solverforge-scoring 0.8.3

/* Zero-erasure complemented group constraint.

Evaluates grouped results plus complement entities with default values.
Provides true incremental scoring by tracking per-key accumulators.
*/

use std::collections::HashMap;
use std::hash::Hash;
use std::marker::PhantomData;

use solverforge_core::score::Score;
use solverforge_core::{ConstraintRef, ImpactType};

use crate::api::constraint_set::IncrementalConstraint;
use crate::stream::collector::{Accumulator, UniCollector};

/* Zero-erasure constraint for complemented grouped results.

Groups A entities by key, then iterates over B entities (complement source),
using grouped values where they exist and default values otherwise.

The key function for A returns `Option<K>`, allowing entities to be skipped
when they don't have a valid key (e.g., unassigned shifts).

# Type Parameters

- `S` - Solution type
- `A` - Entity type being grouped (e.g., Shift)
- `B` - Complement entity type (e.g., Employee)
- `K` - Group key type
- `EA` - Extractor for A entities
- `EB` - Extractor for B entities
- `KA` - Key function for A (returns `Option<K>` to allow skipping)
- `KB` - Key function for B
- `C` - Collector type
- `D` - Default value function
- `W` - Weight function
- `Sc` - Score type

# Example

```
use solverforge_scoring::constraint::complemented::ComplementedGroupConstraint;
use solverforge_scoring::stream::collector::count;
use solverforge_scoring::api::constraint_set::IncrementalConstraint;
use solverforge_core::{ConstraintRef, ImpactType};
use solverforge_core::score::SoftScore;

#[derive(Clone, Hash, PartialEq, Eq)]
struct Employee { id: usize }

#[derive(Clone)]
struct Shift { employee_id: Option<usize> }

#[derive(Clone)]
struct Schedule {
employees: Vec<Employee>,
shifts: Vec<Shift>,
}

let constraint = ComplementedGroupConstraint::new(
ConstraintRef::new("", "Shift count"),
ImpactType::Penalty,
|s: &Schedule| s.shifts.as_slice(),
|s: &Schedule| s.employees.as_slice(),
|shift: &Shift| shift.employee_id,  // Returns Option<usize>
|emp: &Employee| emp.id,
count(),
|_emp: &Employee| 0usize,
|count: &usize| SoftScore::of(*count as i64),
false,
);

let schedule = Schedule {
employees: vec![Employee { id: 0 }, Employee { id: 1 }],
shifts: vec![
Shift { employee_id: Some(0) },
Shift { employee_id: Some(0) },
Shift { employee_id: None },  // Skipped - no key
],
};

// Employee 0: 2 shifts, Employee 1: 0 shifts → Total: -2
// Unassigned shift is skipped
assert_eq!(constraint.evaluate(&schedule), SoftScore::of(-2));
```
*/
pub struct ComplementedGroupConstraint<S, A, B, K, EA, EB, KA, KB, C, D, W, Sc>
where
    C: UniCollector<A>,
    Sc: Score,
{
    constraint_ref: ConstraintRef,
    impact_type: ImpactType,
    extractor_a: EA,
    extractor_b: EB,
    key_a: KA,
    key_b: KB,
    collector: C,
    default_fn: D,
    weight_fn: W,
    is_hard: bool,
    // Group key -> accumulator for incremental scoring
    groups: HashMap<K, C::Accumulator>,
    // A entity index -> group key (for tracking which group each entity belongs to)
    entity_groups: HashMap<usize, K>,
    // A entity index -> extracted value (for correct retraction after entity mutation)
    entity_values: HashMap<usize, C::Value>,
    // B key -> B entity index (for looking up B entities by key)
    b_by_key: HashMap<K, usize>,
    _phantom: PhantomData<(fn() -> S, fn() -> A, fn() -> B, fn() -> Sc)>,
}

impl<S, A, B, K, EA, EB, KA, KB, C, D, W, Sc>
    ComplementedGroupConstraint<S, A, B, K, EA, EB, KA, KB, C, D, W, Sc>
where
    S: 'static,
    A: Clone + 'static,
    B: Clone + 'static,
    K: Clone + Eq + Hash,
    EA: crate::stream::collection_extract::CollectionExtract<S, Item = A>,
    EB: crate::stream::collection_extract::CollectionExtract<S, Item = B>,
    KA: Fn(&A) -> Option<K>,
    KB: Fn(&B) -> K,
    C: UniCollector<A>,
    C::Result: Clone,
    D: Fn(&B) -> C::Result,
    W: Fn(&C::Result) -> Sc,
    Sc: Score,
{
    // Creates a new complemented group constraint.
    #[allow(clippy::too_many_arguments)]
    pub fn new(
        constraint_ref: ConstraintRef,
        impact_type: ImpactType,
        extractor_a: EA,
        extractor_b: EB,
        key_a: KA,
        key_b: KB,
        collector: C,
        default_fn: D,
        weight_fn: W,
        is_hard: bool,
    ) -> Self {
        Self {
            constraint_ref,
            impact_type,
            extractor_a,
            extractor_b,
            key_a,
            key_b,
            collector,
            default_fn,
            weight_fn,
            is_hard,
            groups: HashMap::new(),
            entity_groups: HashMap::new(),
            entity_values: HashMap::new(),
            b_by_key: HashMap::new(),
            _phantom: PhantomData,
        }
    }

