solverforge_solver/heuristic/move/

list_swap.rs

/* ListSwapMove - swaps two elements within or between list variables.

This move exchanges two elements at different positions.
Useful for TSP-style improvements and route optimization.

# Zero-Erasure Design

Uses concrete function pointers for list operations. No `dyn Any`, no downcasting.
*/

use std::fmt::Debug;

use smallvec::{smallvec, SmallVec};
use solverforge_core::domain::PlanningSolution;
use solverforge_scoring::Director;

use super::metadata::{
    encode_option_debug, encode_usize, ordered_coordinate_pair, scoped_move_identity,
    MoveTabuScope, ScopedEntityTabuToken, TABU_OP_LIST_SWAP,
};
use super::{Move, MoveTabuSignature};

/// A move that swaps two elements in list variables.
///
/// Supports both intra-list swaps (within same entity) and inter-list swaps
/// (between different entities). Uses concrete function pointers for zero-erasure.
///
/// # Type Parameters
/// * `S` - The planning solution type
/// * `V` - The list element value type
///
/// # Example
///
/// ```
/// use solverforge_solver::heuristic::r#move::ListSwapMove;
/// use solverforge_core::domain::PlanningSolution;
/// use solverforge_core::score::SoftScore;
///
/// #[derive(Clone, Debug)]
/// struct Vehicle { id: usize, visits: Vec<i32> }
///
/// #[derive(Clone, Debug)]
/// struct Solution { vehicles: Vec<Vehicle>, score: Option<SoftScore> }
///
/// impl PlanningSolution for Solution {
///     type Score = SoftScore;
///     fn score(&self) -> Option<Self::Score> { self.score }
///     fn set_score(&mut self, score: Option<Self::Score>) { self.score = score; }
/// }
///
/// fn list_len(s: &Solution, entity_idx: usize) -> usize {
///     s.vehicles.get(entity_idx).map_or(0, |v| v.visits.len())
/// }
/// fn list_get(s: &Solution, entity_idx: usize, pos: usize) -> Option<i32> {
///     s.vehicles.get(entity_idx).and_then(|v| v.visits.get(pos).copied())
/// }
/// fn list_set(s: &mut Solution, entity_idx: usize, pos: usize, val: i32) {
///     if let Some(v) = s.vehicles.get_mut(entity_idx) {
///         if let Some(elem) = v.visits.get_mut(pos) { *elem = val; }
///     }
/// }
///
/// // Swap elements at positions 1 and 3 in vehicle 0
/// let m = ListSwapMove::<Solution, i32>::new(
///     0, 1, 0, 3,
///     list_len, list_get, list_set,
///     "visits", 0,
/// );
/// ```
pub struct ListSwapMove<S, V> {
    // First entity index
    first_entity_index: usize,
    // Position in first entity's list
    first_position: usize,
    // Second entity index
    second_entity_index: usize,
    // Position in second entity's list
    second_position: usize,
    list_len: fn(&S, usize) -> usize,
    list_get: fn(&S, usize, usize) -> Option<V>,
    // Set element at position
    list_set: fn(&mut S, usize, usize, V),
    variable_name: &'static str,
    descriptor_index: usize,
    // Store indices for entity_indices()
    indices: [usize; 2],
}

impl<S, V> Clone for ListSwapMove<S, V> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<S, V> Copy for ListSwapMove<S, V> {}

impl<S, V: Debug> Debug for ListSwapMove<S, V> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("ListSwapMove")
            .field("first_entity", &self.first_entity_index)
            .field("first_position", &self.first_position)
            .field("second_entity", &self.second_entity_index)
            .field("second_position", &self.second_position)
            .field("variable_name", &self.variable_name)
            .finish()
    }
}

impl<S, V> ListSwapMove<S, V> {
    /* Creates a new list swap move with concrete function pointers.

    # Arguments
    * `first_entity_index` - First entity index
    * `first_position` - Position in first entity's list
    * `second_entity_index` - Second entity index
    * `second_position` - Position in second entity's list
    * `list_len` - Function to get list length
    * `list_get` - Function to get element at position
    * `list_set` - Function to set element at position
    * `variable_name` - Name of the list variable
    * `descriptor_index` - Entity descriptor index
    */
    #[allow(clippy::too_many_arguments)]
    pub fn new(
        first_entity_index: usize,
        first_position: usize,
        second_entity_index: usize,
        second_position: usize,
        list_len: fn(&S, usize) -> usize,
        list_get: fn(&S, usize, usize) -> Option<V>,
        list_set: fn(&mut S, usize, usize, V),
        variable_name: &'static str,
        descriptor_index: usize,
    ) -> Self {
        Self {
            first_entity_index,
            first_position,
            second_entity_index,
            second_position,
            list_len,
            list_get,
            list_set,
            variable_name,
            descriptor_index,
            indices: [first_entity_index, second_entity_index],
        }
    }

