::LocalId;
use crate::propagation::NotificationContext;
use crate::propagation::Priority;
use crate::propagation::PropagationContext;
use crate::propagation::Propagator;
use crate::propagation::PropagatorConstructor;
use crate::propagation::PropagatorConstructorContext;
use crate::propagation::ReadDomains;
use crate::pumpkin_assert_simple;
use crate::state::Conflict;
use crate::variables::Literal;

/// A [`PropagatorConstructor`] for the reified propagator.
#[derive(Clone, Debug)]
pub struct ReifiedPropagatorArgs<WrappedArgs> {
    pub propagator: WrappedArgs,
    pub reification_literal: Literal,
}

impl<WrappedArgs, WrappedPropagator> PropagatorConstructor for ReifiedPropagatorArgs<WrappedArgs>
where
    WrappedArgs: PropagatorConstructor<PropagatorImpl = WrappedPropagator>,
    WrappedPropagator: Propagator + Clone,
{
    type PropagatorImpl = ReifiedPropagator<WrappedPropagator>;

    fn create(self, mut context: PropagatorConstructorContext) -> Self::PropagatorImpl {
        let ReifiedPropagatorArgs {
            propagator,
            reification_literal,
        } = self;

        let propagator = propagator.create(context.reborrow());
        let reification_literal_id = context.get_next_local_id();

        context.register(
            self.reification_literal,
            DomainEvents::BOUNDS,
            reification_literal_id,
        );

        let name = format!("Reified({})", propagator.name());

        ReifiedPropagator {
            propagator,
            reification_literal,
            reification_literal_id,
            name,
            reason_buffer: vec![],
        }
    }

    fn add_inference_checkers(&self, mut checkers: InferenceCheckers<'_>) {
        checkers.with_reification_literal(self.reification_literal);

        self.propagator.add_inference_checkers(checkers);
    }
}

/// Propagator for the constraint `r -> p`, where `r` is a Boolean literal and `p` is an arbitrary
/// propagator.
///
/// When a propagator is reified, it will only propagate whenever `r` is set to true. However, if
/// the propagator implements [`Propagator::detect_inconsistency`], the result of that method may
/// be used to propagate `r` to false. If that method is not implemented, `r` will never be
/// propagated to false.
#[derive(Clone, Debug)]
pub struct ReifiedPropagator<WrappedPropagator> {
    propagator: WrappedPropagator,
    reification_literal: Literal,
    /// The formatted name of the propagator.
    name: String,
    /// The `LocalId` of the reification literal. Is guaranteed to be a larger ID than any of the
    /// registered ids of the wrapped propagator.
    reification_literal_id: LocalId,

    /// Holds the lazy explanations.
    reason_buffer: Vec<Predicate>,
}

impl<WrappedPropagator: Propagator + Clone> Propagator for ReifiedPropagator<WrappedPropagator> {
    fn notify(
        &mut self,
        mut context: NotificationContext,
        local_id: LocalId,
        event: OpaqueDomainEvent,
    ) -> EnqueueDecision {
        if local_id < self.reification_literal_id {
            let decision = self.propagator.notify(context.reborrow(), local_id, event);
            self.filter_enqueue_decision(context, decision)
        } else {
            pumpkin_assert_simple!(local_id == self.reification_literal_id);
            EnqueueDecision::Enqueue
        }
    }

    fn notify_backtrack(&mut self, context: Domains, local_id: LocalId, event: OpaqueDomainEvent) {
        if local_id < self.reification_literal_id {
            self.propagator.notify_backtrack(context, local_id, event)
        } else {
            pumpkin_assert_simple!(local_id == self.reification_literal_id);
        }
    }

    fn priority(&self) -> Priority {
        self.propagator.priority()
    }

    fn synchronise(&mut self, context: NotificationContext<'_>) {
        self.propagator.synchronise(context);
    }

    fn propagate(&mut self, mut context: PropagationContext) -> PropagationStatusCP {
        self.propagate_reification(&mut context)?;

        if context.evaluate_literal(self.reification_literal) == Some(true) {
            context.with_reification(self.reification_literal);

            let result = self.propagator.propagate(context);

            self.map_propagation_status(result)?;
        }

        Ok(())
    }

    fn name(&self) -> &str {
        &self.name
    }

    fn propagate_from_scratch(&self, mut context: PropagationContext) -> PropagationStatusCP {
        self.propagate_reification(&mut context)?;

        if context.evaluate_literal(self.reification_literal) == Some(true) {
            context.with_reification(self.reification_literal);

            let result = self.propagator.propagate_from_scratch(context);

            self.map_propagation_status(result)?;
        }

        Ok(())
    }

    fn lazy_explanation(&mut self, code: u64, context: ExplanationContext) -> LazyExplanation<'_> {
        let inner = self.propagator.lazy_explanation(code, context);
        let inference_code = inner.inference_code;

        self.reason_buffer.clear();
        self.reason_buffer
            .push(self.reification_literal.get_true_predicate());
        self.reason_buffer.extend(inner.predicates);