    #[inline]
    fn compute_score(&self, result: &C::Result) -> Sc {
        let base = (self.weight_fn)(result);
        match self.impact_type {
            ImpactType::Penalty => -base,
            ImpactType::Reward => base,
        }
    }

    // Build grouped results from A entities.
    fn build_groups(&self, entities_a: &[A]) -> HashMap<K, C::Result> {
        let mut accumulators: HashMap<K, C::Accumulator> = HashMap::new();

        for a in entities_a {
            // Skip entities with no key (e.g., unassigned shifts)
            let Some(key) = (self.key_a)(a) else {
                continue;
            };
            let value = self.collector.extract(a);
            accumulators
                .entry(key)
                .or_insert_with(|| self.collector.create_accumulator())
                .accumulate(&value);
        }

        accumulators
            .into_iter()
            .map(|(k, acc)| (k, acc.finish()))
            .collect()
    }
}

impl<S, A, B, K, EA, EB, KA, KB, C, D, W, Sc> IncrementalConstraint<S, Sc>
    for ComplementedGroupConstraint<S, A, B, K, EA, EB, KA, KB, C, D, W, Sc>
where
    S: Send + Sync + 'static,
    A: Clone + Send + Sync + 'static,
    B: Clone + Send + Sync + 'static,
    K: Clone + Eq + Hash + Send + Sync,
    EA: crate::stream::collection_extract::CollectionExtract<S, Item = A>,
    EB: crate::stream::collection_extract::CollectionExtract<S, Item = B>,
    KA: Fn(&A) -> Option<K> + Send + Sync,
    KB: Fn(&B) -> K + Send + Sync,
    C: UniCollector<A> + Send + Sync,
    C::Accumulator: Send + Sync,
    C::Result: Clone + Send + Sync,
    C::Value: Send + Sync,
    D: Fn(&B) -> C::Result + Send + Sync,
    W: Fn(&C::Result) -> Sc + Send + Sync,
    Sc: Score,
{
    fn evaluate(&self, solution: &S) -> Sc {
        let entities_a = self.extractor_a.extract(solution);
        let entities_b = self.extractor_b.extract(solution);

        let groups = self.build_groups(entities_a);

        let mut total = Sc::zero();
        for b in entities_b {
            let key = (self.key_b)(b);
            let result = groups
                .get(&key)
                .cloned()
                .unwrap_or_else(|| (self.default_fn)(b));
            total = total + self.compute_score(&result);
        }

        total
    }

    fn match_count(&self, solution: &S) -> usize {
        let entities_b = self.extractor_b.extract(solution);
        entities_b.len()
    }

    fn initialize(&mut self, solution: &S) -> Sc {
        self.reset();

        let entities_a = self.extractor_a.extract(solution);
        let entities_b = self.extractor_b.extract(solution);

        // Build B key -> index mapping
        for (idx, b) in entities_b.iter().enumerate() {
            let key = (self.key_b)(b);
            self.b_by_key.insert(key, idx);
        }

        // Initialize all B entities with default scores
        let mut total = Sc::zero();
        for b in entities_b {
            let default_result = (self.default_fn)(b);
            total = total + self.compute_score(&default_result);
        }

        // Now insert all A entities incrementally
        for (idx, a) in entities_a.iter().enumerate() {
            total = total + self.insert_entity(entities_b, idx, a);
        }

        total
    }

    fn on_insert(&mut self, solution: &S, entity_index: usize, _descriptor_index: usize) -> Sc {
        let entities_a = self.extractor_a.extract(solution);
        let entities_b = self.extractor_b.extract(solution);

        if entity_index >= entities_a.len() {
            return Sc::zero();
        }

        let entity = &entities_a[entity_index];
        self.insert_entity(entities_b, entity_index, entity)
    }

    fn on_retract(&mut self, solution: &S, entity_index: usize, _descriptor_index: usize) -> Sc {
        let entities_a = self.extractor_a.extract(solution);
        let entities_b = self.extractor_b.extract(solution);

        self.retract_entity(entities_a, entities_b, entity_index)
    }

    fn reset(&mut self) {
        self.groups.clear();
        self.entity_groups.clear();
        self.entity_values.clear();
        self.b_by_key.clear();
    }

