public void init(SolrParams params) {
   this.params = params;
   String[] fields = params.getParams(TermsParams.TERMS_FIELD);
   if (fields != null) {
     for (String field : fields) {
       // TODO: not sure 128 is the best starting size
       // It use it because that is what is used for facets
       fieldmap.put(field, new HashMap<String, TermsResponse.Term>(128));
     }
   }
 }
 int resolveRegexpFlags(SolrParams params) {
   String[] flagParams = params.getParams(TermsParams.TERMS_REGEXP_FLAG);
   if (flagParams == null) {
     return 0;
   }
   int flags = 0;
   for (String flagParam : flagParams) {
     try {
       flags |= TermsParams.TermsRegexpFlag.valueOf(flagParam.toUpperCase(Locale.ROOT)).getValue();
     } catch (IllegalArgumentException iae) {
       throw new SolrException(
           SolrException.ErrorCode.BAD_REQUEST, "Unknown terms regex flag '" + flagParam + "'");
     }
   }
   return flags;
 }
  @Override
  public void process(ResponseBuilder rb) throws IOException {
    SolrParams params = rb.req.getParams();
    if (!params.getBool(TermsParams.TERMS, false)) return;

    String[] fields = params.getParams(TermsParams.TERMS_FIELD);

    NamedList<Object> termsResult = new SimpleOrderedMap<>();
    rb.rsp.add("terms", termsResult);

    if (fields == null || fields.length == 0) return;

    int limit = params.getInt(TermsParams.TERMS_LIMIT, 10);
    if (limit < 0) {
      limit = Integer.MAX_VALUE;
    }

    String lowerStr = params.get(TermsParams.TERMS_LOWER);
    String upperStr = params.get(TermsParams.TERMS_UPPER);
    boolean upperIncl = params.getBool(TermsParams.TERMS_UPPER_INCLUSIVE, false);
    boolean lowerIncl = params.getBool(TermsParams.TERMS_LOWER_INCLUSIVE, true);
    boolean sort =
        !TermsParams.TERMS_SORT_INDEX.equals(
            params.get(TermsParams.TERMS_SORT, TermsParams.TERMS_SORT_COUNT));
    int freqmin = params.getInt(TermsParams.TERMS_MINCOUNT, 1);
    int freqmax = params.getInt(TermsParams.TERMS_MAXCOUNT, UNLIMITED_MAX_COUNT);
    if (freqmax < 0) {
      freqmax = Integer.MAX_VALUE;
    }
    String prefix = params.get(TermsParams.TERMS_PREFIX_STR);
    String regexp = params.get(TermsParams.TERMS_REGEXP_STR);
    Pattern pattern = regexp != null ? Pattern.compile(regexp, resolveRegexpFlags(params)) : null;

    boolean raw = params.getBool(TermsParams.TERMS_RAW, false);

    final AtomicReader indexReader = rb.req.getSearcher().getAtomicReader();
    Fields lfields = indexReader.fields();

    for (String field : fields) {
      NamedList<Integer> fieldTerms = new NamedList<>();
      termsResult.add(field, fieldTerms);

      Terms terms = lfields == null ? null : lfields.terms(field);
      if (terms == null) {
        // no terms for this field
        continue;
      }

      FieldType ft = raw ? null : rb.req.getSchema().getFieldTypeNoEx(field);
      if (ft == null) ft = new StrField();

      // prefix must currently be text
      BytesRef prefixBytes = prefix == null ? null : new BytesRef(prefix);

      BytesRef upperBytes = null;
      if (upperStr != null) {
        upperBytes = new BytesRef();
        ft.readableToIndexed(upperStr, upperBytes);
      }

      BytesRef lowerBytes;
      if (lowerStr == null) {
        // If no lower bound was specified, use the prefix
        lowerBytes = prefixBytes;
      } else {
        lowerBytes = new BytesRef();
        if (raw) {
          // TODO: how to handle binary? perhaps we don't for "raw"... or if the field exists
          // perhaps we detect if the FieldType is non-character and expect hex if so?
          lowerBytes = new BytesRef(lowerStr);
        } else {
          lowerBytes = new BytesRef();
          ft.readableToIndexed(lowerStr, lowerBytes);
        }
      }

      TermsEnum termsEnum = terms.iterator(null);
      BytesRef term = null;

      if (lowerBytes != null) {
        if (termsEnum.seekCeil(lowerBytes) == TermsEnum.SeekStatus.END) {
          termsEnum = null;
        } else {
          term = termsEnum.term();
          // Only advance the enum if we are excluding the lower bound and the lower Term actually
          // matches
          if (lowerIncl == false && term.equals(lowerBytes)) {
            term = termsEnum.next();
          }
        }
      } else {
        // position termsEnum on first term
        term = termsEnum.next();
      }

      int i = 0;
      BoundedTreeSet<CountPair<BytesRef, Integer>> queue =
          (sort ? new BoundedTreeSet<CountPair<BytesRef, Integer>>(limit) : null);
      CharsRef external = new CharsRef();
      while (term != null && (i < limit || sort)) {
        boolean externalized = false; // did we fill in "external" yet for this term?

        // stop if the prefix doesn't match
        if (prefixBytes != null && !StringHelper.startsWith(term, prefixBytes)) break;

        if (pattern != null) {
          // indexed text or external text?
          // TODO: support "raw" mode?
          ft.indexedToReadable(term, external);
          externalized = true;
          if (!pattern.matcher(external).matches()) {
            term = termsEnum.next();
            continue;
          }
        }

        if (upperBytes != null) {
          int upperCmp = term.compareTo(upperBytes);
          // if we are past the upper term, or equal to it (when don't include upper) then stop.
          if (upperCmp > 0 || (upperCmp == 0 && !upperIncl)) break;
        }

        // This is a good term in the range.  Check if mincount/maxcount conditions are satisfied.
        int docFreq = termsEnum.docFreq();
        if (docFreq >= freqmin && docFreq <= freqmax) {
          // add the term to the list
          if (sort) {
            queue.add(new CountPair<>(BytesRef.deepCopyOf(term), docFreq));
          } else {

            // TODO: handle raw somehow
            if (!externalized) {
              ft.indexedToReadable(term, external);
            }
            fieldTerms.add(external.toString(), docFreq);
            i++;
          }
        }

        term = termsEnum.next();
      }

      if (sort) {
        for (CountPair<BytesRef, Integer> item : queue) {
          if (i >= limit) break;
          ft.indexedToReadable(item.key, external);
          fieldTerms.add(external.toString(), item.val);
          i++;
        }
      }
    }
  }