function termFreq(text) {
  const words = text.toLowerCase().match(/\w+/g) || [];
  const freq = {};
  words.forEach(w => freq[w] = (freq[w] || 0) + 1);
  return freq;
}

export function cosineSimilarity(textA, textB) {
  const fA = termFreq(textA);
  const fB = termFreq(textB);
  const words = new Set([...Object.keys(fA), ...Object.keys(fB)]);
  let dot = 0, magA = 0, magB = 0;

  words.forEach(w => {
    const a = fA[w] || 0;
    const b = fB[w] || 0;
    dot += a * b;
    magA += a * a;
    magB += b * b;
  });

  if (!magA || !magB) return 0;
  return dot / (Math.sqrt(magA) * Math.sqrt(magB));
}

export function searchChunks(query, chunks, topK = 2) {
  if (!chunks || chunks.length === 0) return [];
  return chunks
    .map(c => ({ text: c, score: cosineSimilarity(query, c) }))
    .sort((a, b) => b.score - a.score)
    .slice(0, topK)
    .map(item => item.text);
}