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

    fn is_hard(&self) -> bool {
        self.is_hard
    }

    fn constraint_ref(&self) -> ConstraintRef {
        self.constraint_ref.clone()
    }
}

impl<S, A, B, K, EA, EB, KA, KB, C, D, W, Sc>
    ComplementedGroupConstraint<S, A, B, K, EA, EB, KA, KB, C, D, W, Sc>
where
    S: Send + Sync + 'static,
    A: Clone + Send + Sync + 'static,
    B: Clone + Send + Sync + 'static,
    K: Clone + Eq + Hash + Send + Sync,
    EA: crate::stream::collection_extract::CollectionExtract<S, Item = A>,
    EB: crate::stream::collection_extract::CollectionExtract<S, Item = B>,
    KA: Fn(&A) -> Option<K> + Send + Sync,
    KB: Fn(&B) -> K + Send + Sync,
    C: UniCollector<A> + Send + Sync,
    C::Accumulator: Send + Sync,
    C::Result: Clone + Send + Sync,
    C::Value: Send + Sync,
    D: Fn(&B) -> C::Result + Send + Sync,
    W: Fn(&C::Result) -> Sc + Send + Sync,
    Sc: Score,
{
    // Insert an A entity and return the score delta.
    fn insert_entity(&mut self, entities_b: &[B], entity_index: usize, entity: &A) -> Sc {
        // Skip entities with no key (e.g., unassigned shifts)
        let Some(key) = (self.key_a)(entity) else {
            return Sc::zero();
        };
        let value = self.collector.extract(entity);
        let impact = self.impact_type;

        // Check if there's a B entity for this key
        let b_idx = self.b_by_key.get(&key).copied();
        let Some(b_idx) = b_idx else {
            // No B entity for this key - A entity doesn't affect score
            // Still track it for retraction
            let acc = self
                .groups
                .entry(key.clone())
                .or_insert_with(|| self.collector.create_accumulator());
            acc.accumulate(&value);
            self.entity_groups.insert(entity_index, key);
            self.entity_values.insert(entity_index, value);
            return Sc::zero();
        };

        let b = &entities_b[b_idx];

        // Compute old score for this B entity
        let old_result = self
            .groups
            .get(&key)
            .map(|acc| acc.finish())
            .unwrap_or_else(|| (self.default_fn)(b));
        let old_base = (self.weight_fn)(&old_result);
        let old = match impact {
            ImpactType::Penalty => -old_base,
            ImpactType::Reward => old_base,
        };

        // Get or create accumulator and add value
        let acc = self
            .groups
            .entry(key.clone())
            .or_insert_with(|| self.collector.create_accumulator());
        acc.accumulate(&value);

        // Compute new score
        let new_result = acc.finish();
        let new_base = (self.weight_fn)(&new_result);
        let new_score = match impact {
            ImpactType::Penalty => -new_base,
            ImpactType::Reward => new_base,
        };

        // Track entity -> key mapping and cache value for correct retraction
        self.entity_groups.insert(entity_index, key);
        self.entity_values.insert(entity_index, value);

        // Return delta
        new_score - old
    }

    // Retract an A entity and return the score delta.
    fn retract_entity(&mut self, _entities_a: &[A], _entities_b: &[B], entity_index: usize) -> Sc {
        // Find which group this entity belonged to
        let Some(key) = self.entity_groups.remove(&entity_index) else {
            return Sc::zero();
        };

        // Use cached value (entity may have been mutated since insert)
        let Some(value) = self.entity_values.remove(&entity_index) else {
            return Sc::zero();
        };
        let impact = self.impact_type;

        // Check if there's a B entity for this key
        let b_idx = self.b_by_key.get(&key).copied();
        if b_idx.is_none() {
            // No B entity for this key - just update accumulator, no score delta
            if let Some(acc) = self.groups.get_mut(&key) {
                acc.retract(&value);
            }
            return Sc::zero();
        }

        // Get accumulator
        let Some(acc) = self.groups.get_mut(&key) else {
            return Sc::zero();
        };

        // Compute old score
        let old_result = acc.finish();
        let old_base = (self.weight_fn)(&old_result);
        let old = match impact {
            ImpactType::Penalty => -old_base,
            ImpactType::Reward => old_base,
        };

        // Retract value
        acc.retract(&value);

        // Compute new score
        let new_result = acc.finish();
        let new_base = (self.weight_fn)(&new_result);
        let new_score = match impact {
            ImpactType::Penalty => -new_base,
            ImpactType::Reward => new_base,
        };

        // Return delta
        new_score - old
    }
}

impl<S, A, B, K, EA, EB, KA, KB, C, D, W, Sc> std::fmt::Debug
    for ComplementedGroupConstraint<S, A, B, K, EA, EB, KA, KB, C, D, W, Sc>
where
    C: UniCollector<A>,
    Sc: Score,
{
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("ComplementedGroupConstraint")
            .field("name", &self.constraint_ref.name)
            .field("impact_type", &self.impact_type)
            .field("groups", &self.groups.len())
            .finish()
    }
}