        LazyExplanation {
            predicates: self.reason_buffer.as_slice(),
            inference_code,
        }
    }
}

impl<Prop: Propagator + Clone> ReifiedPropagator<Prop> {
    fn map_propagation_status(&self, mut status: PropagationStatusCP) -> PropagationStatusCP {
        if let Err(Conflict::Propagator(ref mut conflict)) = status {
            conflict
                .conjunction
                .push(self.reification_literal.get_true_predicate());
        }
        status
    }

    fn propagate_reification(&self, context: &mut PropagationContext<'_>) -> PropagationStatusCP
    where
        Prop: Propagator,
    {
        if context.evaluate_literal(self.reification_literal) == Some(true) {
            return Ok(());
        }

        if let Some(conflict) = self.propagator.detect_inconsistency(context.domains()) {
            context.post(
                self.reification_literal.get_false_predicate(),
                (conflict.conjunction, &conflict.inference_code),
            )?;
        }

        Ok(())
    }

    fn filter_enqueue_decision(
        &mut self,
        mut context: NotificationContext<'_>,
        decision: EnqueueDecision,
    ) -> EnqueueDecision {
        if decision == EnqueueDecision::Skip {
            // If the original propagator skips then we always skip
            return EnqueueDecision::Skip;
        }

        if context.evaluate_literal(self.reification_literal) == Some(true) {
            // If the propagator would have enqueued and the literal is true then the reified
            // propagator is also enqueued
            return EnqueueDecision::Enqueue;
        }

        if context.evaluate_literal(self.reification_literal) != Some(false)
            && self
                .propagator
                .detect_inconsistency(context.domains())
                .is_some()
        {
            // Or the literal is not false already and there the propagator has found an
            // inconsistency (i.e. we should and can propagate the reification variable)
            return EnqueueDecision::Enqueue;
        }

        EnqueueDecision::Skip
    }
}

#[derive(Debug, Clone)]
pub struct ReifiedChecker<Atomic: AtomicConstraint, Var> {
    pub inner: BoxedChecker<Atomic>,
    pub reification_literal: Var,
}

impl<Atomic: AtomicConstraint + Clone, Var: CheckerVariable<Atomic>> InferenceChecker<Atomic>
    for ReifiedChecker<Atomic, Var>
{
    fn check(
        &self,
        state: pumpkin_checking::VariableState<Atomic>,
        premises: &[Atomic],
        consequent: Option<&Atomic>,
    ) -> bool {
        if self.reification_literal.induced_domain_contains(&state, 0) {
            return false;
        }

        if let Some(consequent) = consequent
            && self
                .reification_literal
                .does_atomic_constrain_self(consequent)
        {
            self.inner.check(state, premises, None)
        } else {
            self.inner.check(state, premises, consequent)
        }
    }
}

#[allow(deprecated, reason = "Will be refactored")]
#[cfg(test)]
mod tests {
    use super::*;
    use crate::conjunction;
    use crate::containers::StorageKey;
    use crate::engine::PropagatorConflict;
    use crate::engine::test_solver::TestSolver;
    use crate::predicate;
    use crate::predicates::PropositionalConjunction;
    use crate::proof::ConstraintTag;
    use crate::proof::InferenceCode;
    use crate::variables::DomainId;

    #[test]
    fn a_detected_inconsistency_is_given_as_reason_for_propagating_reification_literal_to_false() {
        let mut solver = TestSolver::default();

        let reification_literal = solver.new_literal();
        let a = solver.new_variable(1, 1);
        let b = solver.new_variable(2, 2);

        let triggered_conflict = conjunction!([a == 1] & [b == 2]);
        let t1 = triggered_conflict.clone();
        let t2 = triggered_conflict.clone();

        let inference_code = InferenceCode::unknown_label(ConstraintTag::create_from_index(0));
        solver.accept_inferences_by(inference_code.clone());
        let i1 = inference_code.clone();
        let i2 = inference_code.clone();

        let _ = solver
            .new_propagator(ReifiedPropagatorArgs {
                propagator: GenericPropagator::new(
                    move |_: PropagationContext| {
                        Err(PropagatorConflict {
                            conjunction: t1.clone(),
                            inference_code: i1.clone(),
                        }
                        .into())
                    },
                    move |_: Domains| {
                        Some(PropagatorConflict {
                            conjunction: t2.clone(),
                            inference_code: i2.clone(),
                        })
                    },
                ),
                reification_literal,
            })
            .expect("no conflict");

        assert!(solver.is_literal_false(reification_literal));

        let reason = solver.get_reason_bool(reification_literal, false);
        assert_eq!(reason, triggered_conflict);
    }

    #[test]
    fn a_true_literal_is_added_to_reason_for_propagation() {
        let mut solver = TestSolver::default();

        let reification_literal = solver.new_literal();
        let var = solver.new_variable(1, 5);

        let propagator = solver
            .new_propagator(ReifiedPropagatorArgs {
                propagator: GenericPropagator::new(
                    move |mut ctx: PropagationContext| {
                        ctx.post(
                            predicate![var >= 3],
                            (
                                conjunction!(),
                                &InferenceCode::unknown_label(ConstraintTag::create_from_index(0)),
                            ),
                        )?;
                        Ok(())
                    },
                    |_: Domains| None,
                ),
                reification_literal,
            })
            .expect("no conflict");

        solver.assert_bounds(var, 1, 5);

        let _ = solver.set_literal(reification_literal, true);
        solver.propagate(propagator).expect("no conflict");

        solver.assert_bounds(var, 3, 5);
        let reason = solver.get_reason_int(predicate![var >= 3]);
        assert_eq!(
            reason,
            PropositionalConjunction::from(reification_literal.get_true_predicate())
        );
    }

