package org.apache.lucene.codecs.perfield;

/*
 * 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.
 */

import java.io.Closeable;
import java.io.IOException;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.ServiceLoader; // javadocs
import java.util.TreeMap;

import org.apache.lucene.codecs.FieldsConsumer;
import org.apache.lucene.codecs.FieldsProducer;
import org.apache.lucene.codecs.PostingsFormat;
import org.apache.lucene.codecs.TermsConsumer;
import org.apache.lucene.index.FieldInfo;
import org.apache.lucene.index.SegmentReadState;
import org.apache.lucene.index.SegmentWriteState;
import org.apache.lucene.index.Terms;
import org.apache.lucene.util.IOUtils;
import org.apache.lucene.util.RamUsageEstimator;

/**
 * Enables per field postings support.
 * <p>
 * Note, when extending this class, the name ({@link #getName}) is 
 * written into the index. In order for the field to be read, the
 * name must resolve to your implementation via {@link #forName(String)}.
 * This method uses Java's 
 * {@link ServiceLoader Service Provider Interface} to resolve format names.
 * <p>
 * Files written by each posting format have an additional suffix containing the 
 * format name. For example, in a per-field configuration instead of <tt>_1.prx</tt> 
 * filenames would look like <tt>_1_Lucene40_0.prx</tt>.
 * @see ServiceLoader
 * @lucene.experimental
 */

public abstract class PerFieldPostingsFormat extends PostingsFormat {
  /** Name of this {@link PostingsFormat}. */
  public static final String PER_FIELD_NAME = "PerField40";

  /** {@link FieldInfo} attribute name used to store the
   *  format name for each field. */
  public static final String PER_FIELD_FORMAT_KEY = PerFieldPostingsFormat.class.getSimpleName() + ".format";

  /** {@link FieldInfo} attribute name used to store the
   *  segment suffix name for each field. */
  public static final String PER_FIELD_SUFFIX_KEY = PerFieldPostingsFormat.class.getSimpleName() + ".suffix";

  
  /** Sole constructor. */
  public PerFieldPostingsFormat() {
    super(PER_FIELD_NAME);
  }

  @Override
  public final FieldsConsumer fieldsConsumer(SegmentWriteState state)
      throws IOException {
    return new FieldsWriter(state);
  }
  
  static class FieldsConsumerAndSuffix implements Closeable {
    FieldsConsumer consumer;
    int suffix;
    
    @Override
    public void close() throws IOException {
      consumer.close();
    }
  }
    
  private class FieldsWriter extends FieldsConsumer {

    private final Map<PostingsFormat,FieldsConsumerAndSuffix> formats = new HashMap<>();
    private final Map<String,Integer> suffixes = new HashMap<>();
    
    private final SegmentWriteState segmentWriteState;

    public FieldsWriter(SegmentWriteState state) {
      segmentWriteState = state;
    }

    @Override
    public TermsConsumer addField(FieldInfo field) throws IOException {
      final PostingsFormat format = getPostingsFormatForField(field.name);
      if (format == null) {
        throw new IllegalStateException("invalid null PostingsFormat for field=\"" + field.name + "\"");
      }
      final String formatName = format.getName();
      
      String previousValue = field.putAttribute(PER_FIELD_FORMAT_KEY, formatName);
      assert previousValue == null;
      
      Integer suffix;
      
      FieldsConsumerAndSuffix consumer = formats.get(format);
      if (consumer == null) {
        // First time we are seeing this format; create a new instance
        
        // bump the suffix
        suffix = suffixes.get(formatName);
        if (suffix == null) {
          suffix = 0;
        } else {
          suffix = suffix + 1;
        }
        suffixes.put(formatName, suffix);
        
        final String segmentSuffix = getFullSegmentSuffix(field.name,
                                                          segmentWriteState.segmentSuffix,
                                                          getSuffix(formatName, Integer.toString(suffix)));
        consumer = new FieldsConsumerAndSuffix();
        consumer.consumer = format.fieldsConsumer(new SegmentWriteState(segmentWriteState, segmentSuffix));
        consumer.suffix = suffix;
        formats.put(format, consumer);
      } else {
        // we've already seen this format, so just grab its suffix
        assert suffixes.containsKey(formatName);
        suffix = consumer.suffix;
      }
      
      previousValue = field.putAttribute(PER_FIELD_SUFFIX_KEY, Integer.toString(suffix));
      assert previousValue == null;

