/**
 * Copyright 2014 National University of Ireland, Galway.
 *
 * This file is part of the SIREn project. Project and contact information:
 *
 *  https://github.com/rdelbru/SIREn
 *
 * Licensed 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.sindice.siren.search.node;

import java.io.IOException;
import java.util.Comparator;

import org.apache.lucene.index.AtomicReaderContext;
import org.apache.lucene.index.Fields;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.IndexReaderContext;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermContext;
import org.apache.lucene.index.Terms;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.search.Query;
import org.apache.lucene.util.AttributeSource;
import org.apache.lucene.util.BytesRef;
import org.sindice.siren.search.node.MultiNodeTermQuery.RewriteMethod;

/**
 * Abstract class for rewrite methods.
 *
 * <p>
 *
 * Code taken from {@link TermCollectingRewrite} and adapted for SIREn.
 */
abstract class NodeTermCollectingRewrite<Q extends Query> extends RewriteMethod {

  /** Return a suitable top-level Query for holding all expanded terms. */
  protected abstract Q getTopLevelQuery() throws IOException;

  /** Add a MultiTermQuery term to the top-level query */
  protected final void addClause(final Q topLevel, final Term term, final int docCount, final float boost)
  throws IOException {
    this.addClause(topLevel, term, docCount, boost, null);
  }

  protected abstract void addClause(Q topLevel, Term term, int docCount,
                                    float boost, TermContext states)
  throws IOException;

  final void collectTerms(final IndexReader reader,
                          final MultiNodeTermQuery query,
                          final TermCollector collector)
  throws IOException {
    final IndexReaderContext topReaderContext = reader.getContext();
    Comparator<BytesRef> lastTermComp = null;
    for (final AtomicReaderContext context : topReaderContext.leaves()) {
      final Fields fields = context.reader().fields();
      if (fields == null) {
        // reader has no fields
        continue;
      }

      final Terms terms = fields.terms(query.field);
      if (terms == null) {
        // field does not exist
        continue;
      }

      final TermsEnum termsEnum = this.getTermsEnum(query, terms, collector.attributes);
      assert termsEnum != null;

      if (termsEnum == TermsEnum.EMPTY)
        continue;

      // Check comparator compatibility:
      final Comparator<BytesRef> newTermComp = termsEnum.getComparator();
      if (lastTermComp != null && newTermComp != null && newTermComp != lastTermComp)
        throw new RuntimeException("term comparator should not change between segments: "+lastTermComp+" != "+newTermComp);
      lastTermComp = newTermComp;
      collector.setReaderContext(topReaderContext, context);
      collector.setNextEnum(termsEnum);
      BytesRef bytes;
      while ((bytes = termsEnum.next()) != null) {
        if (!collector.collect(bytes))
          return; // interrupt whole term collection, so also don't iterate other subReaders
      }
    }
  }

  static abstract class TermCollector
  {
    protected AtomicReaderContext readerContext;
    protected IndexReaderContext topReaderContext;

    public void setReaderContext(final IndexReaderContext topReaderContext,
                                 final AtomicReaderContext readerContext) {
      this.readerContext = readerContext;
      this.topReaderContext = topReaderContext;
    }

    /** attributes used for communication with the enum */
    public final AttributeSource attributes = new AttributeSource();

    /** return false to stop collecting */
    public abstract boolean collect(BytesRef bytes) throws IOException;

    /** the next segment's {@link TermsEnum} that is used to collect terms */
    public abstract void setNextEnum(TermsEnum termsEnum) throws IOException;
  }

}