map.put(FieldNames.DOC_FREQ, docFreq);
        map.put(FieldNames.USER_BOOST, userBoost);
        map.put(FieldNames.SCORE, (queryFreq + docFreq) * userBoost);
        map.put(FieldNames.TIMESTAMP, timestamp.toInstant().toEpochMilli());
        return map;
    }

    /**
     * Parses a source map and returns a SuggestItem instance.
     * @param source The source map.
     * @return A SuggestItem instance.
     */

    public SuggestDeleteResponse deleteOldWords(final ZonedDateTime threshold) {
        final long start = System.currentTimeMillis();
        final String query = FieldNames.TIMESTAMP + ":[* TO " + threshold.toInstant().toEpochMilli() + "] NOT " + FieldNames.KINDS + ':'
                + SuggestItem.Kind.USER;
        deleteByQuery(query);
        return new SuggestDeleteResponse(null, System.currentTimeMillis() - start);
    }

    /**