transient sclass DeepBitSetWordIndex<A> {

  S regexp = "\\w+";

  new Map<A, SingleTextWordIndex> singleTextIndices;

  new ElementInstanceMatrix<A, S> mainIndex;

  void add(A a, S text) {

    singleTextIndices.put(a, new SingleTextWordIndex(regexp, text));

    mainIndex.add(a, mapToSet upper(regexpExtractAll(regexp, text));

  }

  void doneAdding {

    mainIndex.doneAdding();

  }

  LPair<S, Int> wordsAndOffsets(S text) {

    ret map(regexpFindRanges(regexp, text),

      r -> pair(upper(substring(text, r)), r.start));

  }

  // assumes word boundaries left and right of query

  Cl<A> preSearch(S query, O... _) {

    optPar bool debug;

    LPair<S, Int> l = wordsAndOffsets(query);

    Cl<A> candidates = mainIndex.instancesContainingAllElements(pairsA(l));

    if (debug) {

      L<Int> lengths = map(candidates, a -> singleTextIndices.get(a).length);

      print(nCandidates(candidates) + ", total length: " + n2(intSum(lengths)) + ", lengths: " + lengths);

    }

    ret filter(candidates, a -> nempty(singleTextIndices.get(a).indicesOfWordCombination(l)));

  }

  int numWords() { ret mainIndex.numElements(); }

}