      // TODO: we should only provide the "slice" of FIS
      // that this PF actually sees ... then stuff like
      // .hasProx could work correctly?
      // NOTE: .hasProx is already broken in the same way for the non-perfield case,
      // if there is a fieldinfo with prox that has no postings, you get a 0 byte file.
      return consumer.consumer.addField(field);
    }

    @Override
    public void close() throws IOException {
      // Close all subs
      IOUtils.close(formats.values());
    }
  }
  
  static String getSuffix(String formatName, String suffix) {
    return formatName + "_" + suffix;
  }

  static String getFullSegmentSuffix(String fieldName, String outerSegmentSuffix, String segmentSuffix) {
    if (outerSegmentSuffix.length() == 0) {
      return segmentSuffix;
    } else {
      // TODO: support embedding; I think it should work but
      // we need a test confirm to confirm
      // return outerSegmentSuffix + "_" + segmentSuffix;
      throw new IllegalStateException("cannot embed PerFieldPostingsFormat inside itself (field \"" + fieldName + "\" returned PerFieldPostingsFormat)");
    }
  }

  private class FieldsReader extends FieldsProducer {

    private final Map<String,FieldsProducer> fields = new TreeMap<>();
    private final Map<String,FieldsProducer> formats = new HashMap<>();

    public FieldsReader(final SegmentReadState readState) throws IOException {

      // Read _X.per and init each format:
      boolean success = false;
      try {
        // Read field name -> format name
        for (FieldInfo fi : readState.fieldInfos) {
          if (fi.isIndexed()) {
            final String fieldName = fi.name;
            final String formatName = fi.getAttribute(PER_FIELD_FORMAT_KEY);
            if (formatName != null) {
              // null formatName means the field is in fieldInfos, but has no postings!
              final String suffix = fi.getAttribute(PER_FIELD_SUFFIX_KEY);
              assert suffix != null;
              PostingsFormat format = PostingsFormat.forName(formatName);
              String segmentSuffix = getSuffix(formatName, suffix);
              if (!formats.containsKey(segmentSuffix)) {
                formats.put(segmentSuffix, format.fieldsProducer(new SegmentReadState(readState, segmentSuffix)));
              }
              fields.put(fieldName, formats.get(segmentSuffix));
            }
          }
        }
        success = true;
      } finally {
        if (!success) {
          IOUtils.closeWhileHandlingException(formats.values());
        }
      }
    }

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

    @Override
    public Terms terms(String field) throws IOException {
      FieldsProducer fieldsProducer = fields.get(field);
      return fieldsProducer == null ? null : fieldsProducer.terms(field);
    }
    
    @Override
    public int size() {
      return fields.size();
    }

    @Override
    public void close() throws IOException {
      IOUtils.close(formats.values());
    }

    @Override
    public long ramBytesUsed() {
      long sizeInBytes = 0;
      for(Map.Entry<String,FieldsProducer> entry: formats.entrySet()) {
        sizeInBytes += entry.getKey().length() * RamUsageEstimator.NUM_BYTES_CHAR;
        sizeInBytes += entry.getValue().ramBytesUsed();
      }
      return sizeInBytes;
    }

    @Override
    public void checkIntegrity() throws IOException {
      for (FieldsProducer producer : formats.values()) {
        producer.checkIntegrity();
      }
    }
  }

  @Override
  public final FieldsProducer fieldsProducer(SegmentReadState state)
      throws IOException {
    return new FieldsReader(state);
  }

  /** 
   * Returns the postings format that should be used for writing 
   * new segments of <code>field</code>.
   * <p>
   * The field to format mapping is written to the index, so
   * this method is only invoked when writing, not when reading. */
  public abstract PostingsFormat getPostingsFormatForField(String field);
}
