/*
 * 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.search.join;

import java.io.IOException;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.search.DocIdSetIterator;
import org.apache.lucene.util.BitSet;
import org.apache.lucene.util.BitSetIterator;
import org.apache.lucene.util.Bits;

/** Utility class to check a block join index. */
public class CheckJoinIndex {

  private CheckJoinIndex() {}

  /**
   * Check that the given index is good to use for block joins.
   *
   * @throws IllegalStateException if the index does not have an appropriate structure
   */
  public static void check(IndexReader reader, BitSetProducer parentsFilter) throws IOException {
    for (LeafReaderContext context : reader.leaves()) {
      if (context.reader().maxDoc() == 0) {
        continue;
      }
      final BitSet parents = parentsFilter.getBitSet(context);
      if (parents == null || parents.cardinality() == 0) {
        throw new IllegalStateException(
            "Every segment should have at least one parent, but "
                + context.reader()
                + " does not have any");
      }
      if (parents.get(context.reader().maxDoc() - 1) == false) {
        throw new IllegalStateException(
            "The last document of a segment must always be a parent, but "
                + context.reader()
                + " has a child as a last doc");
      }
      final Bits liveDocs = context.reader().getLiveDocs();
      if (liveDocs != null) {
        int prevParentDoc = -1;
        DocIdSetIterator it = new BitSetIterator(parents, 0L);
        for (int parentDoc = it.nextDoc();
            parentDoc != DocIdSetIterator.NO_MORE_DOCS;
            parentDoc = it.nextDoc()) {
          final boolean parentIsLive = liveDocs.get(parentDoc);
          for (int child = prevParentDoc + 1; child != parentDoc; child++) {
            final boolean childIsLive = liveDocs.get(child);
            if (parentIsLive != childIsLive) {
              if (parentIsLive) {
                throw new IllegalStateException(
                    "Parent doc "
                        + parentDoc
                        + " of segment "
                        + context.reader()
                        + " is live but has a deleted child document "
                        + child);
              } else {
                throw new IllegalStateException(
                    "Parent doc "
                        + parentDoc
                        + " of segment "
                        + context.reader()
                        + " is deleted but has a live child document "
                        + child);
              }
            }
          }
          prevParentDoc = parentDoc;
        }
      }
    }
  }
}
