solverforge_scoring/stream/

collection_extract.rs

/* CollectionExtract trait for ergonomic entity collection extraction.

Allows extractor closures to return either `&[A]` or `&Vec<A>`,
so users can write `vec(|s| &s.employees)` without `.as_slice()`.

# Usage

```
use solverforge_scoring::stream::collection_extract::{CollectionExtract, VecExtract, vec};

struct Schedule { employees: Vec<String> }

// Direct slice closure — works out of the box:
let e1 = |s: &Schedule| s.employees.as_slice();
let _: &[String] = e1.extract(&Schedule { employees: vec![] });

// Vec reference closure — wrap with `vec(...)`:
let e2 = vec(|s: &Schedule| &s.employees);
let _: &[String] = e2.extract(&Schedule { employees: vec![] });
```
*/

/* Extracts a slice of entities from the solution.

The associated type `Item` names the entity type, allowing callers to
write `E: CollectionExtract<S, Item = A>` when `A` must be inferred from `E`
rather than stated as a separate generic parameter.
*/
pub trait CollectionExtract<S>: Send + Sync {
    // The entity type yielded by this extractor.
    type Item;

    // Extracts the entity slice from the solution.
    fn extract<'s>(&self, s: &'s S) -> &'s [Self::Item];

    // Identifies whether the solution source owns descriptor-scoped localized updates.
    // Plain extractors are non-localized; wrap them in `source(..., Descriptor(idx))`
    // when they must receive localized mutation callbacks.
    fn change_source(&self) -> ChangeSource {
        ChangeSource::Unknown
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ChangeSource {
    Unknown,
    Static,
    Descriptor(usize),
}

impl ChangeSource {
    #[inline]
    pub fn reacts_to(self, descriptor_index: usize) -> bool {
        match self {
            Self::Unknown => true,
            Self::Static => false,
            Self::Descriptor(index) => index == descriptor_index,
        }
    }

    #[inline]
    pub fn owns_descriptor(self, descriptor_index: usize) -> bool {
        matches!(self, Self::Descriptor(index) if index == descriptor_index)
    }

    #[inline]
    pub fn is_unknown(self) -> bool {
        matches!(self, Self::Unknown)
    }

    #[inline]
    pub fn same_index_domain(self, other: Self) -> bool {
        matches!((self, other), (Self::Descriptor(left), Self::Descriptor(right)) if left == right)
    }

    #[inline]
    pub fn assert_localizes(self, descriptor_index: usize, constraint_name: &str) -> bool {
        if self.owns_descriptor(descriptor_index) {
            return true;
        }
        if self.reacts_to(descriptor_index) {
            panic!(
                "constraint `{constraint_name}` received descriptor {descriptor_index}, but source {self:?} cannot localize entity indexes"
            );
        }
        false
    }
}

pub trait FlattenExtract<P>: Send + Sync {
    type Item;

    fn extract<'s>(&self, parent: &'s P) -> &'s [Self::Item];
}

impl<S, A, F> CollectionExtract<S> for F
where
    F: for<'a> Fn(&'a S) -> &'a [A] + Send + Sync,
{
    type Item = A;

    #[inline]
    fn extract<'s>(&self, s: &'s S) -> &'s [A] {
        self(s)
    }
}

impl<P, B, F> FlattenExtract<P> for F
where
    F: for<'a> Fn(&'a P) -> &'a [B] + Send + Sync,
{
    type Item = B;

    #[inline]
    fn extract<'s>(&self, parent: &'s P) -> &'s [B] {
        self(parent)
    }
}

#[derive(Clone, Copy)]
pub struct FlattenVecExtract<F>(pub F);

impl<P, B, F> FlattenExtract<P> for FlattenVecExtract<F>
where
    F: for<'a> Fn(&'a P) -> &'a Vec<B> + Send + Sync,
{
    type Item = B;

    #[inline]
    fn extract<'s>(&self, parent: &'s P) -> &'s [B] {
        (self.0)(parent).as_slice()
    }
}

#[derive(Clone, Copy)]
pub struct SourceExtract<E> {
    extractor: E,
    change_source: ChangeSource,
}

impl<E> SourceExtract<E> {
    pub fn new(extractor: E, change_source: ChangeSource) -> Self {
        Self {
            extractor,
            change_source,
        }
    }

    pub fn extractor(&self) -> &E {
        &self.extractor
    }
}

impl<S, E> CollectionExtract<S> for SourceExtract<E>
where
    E: CollectionExtract<S>,
{
    type Item = E::Item;

    #[inline]
    fn extract<'s>(&self, s: &'s S) -> &'s [Self::Item] {
        self.extractor.extract(s)
    }

    fn change_source(&self) -> ChangeSource {
        self.change_source
    }
}

/* Wraps a `Fn(&S) -> &Vec<A>` closure so it satisfies `CollectionExtract<S>`.

Construct via the [`vec`] free function.
*/
pub struct VecExtract<F>(pub F);

impl<S, A, F> CollectionExtract<S> for VecExtract<F>
where
    F: for<'a> Fn(&'a S) -> &'a Vec<A> + Send + Sync,
{
    type Item = A;

    #[inline]
    fn extract<'s>(&self, s: &'s S) -> &'s [A] {
        (self.0)(s).as_slice()
    }
}

/* Wraps a `Fn(&S) -> &Vec<A>` closure into a [`VecExtract`] that satisfies
[`CollectionExtract<S>`].

Use this when your solution field is a `Vec<A>` and you want to write
`|s| &s.field` instead of `|s| s.field.as_slice()`.

# Example

```
use solverforge_scoring::stream::collection_extract::{CollectionExtract, vec};

struct Schedule { employees: Vec<String> }

let extractor = vec(|s: &Schedule| &s.employees);
let schedule = Schedule { employees: vec!["Alice".into()] };
assert_eq!(extractor.extract(&schedule), &["Alice".to_string()]);
```
*/
pub fn vec<S, A, F>(f: F) -> VecExtract<F>
where
    F: for<'a> Fn(&'a S) -> &'a Vec<A> + Send + Sync,
{
    VecExtract(f)
}

pub fn source<E>(extractor: E, change_source: ChangeSource) -> SourceExtract<E> {
    SourceExtract::new(extractor, change_source)
}