package org.apache.lucene.queries;

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.lucene.index.*;
import org.apache.lucene.search.DocIdSet;
import org.apache.lucene.search.DocIdSetIterator;
import org.apache.lucene.search.Filter;
import org.apache.lucene.util.Bits;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.FixedBitSet;

import java.io.IOException;
import java.util.Set;
import java.util.TreeSet;

/**
 * Constructs a filter for docs matching any of the terms added to this class.
 * Unlike a RangeFilter this can be used for filtering on multiple terms that are not necessarily in
 * a sequence. An example might be a collection of primary keys from a database query result or perhaps
 * a choice of "category" labels picked by the end user. As a filter, this is much faster than the
 * equivalent query (a BooleanQuery with many "should" TermQueries)
 */
public class TermsFilter extends Filter {

  private final Set<Term> terms = new TreeSet<Term>();

  /**
   * Adds a term to the list of acceptable terms
   */
  public void addTerm(Term term) {
    terms.add(term);
  }

/* (non-Javadoc)
   * @see org.apache.lucene.search.Filter#getDocIdSet(org.apache.lucene.index.IndexReader)
   */

  @Override
  public DocIdSet getDocIdSet(AtomicReaderContext context, Bits acceptDocs) throws IOException {
    AtomicReader reader = context.reader();
    FixedBitSet result = new FixedBitSet(reader.maxDoc());
    Fields fields = reader.fields();

    if (fields == null) {
      return result;
    }

    BytesRef br = new BytesRef();
    String lastField = null;
    Terms termsC;
    TermsEnum termsEnum = null;
    DocsEnum docs = null;
    for (Term term : terms) {
      if (!term.field().equals(lastField)) {
        termsC = fields.terms(term.field());
        if (termsC == null) {
          return result;
        }
        termsEnum = termsC.iterator(null);
        lastField = term.field();
      }

      if (terms != null) { // TODO this check doesn't make sense, decide which variable its supposed to be for
        br.copyBytes(term.bytes());
        assert termsEnum != null;
        if (termsEnum.seekCeil(br) == TermsEnum.SeekStatus.FOUND) {
          docs = termsEnum.docs(acceptDocs, docs, 0);
          while (docs.nextDoc() != DocIdSetIterator.NO_MORE_DOCS) {
            result.set(docs.docID());
          }
        }
      }
    }
    return result;
  }

  @Override
  public boolean equals(Object obj) {
    if (this == obj) {
      return true;
    }
    if ((obj == null) || (obj.getClass() != this.getClass())) {
      return false;
    }

    TermsFilter test = (TermsFilter) obj;
    return (terms == test.terms ||
        (terms != null && terms.equals(test.terms)));
  }

  @Override
  public int hashCode() {
    int hash = 9;
    for (Term term : terms) {
      hash = 31 * hash + term.hashCode();
    }
    return hash;
  }

}