    pub fn first_entity_index(&self) -> usize {
        self.first_entity_index
    }

    pub fn first_position(&self) -> usize {
        self.first_position
    }

    pub fn second_entity_index(&self) -> usize {
        self.second_entity_index
    }

    pub fn second_position(&self) -> usize {
        self.second_position
    }

    pub fn is_intra_list(&self) -> bool {
        self.first_entity_index == self.second_entity_index
    }
}

impl<S, V> Move<S> for ListSwapMove<S, V>
where
    S: PlanningSolution,
    V: Clone + PartialEq + Send + Sync + Debug + 'static,
{
    type Undo = ();

    fn is_doable<D: Director<S>>(&self, score_director: &D) -> bool {
        let solution = score_director.working_solution();

        // Check first position is valid
        let first_len = (self.list_len)(solution, self.first_entity_index);
        if self.first_position >= first_len {
            return false;
        }

        // Check second position is valid
        let second_len = (self.list_len)(solution, self.second_entity_index);
        if self.second_position >= second_len {
            return false;
        }

        // For intra-list, can't swap with self
        if self.is_intra_list() && self.first_position == self.second_position {
            return false;
        }

        // Get values and check they're different
        let first_val = (self.list_get)(solution, self.first_entity_index, self.first_position);
        let second_val = (self.list_get)(solution, self.second_entity_index, self.second_position);

        first_val != second_val
    }

    fn do_move<D: Director<S>>(&self, score_director: &mut D) -> Self::Undo {
        // Get both values
        let first_val = (self.list_get)(
            score_director.working_solution(),
            self.first_entity_index,
            self.first_position,
        )
        .expect("first position should be valid");

        let second_val = (self.list_get)(
            score_director.working_solution(),
            self.second_entity_index,
            self.second_position,
        )
        .expect("second position should be valid");

        // Notify before changes
        score_director.before_variable_changed(self.descriptor_index, self.first_entity_index);
        if !self.is_intra_list() {
            score_director.before_variable_changed(self.descriptor_index, self.second_entity_index);
        }

        // Swap: first gets second's value, second gets first's value
        (self.list_set)(
            score_director.working_solution_mut(),
            self.first_entity_index,
            self.first_position,
            second_val.clone(),
        );
        (self.list_set)(
            score_director.working_solution_mut(),
            self.second_entity_index,
            self.second_position,
            first_val.clone(),
        );

        // Notify after changes
        score_director.after_variable_changed(self.descriptor_index, self.first_entity_index);
        if !self.is_intra_list() {
            score_director.after_variable_changed(self.descriptor_index, self.second_entity_index);
        }
    }

    fn undo_move<D: Director<S>>(&self, score_director: &mut D, (): Self::Undo) {
        self.do_move(score_director);
    }

    fn descriptor_index(&self) -> usize {
        self.descriptor_index
    }

    fn entity_indices(&self) -> &[usize] {
        if self.is_intra_list() {
            &self.indices[0..1]
        } else {
            &self.indices
        }
    }

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

    fn tabu_signature<D: Director<S>>(&self, score_director: &D) -> MoveTabuSignature {
        let first_val = (self.list_get)(
            score_director.working_solution(),
            self.first_entity_index,
            self.first_position,
        );
        let second_val = (self.list_get)(
            score_director.working_solution(),
            self.second_entity_index,
            self.second_position,
        );
        let first_id = encode_option_debug(first_val.as_ref());
        let second_id = encode_option_debug(second_val.as_ref());
        let first_entity_id = encode_usize(self.first_entity_index);
        let second_entity_id = encode_usize(self.second_entity_index);
        let scope = MoveTabuScope::new(self.descriptor_index, self.variable_name);
        let mut entity_tokens: SmallVec<[ScopedEntityTabuToken; 2]> =
            smallvec![scope.entity_token(first_entity_id)];
        if !self.is_intra_list() {
            entity_tokens.push(scope.entity_token(second_entity_id));
        }
        let coordinate_pair = ordered_coordinate_pair(
            (first_entity_id, encode_usize(self.first_position)),
            (second_entity_id, encode_usize(self.second_position)),
        );
        let move_id = scoped_move_identity(
            scope,
            TABU_OP_LIST_SWAP,
            coordinate_pair
                .into_iter()
                .flat_map(|(entity_id, position)| [entity_id, position]),
        );

        MoveTabuSignature::new(scope, move_id.clone(), move_id)
            .with_entity_tokens(entity_tokens)
            .with_destination_value_tokens([
                scope.value_token(second_id),
                scope.value_token(first_id),
            ])
    }
}