cupel 1.2.0

Context window management pipeline for LLM applications
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use crate::model::ContextItem;
use crate::scorer::Scorer;

/// Relative scorer: proportion of peers sharing at least one tag.
///
/// Self-exclusion uses reference identity (`std::ptr::eq`).
/// Tag comparison is case-insensitive (ASCII fold).
///
/// # Examples
///
/// ```
/// use cupel::{ContextItemBuilder, FrequencyScorer, Scorer};
///
/// let a = ContextItemBuilder::new("first", 5)
///     .tags(vec!["topic-a".to_string()])
///     .build()?;
/// let b = ContextItemBuilder::new("second", 5)
///     .tags(vec!["topic-a".to_string()])
///     .build()?;
///
/// let items = vec![a, b];
/// // Pass a reference into the vec — FrequencyScorer uses ptr identity for self-exclusion
/// let score = FrequencyScorer.score(&items[0], &items);
/// assert_eq!(score, 1.0); // 1 of 1 non-self peer shares a tag
/// # Ok::<(), cupel::CupelError>(())
/// ```
#[derive(Debug, Clone, Copy)]
pub struct FrequencyScorer;

impl Scorer for FrequencyScorer {
    fn score(&self, item: &ContextItem, all_items: &[ContextItem]) -> f64 {
        if item.tags().is_empty() || all_items.len() <= 1 {
            return 0.0;
        }

        let mut matching_items: usize = 0;

        for other in all_items {
            // Self-exclusion by reference identity
            if std::ptr::eq(item, other) {
                continue;
            }
            if other.tags().is_empty() {
                continue;
            }
            if shares_any_tag(item.tags(), other.tags()) {
                matching_items += 1;
            }
        }

        matching_items as f64 / (all_items.len() - 1) as f64
    }
}

/// Checks if two tag slices share any tag using case-insensitive ASCII comparison.
fn shares_any_tag(tags_a: &[String], tags_b: &[String]) -> bool {
    for a in tags_a {
        for b in tags_b {
            if a.eq_ignore_ascii_case(b) {
                return true;
            }
        }
    }
    false
}