/*
 * 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.
 */
package org.apache.lucene.queries.function.valuesource;

import java.io.IOException;
import java.util.Map;
import org.apache.lucene.index.DocValues;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.MultiTerms;
import org.apache.lucene.index.ReaderUtil;
import org.apache.lucene.index.SortedDocValues;
import org.apache.lucene.index.Terms;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.queries.function.FunctionValues;
import org.apache.lucene.queries.function.docvalues.IntDocValues;
import org.apache.lucene.util.BytesRef;

/**
 * Use a field value and find the Document Frequency within another field.
 *
 * @since solr 4.0
 */
public class JoinDocFreqValueSource extends FieldCacheSource {

  public static final String NAME = "joindf";

  protected final String qfield;

  public JoinDocFreqValueSource(String field, String qfield) {
    super(field);
    this.qfield = qfield;
  }

  @Override
  public String description() {
    return NAME + "(" + field + ":(" + qfield + "))";
  }

  @Override
  public FunctionValues getValues(Map<Object, Object> context, LeafReaderContext readerContext)
      throws IOException {
    final SortedDocValues terms = DocValues.getSorted(readerContext.reader(), field);
    final IndexReader top = ReaderUtil.getTopLevelContext(readerContext).reader();
    Terms t = MultiTerms.getTerms(top, qfield);
    final TermsEnum termsEnum = t == null ? TermsEnum.EMPTY : t.iterator();

    return new IntDocValues(this) {

      int lastDocID = -1;

      @Override
      public int intVal(int doc) throws IOException {
        if (doc < lastDocID) {
          throw new IllegalArgumentException(
              "docs were sent out-of-order: lastDocID=" + lastDocID + " vs docID=" + doc);
        }
        lastDocID = doc;
        int curDocID = terms.docID();
        if (doc > curDocID) {
          curDocID = terms.advance(doc);
        }
        if (doc == curDocID) {
          BytesRef term = terms.lookupOrd(terms.ordValue());
          if (termsEnum.seekExact(term)) {
            return termsEnum.docFreq();
          }
        }
        return 0;
      }
    };
  }

  @Override
  public boolean equals(Object o) {
    if (o.getClass() != JoinDocFreqValueSource.class) return false;
    JoinDocFreqValueSource other = (JoinDocFreqValueSource) o;
    if (!qfield.equals(other.qfield)) return false;
    return super.equals(other);
  }

  @Override
  public int hashCode() {
    return qfield.hashCode() + super.hashCode();
  }
}