    #[test]
    fn a_true_literal_is_added_to_a_conflict_conjunction() {
        let mut solver = TestSolver::default();

        let reification_literal = solver.new_literal();
        let _ = solver.set_literal(reification_literal, true);

        let var = solver.new_variable(1, 1);
        let inference_code = InferenceCode::unknown_label(ConstraintTag::create_from_index(0));
        solver.accept_inferences_by(inference_code.clone());

        let inconsistency = solver
            .new_propagator(ReifiedPropagatorArgs {
                propagator: GenericPropagator::new(
                    move |_: PropagationContext| {
                        Err(PropagatorConflict {
                            conjunction: conjunction!([var >= 1]),
                            inference_code: inference_code.clone(),
                        }
                        .into())
                    },
                    |_: Domains| None,
                ),
                reification_literal,
            })
            .expect_err("eagerly triggered the conflict");

        match inconsistency {
            Conflict::Propagator(conflict_nogood) => {
                assert_eq!(
                    conflict_nogood.conjunction,
                    PropositionalConjunction::from(vec![
                        reification_literal.get_true_predicate(),
                        predicate![var >= 1]
                    ])
                )
            }

            other => panic!("Inconsistency {other:?} is not expected."),
        }
    }

    #[test]
    fn notify_propagator_is_enqueued_if_inconsistency_can_be_detected() {
        let mut solver = TestSolver::default();

        let reification_literal = solver.new_literal();
        let var = solver.new_variable(1, 5);

        let inference_code = InferenceCode::unknown_label(ConstraintTag::create_from_index(0));
        solver.accept_inferences_by(inference_code.clone());

        let propagator = solver
            .new_propagator(ReifiedPropagatorArgs {
                propagator: GenericPropagator::new(
                    |_: PropagationContext| Ok(()),
                    move |context: Domains| {
                        if context.is_fixed(&var) {
                            Some(PropagatorConflict {
                                conjunction: conjunction!([var == 5]),
                                inference_code: inference_code.clone(),
                            })
                        } else {
                            None
                        }
                    },
                )
                .with_variables(&[var]),
                reification_literal,
            })
            .expect("No conflict expected");

        let enqueue = solver.increase_lower_bound_and_notify(propagator, 0, var, 5);
        assert!(matches!(enqueue, EnqueueDecision::Enqueue))
    }

    #[derive(Clone)]
    struct GenericPropagator<Propagation, ConsistencyCheck> {
        propagation: Propagation,
        consistency_check: ConsistencyCheck,
        variables_to_register: Vec<DomainId>,
    }

    impl<Propagation, ConsistencyCheck> PropagatorConstructor
        for GenericPropagator<Propagation, ConsistencyCheck>
    where
        Propagation: Fn(PropagationContext) -> PropagationStatusCP + 'static + Clone,
        ConsistencyCheck: Fn(Domains) -> Option<PropagatorConflict> + 'static + Clone,
    {
        type PropagatorImpl = Self;

        fn create(self, mut context: PropagatorConstructorContext) -> Self::PropagatorImpl {
            for (index, variable) in self.variables_to_register.iter().enumerate() {
                context.register(
                    *variable,
                    DomainEvents::ANY_INT,
                    LocalId::from(index as u32),
                );
            }

            self
        }
    }

    impl<Propagation, ConsistencyCheck> Propagator for GenericPropagator<Propagation, ConsistencyCheck>
    where
        Propagation: Fn(PropagationContext) -> PropagationStatusCP + 'static + Clone,
        ConsistencyCheck: Fn(Domains) -> Option<PropagatorConflict> + 'static + Clone,
    {
        fn name(&self) -> &str {
            "Generic Propagator"
        }

        fn propagate_from_scratch(&self, context: PropagationContext) -> PropagationStatusCP {
            (self.propagation)(context)
        }

        fn detect_inconsistency(&self, domains: Domains) -> Option<PropagatorConflict> {
            (self.consistency_check)(domains)
        }
    }

    impl<Propagation, ConsistencyCheck> GenericPropagator<Propagation, ConsistencyCheck>
    where
        Propagation: Fn(PropagationContext) -> PropagationStatusCP,
        ConsistencyCheck: Fn(Domains) -> Option<PropagatorConflict>,
    {
        pub(crate) fn new(propagation: Propagation, consistency_check: ConsistencyCheck) -> Self {
            GenericPropagator {
                propagation,
                consistency_check,
                variables_to_register: vec![],
            }
        }

        pub(crate) fn with_variables(mut self, variables: &[DomainId]) -> Self {
            // Necessary for ensuring that the local IDs are correct when notifying
            self.variables_to_register = variables.into();
            self
        }
    }
}