/*
 * 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.codecs;

import java.io.Closeable;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.lucene.index.DocIDMerger;
import org.apache.lucene.index.FieldInfo;
import org.apache.lucene.index.MergeState;
import org.apache.lucene.index.NumericDocValues;
import org.apache.lucene.index.SegmentWriteState;

/**
 * Abstract API that consumes normalization values. Concrete implementations of this actually do
 * "something" with the norms (write it into the index in a specific format).
 *
 * <p>The lifecycle is:
 *
 * <ol>
 *   <li>NormsConsumer is created by {@link NormsFormat#normsConsumer(SegmentWriteState)}.
 *   <li>{@link #addNormsField} is called for each field with normalization values. The API is a
 *       "pull" rather than "push", and the implementation is free to iterate over the values
 *       multiple times ({@link Iterable#iterator()}).
 *   <li>After all fields are added, the consumer is {@link #close}d.
 * </ol>
 *
 * @lucene.experimental
 */
public abstract class NormsConsumer implements Closeable {

  /** Sole constructor. (For invocation by subclass constructors, typically implicit.) */
  protected NormsConsumer() {}

  /**
   * Writes normalization values for a field.
   *
   * @param field field information
   * @param normsProducer NormsProducer of the numeric norm values
   * @throws IOException if an I/O error occurred.
   */
  public abstract void addNormsField(FieldInfo field, NormsProducer normsProducer)
      throws IOException;

  /**
   * Merges in the fields from the readers in <code>mergeState</code>. The default implementation
   * calls {@link #mergeNormsField} for each field, filling segments with missing norms for the
   * field with zeros. Implementations can override this method for more sophisticated merging
   * (bulk-byte copying, etc).
   */
  public void merge(MergeState mergeState) throws IOException {
    for (NormsProducer normsProducer : mergeState.normsProducers) {
      if (normsProducer != null) {
        mergeState.checkAborted();
        normsProducer.checkIntegrity();
      }
    }
    for (FieldInfo mergeFieldInfo : mergeState.mergeFieldInfos) {
      if (mergeFieldInfo.hasNorms()) {
        mergeNormsField(mergeFieldInfo, mergeState);
      }
    }
  }

  /** Tracks state of one numeric sub-reader that we are merging */
  private static class NumericDocValuesSub extends DocIDMerger.Sub {

    private final NumericDocValues values;

    public NumericDocValuesSub(MergeState.DocMap docMap, NumericDocValues values) {
      super(docMap);
      this.values = values;
      assert values.docID() == -1;
    }

    @Override
    public int nextDoc() throws IOException {
      return values.nextDoc();
    }
  }

  /**
   * Merges the norms from <code>toMerge</code>.
   *
   * <p>The default implementation calls {@link #addNormsField}, passing an Iterable that merges and
   * filters deleted documents on the fly.
   */
  public void mergeNormsField(final FieldInfo mergeFieldInfo, final MergeState mergeState)
      throws IOException {

    // TODO: try to share code with default merge of DVConsumer by passing MatchAllBits ?
    addNormsField(
        mergeFieldInfo,
        new NormsProducer() {
          @Override
          public NumericDocValues getNorms(FieldInfo fieldInfo) throws IOException {
            if (fieldInfo != mergeFieldInfo) {
              throw new IllegalArgumentException("wrong fieldInfo");
            }

            List<NumericDocValuesSub> subs = new ArrayList<>();
            assert mergeState.docMaps.length == mergeState.docValuesProducers.length;
            for (int i = 0; i < mergeState.docValuesProducers.length; i++) {
              NumericDocValues norms = null;
              NormsProducer normsProducer = mergeState.normsProducers[i];
              if (normsProducer != null) {
                FieldInfo readerFieldInfo = mergeState.fieldInfos[i].fieldInfo(mergeFieldInfo.name);
                if (readerFieldInfo != null && readerFieldInfo.hasNorms()) {
                  norms = normsProducer.getNorms(readerFieldInfo);
                }
              }

              if (norms != null) {
                subs.add(new NumericDocValuesSub(mergeState.docMaps[i], norms));
              }
            }

            final DocIDMerger<NumericDocValuesSub> docIDMerger =
                DocIDMerger.of(subs, mergeState.needsIndexSort);

            return new NumericDocValues() {
              private int docID = -1;
              private NumericDocValuesSub current;

              @Override
              public int docID() {
                return docID;
              }

              @Override
              public int nextDoc() throws IOException {
                current = docIDMerger.next();
                if (current == null) {
                  docID = NO_MORE_DOCS;
                } else {
                  docID = current.mappedDocID;
                }
                return docID;
              }

              @Override
              public int advance(int target) throws IOException {
                throw new UnsupportedOperationException();
              }

              @Override
              public boolean advanceExact(int target) throws IOException {
                throw new UnsupportedOperationException();
              }

              @Override
              public long cost() {
                return 0;
              }

              @Override
              public long longValue() throws IOException {
                return current.values.longValue();
              }
            };
          }

          @Override
          public void checkIntegrity() {}

          @Override
          public void close() {}
        });
  }
}
