solverforge_solver/heuristic/selector/

list_change.rs

/* List change move selector for element relocation.

Generates `ListChangeMove`s that relocate elements within or between list variables.
Essential for vehicle routing and scheduling problems.

# Example

```
use solverforge_solver::heuristic::selector::list_change::ListChangeMoveSelector;
use solverforge_solver::heuristic::selector::entity::FromSolutionEntitySelector;
use solverforge_solver::heuristic::selector::MoveSelector;
use solverforge_core::domain::PlanningSolution;
use solverforge_core::score::SoftScore;

#[derive(Clone, Debug)]
struct Vehicle { 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_remove(s: &mut Solution, entity_idx: usize, pos: usize) -> Option<i32> {
s.vehicles.get_mut(entity_idx).map(|v| v.visits.remove(pos))
}
fn list_insert(s: &mut Solution, entity_idx: usize, pos: usize, val: i32) {
if let Some(v) = s.vehicles.get_mut(entity_idx) { v.visits.insert(pos, val); }
}

let selector = ListChangeMoveSelector::<Solution, i32, _>::new(
FromSolutionEntitySelector::new(0),
list_len,
list_remove,
list_insert,
"visits",
0,
);
```
*/

use std::fmt::Debug;
use std::marker::PhantomData;

use solverforge_core::domain::PlanningSolution;
use solverforge_scoring::Director;

use crate::heuristic::r#move::ListChangeMove;

use super::entity::EntitySelector;
use super::typed_move_selector::MoveSelector;

/// A move selector that generates list change moves.
///
/// Enumerates all valid (source_entity, source_pos, dest_entity, dest_pos)
/// combinations for relocating elements within or between list variables.
///
/// # Type Parameters
/// * `S` - The solution type
/// * `V` - The list element type
///
/// # Complexity
///
/// For n entities with average route length m:
/// - Intra-entity moves: O(n * m * m)
/// - Inter-entity moves: O(n * n * m * m)
/// - Total: O(n² * m²) worst case
///
/// Use with a forager that quits early for better performance.
pub struct ListChangeMoveSelector<S, V, ES> {
    // Selects entities (vehicles) for moves.
    entity_selector: ES,
    list_len: fn(&S, usize) -> usize,
    // Remove element at position.
    list_remove: fn(&mut S, usize, usize) -> Option<V>,
    // Insert element at position.
    list_insert: fn(&mut S, usize, usize, V),
    // Variable name for notifications.
    variable_name: &'static str,
    // Entity descriptor index.
    descriptor_index: usize,
    _phantom: PhantomData<(fn() -> S, fn() -> V)>,
}

impl<S, V: Debug, ES: Debug> Debug for ListChangeMoveSelector<S, V, ES> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("ListChangeMoveSelector")
            .field("entity_selector", &self.entity_selector)
            .field("variable_name", &self.variable_name)
            .field("descriptor_index", &self.descriptor_index)
            .finish()
    }
}

impl<S, V, ES> ListChangeMoveSelector<S, V, ES> {
    /// Creates a new list change move selector.
    ///
    /// # Arguments
    /// * `entity_selector` - Selects entities to consider for moves
    /// * `list_len` - Function to get list length for an entity
    /// * `list_remove` - Function to remove element at position
    /// * `list_insert` - Function to insert element at position
    /// * `variable_name` - Name of the list variable
    /// * `descriptor_index` - Entity descriptor index
    pub fn new(
        entity_selector: ES,
        list_len: fn(&S, usize) -> usize,
        list_remove: fn(&mut S, usize, usize) -> Option<V>,
        list_insert: fn(&mut S, usize, usize, V),
        variable_name: &'static str,
        descriptor_index: usize,
    ) -> Self {
        Self {
            entity_selector,
            list_len,
            list_remove,
            list_insert,
            variable_name,
            descriptor_index,
            _phantom: PhantomData,
        }
    }
}

impl<S, V, ES> MoveSelector<S, ListChangeMove<S, V>> for ListChangeMoveSelector<S, V, ES>
where
    S: PlanningSolution,
    V: Clone + PartialEq + Send + Sync + Debug + 'static,
    ES: EntitySelector<S>,
{
    fn iter_moves<'a, D: Director<S>>(
        &'a self,
        score_director: &'a D,
    ) -> impl Iterator<Item = ListChangeMove<S, V>> + 'a {
        let solution = score_director.working_solution();
        let list_len = self.list_len;
        let list_remove = self.list_remove;
        let list_insert = self.list_insert;
        let variable_name = self.variable_name;
        let descriptor_index = self.descriptor_index;

        // Collect entities to allow multiple passes
        let entities: Vec<usize> = self
            .entity_selector
            .iter(score_director)
            .map(|r| r.entity_index)
            .collect();

        // Pre-compute route lengths
        let route_lens: Vec<usize> = entities.iter().map(|&e| list_len(solution, e)).collect();

        // Generate all valid moves
        let mut moves = Vec::new();

        for (src_idx, &src_entity) in entities.iter().enumerate() {
            let src_len = route_lens[src_idx];
            if src_len == 0 {
                continue;
            }

            for src_pos in 0..src_len {
                // Intra-entity moves
                for dst_pos in 0..src_len {
                    /* Skip no-op moves:
                    - Same position is obviously a no-op
                    - Forward by 1 is a no-op due to index adjustment during do_move
                    */
                    if src_pos == dst_pos || dst_pos == src_pos + 1 {
                        continue;
                    }

                    moves.push(ListChangeMove::new(
                        src_entity,
                        src_pos,
                        src_entity,
                        dst_pos,
                        list_len,
                        list_remove,
                        list_insert,
                        variable_name,
                        descriptor_index,
                    ));
                }

                // Inter-entity moves
                for (dst_idx, &dst_entity) in entities.iter().enumerate() {
                    if dst_idx == src_idx {
                        continue;
                    }

                    let dst_len = route_lens[dst_idx];
                    // Can insert at any position from 0 to dst_len inclusive
                    for dst_pos in 0..=dst_len {
                        moves.push(ListChangeMove::new(
                            src_entity,
                            src_pos,
                            dst_entity,
                            dst_pos,
                            list_len,
                            list_remove,
                            list_insert,
                            variable_name,
                            descriptor_index,
                        ));
                    }
                }
            }
        }

        moves.into_iter()
    }

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

        let entities: Vec<usize> = self
            .entity_selector
            .iter(score_director)
            .map(|r| r.entity_index)
            .collect();

        let route_lens: Vec<usize> = entities.iter().map(|&e| list_len(solution, e)).collect();
        let total_elements: usize = route_lens.iter().sum();

        /* Approximate: each element can move to any position in any entity
        Intra: ~m positions per entity
        Inter: ~(n-1) * m positions
        */
        let n = entities.len();
        if n == 0 || total_elements == 0 {
            return 0;
        }

        let avg_len = total_elements / n;
        // Intra moves: n * m * m
        // Inter moves: n * (n-1) * m * m
        n * avg_len * (avg_len + (n - 1) * avg_len)
    }
}