// returns a prefiltered list of elements; you still need to do a

// full-text search on those.

// If it returns null, you have to search all elements

static <A> Iterable<A> deepDoubleWordIndex_lookupString(DoubleWordIndex<WithIntArray<A>> index, S query, O... _) {

  optPar bool debug;

  L<IntRange> ranges = index.wordRanges(query);

  if (empty(ranges)) null;

  int nRanges = l(ranges);

  new Map<A, MultiSetMap<Int>> theMap; // for every snippet, a map of string position to word index

  Set<A> baseSet = null;

  for (int iWord = 1; iWord < nRanges-1; iWord++) { // go through all "full" words

    IntRange r = ranges.get(iWord);

    S word = substring(query, r);

    Set<WithIntArray<A>> entries = index.index1.get(word);

    baseSet = intersectSets_nullIsFull(baseSet, getVarsToSet(entries));

  }

  if (baseSet != null) {

    print("baseSet: " + l(baseSet));

    ret baseSet;

  }

  // special case, just a single word in query

  if (l(ranges) == 1 && first(ranges).start == 0 && first(ranges).end == l(query)) {

    new Set<A> seen;

    ret nestedIterator(containingIC(index.index1.words(), query), fullWord ->

      mapI_nonNulls_if1(index.index1.get(fullWord), e -> addAndReturnIfNew(seen, e!)));

  }

  for iWord over ranges: { // go through words in query

    IntRange r = ranges.get(iWord);

    S word = substring(query, r);

    Cl<S> l; // all matching words in index

    WordIndex<WithIntArray<A>> indexToUse = index.index1;

    if (r.start == 0) { // look for ending of word - use reverse index

      l = prefixSubSet(index.index2.words(), reversed(word));

      if (empty(l)) ret emptyList();

      if (debug) print("word=" + word + ", fullWords=" + l);

      // special loop that accounts for length of actual word

      for (S fullWord : l)

        for (WithIntArray<A> entry : index.index2.index.get(fullWord)) {

          if (baseSet != null && !baseSet.contains(entry!)) continue;

          MultiSetMap<Int> msm = theMap.get(entry!);

          if (msm == null) theMap.put(entry!, msm = new MultiSetMap);

          int ofs = l(fullWord)-l(word)-r.start;

          for (int i : entry.array) {

            int idx = i+ofs;

            if (debug) print("Got idx " + idx);

            if (idx >= 0)

              msm.put(idx, iWord);

          }

        }

      continue;

    } else if (r.end == l(query)) { // look for start of word

      l = prefixSubSet(index.index1.words(), word);

    } else // look for complete word

      l = ll(word);

    if (empty(l)) ret emptyList();

    if (debug) print("word=" + word + ", fullWords=" + l);

    for (S fullWord : l)

      for (WithIntArray<A> entry : indexToUse.index.get(fullWord)) {

        if (baseSet != null && !baseSet.contains(entry!)) continue;

        if (debug) print("Got entry " + entry);

        MultiSetMap<Int> msm = theMap.get(entry!);

        if (msm == null) theMap.put(entry!, msm = new MultiSetMap);

        for (int i : entry.array) {

          int idx = i-r.start;

          if (debug) print("Got idx " + idx);

          if (idx >= 0)

            msm.put(idx, iWord);

        }

      }

  }

  if (debug) print("theMap size=" + l(theMap));

  ret asList(mapI_nonNulls_if1(theMap.entrySet(), e -> {

    A snippet = e.getKey();

    MultiSetMap<Int> msm = e.getValue();

    if (debug) print("snippet " + snippet);

    for (int position, Set<Int> wordIndices : msm.data) {

      if (debug) print("position " + position + ": " + l(wordIndices) + "/" + nRanges);

      if (l(wordIndices) == nRanges)

        ret snippet;

    }

    null;

  }));

}