ktg-plugin-marketplace/plugins/voyage/lib/parsers/jaccard.mjs

// lib/parsers/jaccard.mjs
// Jaccard similarity for SC4 determinism floor.
//
// jaccard(A, B) = |A ∩ B| / |A ∪ B|
// Inputs are arrays of strings; deduplicated internally.
// Both empty → 1.0 (vacuously identical). One empty → 0.0.

/**
 * Compute Jaccard similarity between two string sets.
 * @param {string[]} setA
 * @param {string[]} setB
 * @returns {number} similarity in [0, 1]
 */
export function jaccardSimilarity(setA, setB) {
  if (!Array.isArray(setA) || !Array.isArray(setB)) {
    throw new TypeError('jaccardSimilarity: both inputs must be arrays');
  }
  const a = new Set(setA);
  const b = new Set(setB);
  if (a.size === 0 && b.size === 0) return 1.0;
  if (a.size === 0 || b.size === 0) return 0.0;

  let intersection = 0;
  for (const x of a) {
    if (b.has(x)) intersection += 1;
  }
  const union = a.size + b.size - intersection;
  return intersection / union;
}

/**
 * Check whether a similarity meets a threshold.
 * @param {number} similarity
 * @param {number} threshold
 * @returns {boolean}
 */
export function meetsThreshold(similarity, threshold) {
  if (typeof similarity !== 'number' || typeof threshold !== 'number') return false;
  if (!Number.isFinite(similarity) || !Number.isFinite(threshold)) return false;
  return similarity >= threshold;
}