/*
 * 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.suggest.document;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.apache.lucene.codecs.CodecUtil;
import org.apache.lucene.codecs.FieldsProducer;
import org.apache.lucene.codecs.PostingsFormat;
import org.apache.lucene.index.FieldInfo;
import org.apache.lucene.index.IndexFileNames;
import org.apache.lucene.index.SegmentReadState;
import org.apache.lucene.index.Terms;
import org.apache.lucene.search.suggest.document.CompletionPostingsFormat.FSTLoadMode;
import org.apache.lucene.store.ChecksumIndexInput;
import org.apache.lucene.store.IndexInput;
import org.apache.lucene.util.Accountable;
import org.apache.lucene.util.Accountables;
import org.apache.lucene.util.IOUtils;

import static org.apache.lucene.search.suggest.document.CompletionPostingsFormat.CODEC_NAME;
import static org.apache.lucene.search.suggest.document.CompletionPostingsFormat.COMPLETION_CODEC_VERSION;
import static org.apache.lucene.search.suggest.document.CompletionPostingsFormat.COMPLETION_VERSION_CURRENT;
import static org.apache.lucene.search.suggest.document.CompletionPostingsFormat.DICT_EXTENSION;
import static org.apache.lucene.search.suggest.document.CompletionPostingsFormat.INDEX_EXTENSION;

 Completion index (.cmp) is opened and read at instantiation to read in SuggestField numbers and their FST offsets in the Completion dictionary (.lkp). 
 Completion dictionary (.lkp) is opened at instantiation and a field's FST is loaded into memory the first time it is requested via terms(String). 

NOTE: Only the footer is validated for Completion dictionary (.lkp) and not the checksum due
to random access pattern and checksum validation being too costly at instantiation

/**
 * <p>
 * Completion index (.cmp) is opened and read at instantiation to read in {@link SuggestField}
 * numbers and their FST offsets in the Completion dictionary (.lkp).
 * </p>
 * <p>
 * Completion dictionary (.lkp) is opened at instantiation and a field's FST is loaded
 * into memory the first time it is requested via {@link #terms(String)}.
 * </p>
 * <p>
 * NOTE: Only the footer is validated for Completion dictionary (.lkp) and not the checksum due
 * to random access pattern and checksum validation being too costly at instantiation
 * </p>
 *
 */
final class CompletionFieldsProducer extends FieldsProducer {

  private FieldsProducer delegateFieldsProducer;
  private Map<String, CompletionsTermsReader> readers;
  private IndexInput dictIn;

  // copy ctr for merge instance
  private CompletionFieldsProducer(FieldsProducer delegateFieldsProducer, Map<String, CompletionsTermsReader> readers) {
    this.delegateFieldsProducer = delegateFieldsProducer;
    this.readers = readers;
  }

  CompletionFieldsProducer(SegmentReadState state, FSTLoadMode fstLoadMode) throws IOException {
    String indexFile = IndexFileNames.segmentFileName(state.segmentInfo.name, state.segmentSuffix, INDEX_EXTENSION);
    delegateFieldsProducer = null;
    boolean success = false;

    try (ChecksumIndexInput index = state.directory.openChecksumInput(indexFile, state.context)) {
      // open up dict file containing all fsts
      String dictFile = IndexFileNames.segmentFileName(state.segmentInfo.name, state.segmentSuffix, DICT_EXTENSION);
      dictIn = state.directory.openInput(dictFile, state.context);
      CodecUtil.checkIndexHeader(dictIn, CODEC_NAME, COMPLETION_CODEC_VERSION, COMPLETION_VERSION_CURRENT, state.segmentInfo.getId(), state.segmentSuffix);
      // just validate the footer for the dictIn
      CodecUtil.retrieveChecksum(dictIn);

      // open up index file (fieldNumber, offset)
      CodecUtil.checkIndexHeader(index, CODEC_NAME, COMPLETION_CODEC_VERSION, COMPLETION_VERSION_CURRENT, state.segmentInfo.getId(), state.segmentSuffix);
      // load delegate PF
      PostingsFormat delegatePostingsFormat = PostingsFormat.forName(index.readString());
      delegateFieldsProducer = delegatePostingsFormat.fieldsProducer(state);

      // read suggest field numbers and their offsets in the terms file from index
      int numFields = index.readVInt();
      readers = new HashMap<>(numFields);
      for (int i = 0; i < numFields; i++) {
        int fieldNumber = index.readVInt();
        long offset = index.readVLong();
        long minWeight = index.readVLong();
        long maxWeight = index.readVLong();
        byte type = index.readByte();
        FieldInfo fieldInfo = state.fieldInfos.fieldInfo(fieldNumber);
        // we don't load the FST yet
        readers.put(fieldInfo.name, new CompletionsTermsReader(dictIn, offset, minWeight, maxWeight, type, fstLoadMode));
      }
      CodecUtil.checkFooter(index);
      success = true;
    } finally {
      if (success == false) {
        IOUtils.closeWhileHandlingException(delegateFieldsProducer, dictIn);
      }
    }
  }

  @Override
  public void close() throws IOException {
    boolean success = false;
    try {
      delegateFieldsProducer.close();
      IOUtils.close(dictIn);
      success = true;
    } finally {
      if (success == false) {
        IOUtils.closeWhileHandlingException(delegateFieldsProducer, dictIn);
      }
    }
  }

  @Override
  public void checkIntegrity() throws IOException {
    delegateFieldsProducer.checkIntegrity();
    // TODO: checkIntegrity should checksum the dictionary and index
  }

  @Override
  public FieldsProducer getMergeInstance() {
    return new CompletionFieldsProducer(delegateFieldsProducer, readers);
  }

  @Override
  public long ramBytesUsed() {
    long ramBytesUsed = delegateFieldsProducer.ramBytesUsed();
    for (CompletionsTermsReader reader : readers.values()) {
      ramBytesUsed += reader.ramBytesUsed();
    }
    return ramBytesUsed;
  }

  @Override
  public Collection<Accountable> getChildResources() {
    List<Accountable> accountableList = new ArrayList<>();
    for (Map.Entry<String, CompletionsTermsReader> readerEntry : readers.entrySet()) {
      accountableList.add(Accountables.namedAccountable(readerEntry.getKey(), readerEntry.getValue()));
    }
    return Collections.unmodifiableCollection(accountableList);
  }

  @Override
  public Iterator<String> iterator() {
    return readers.keySet().iterator();
  }

  @Override
  public Terms terms(String field) throws IOException {
    Terms terms = delegateFieldsProducer.terms(field) ;
    if (terms == null) {
      return null;
    }
    return new CompletionTerms(terms, readers.get(field));
  }

  @Override
  public int size() {
    return readers.size();
  }

}