package org.apache.lucene.index;
   
   /*
    * 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.IOException;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import java.util.Map;
  
  import org.apache.lucene.store.Directory;
  import org.apache.lucene.store.MergeInfo;
  import org.apache.lucene.store.RateLimiter;
  import org.apache.lucene.util.FixedBitSet;
  
  /**
   * <p>Expert: a MergePolicy determines the sequence of
   * primitive merge operations.</p>
   * 
   * <p>Whenever the segments in an index have been altered by
   * {@link IndexWriter}, either the addition of a newly
   * flushed segment, addition of many segments from
   * addIndexes* calls, or a previous merge that may now need
   * to cascade, {@link IndexWriter} invokes {@link
   * #findMerges} to give the MergePolicy a chance to pick
   * merges that are now required.  This method returns a
   * {@link MergeSpecification} instance describing the set of
   * merges that should be done, or null if no merges are
   * necessary.  When IndexWriter.forceMerge is called, it calls
   * {@link #findForcedMerges(SegmentInfos,int,Map, IndexWriter)} and the MergePolicy should
   * then return the necessary merges.</p>
   *
   * <p>Note that the policy can return more than one merge at
   * a time.  In this case, if the writer is using {@link
   * SerialMergeScheduler}, the merges will be run
   * sequentially but if it is using {@link
   * ConcurrentMergeScheduler} they will be run concurrently.</p>
   * 
   * <p>The default MergePolicy is {@link
   * TieredMergePolicy}.</p>
   *
   * @lucene.experimental
   */
  public abstract class MergePolicy {
  
    /** A map of doc IDs. */
    public static abstract class DocMap {
      /** Sole constructor, typically invoked from sub-classes constructors. */
      protected DocMap() {}
  
      /** Return the new doc ID according to its old value. */
      public abstract int map(int old);
  
      /** Useful from an assert. */
      boolean isConsistent(int maxDoc) {
        final FixedBitSet targets = new FixedBitSet(maxDoc);
        for (int i = 0; i < maxDoc; ++i) {
          final int target = map(i);
          if (target < 0 || target >= maxDoc) {
            assert false : "out of range: " + target + " not in [0-" + maxDoc + "[";
            return false;
          } else if (targets.get(target)) {
            assert false : target + " is already taken (" + i + ")";
            return false;
          }
        }
        return true;
      }
    }
  
    /** OneMerge provides the information necessary to perform
     *  an individual primitive merge operation, resulting in
     *  a single new segment.  The merge spec includes the
     *  subset of segments to be merged as well as whether the
     *  new segment should use the compound file format.
     *
     * @lucene.experimental */
    public static class OneMerge {
  
      SegmentCommitInfo info;         // used by IndexWriter
      boolean registerDone;           // used by IndexWriter
      long mergeGen;                  // used by IndexWriter
      boolean isExternal;             // used by IndexWriter
      int maxNumSegments = -1;        // used by IndexWriter
 
     /** Estimated size in bytes of the merged segment. */
     public volatile long estimatedMergeBytes;       // used by IndexWriter
 
     // Sum of sizeInBytes of all SegmentInfos; set by IW.mergeInit
     volatile long totalMergeBytes;
 
     List<SegmentReader> readers;        // used by IndexWriter
 
     /** Segments to be merged. */
     public final List<SegmentCommitInfo> segments;
 
     /** A private {@link RateLimiter} for this merge, used to rate limit writes and abort. */
     public final MergeRateLimiter rateLimiter;
 
     volatile long mergeStartNS = -1;
 
     /** Total number of documents in segments to be merged, not accounting for deletions. */
     public final int totalMaxDoc;
     Throwable error;
 
     /** Sole constructor.
      * @param segments List of {@link SegmentCommitInfo}s
      *        to be merged. */
     public OneMerge(List<SegmentCommitInfo> segments) {
       if (0 == segments.size()) {
         throw new RuntimeException("segments must include at least one segment");
       }
       // clone the list, as the in list may be based off original SegmentInfos and may be modified
       this.segments = new ArrayList<>(segments);
       int count = 0;
       for(SegmentCommitInfo info : segments) {
         count += info.info.maxDoc();
       }
       totalMaxDoc = count;
 
       rateLimiter = new MergeRateLimiter(this);
     }
 
     /** Called by {@link IndexWriter} after the merge is done and all readers have been closed. */
     public void mergeFinished() throws IOException {
     }
 
     /** Expert: Get the list of readers to merge. Note that this list does not
      *  necessarily match the list of segments to merge and should only be used
      *  to feed SegmentMerger to initialize a merge. When a {@link OneMerge}
      *  reorders doc IDs, it must override {@link #getDocMap} too so that
      *  deletes that happened during the merge can be applied to the newly
      *  merged segment. */
     public List<CodecReader> getMergeReaders() throws IOException {
       if (readers == null) {
         throw new IllegalStateException("IndexWriter has not initialized readers from the segment infos yet");
       }
       final List<CodecReader> readers = new ArrayList<>(this.readers.size());
       for (SegmentReader reader : this.readers) {
         if (reader.numDocs() > 0) {
           readers.add(reader);
         }
       }
       return Collections.unmodifiableList(readers);
     }
     
     /**
      * Expert: Sets the {@link SegmentCommitInfo} of the merged segment.
      * Allows sub-classes to e.g. set diagnostics properties.
      */
     public void setMergeInfo(SegmentCommitInfo info) {
       this.info = info;
     }
 
     /**
      * Returns the {@link SegmentCommitInfo} for the merged segment,
      * or null if it hasn't been set yet.
      */
     public SegmentCommitInfo getMergeInfo() {
       return info;
     }
 
     /** Expert: If {@link #getMergeReaders()} reorders document IDs, this method
      *  must be overridden to return a mapping from the <i>natural</i> doc ID
      *  (the doc ID that would result from a natural merge) to the actual doc
      *  ID. This mapping is used to apply deletions that happened during the
      *  merge to the new segment. */
     public DocMap getDocMap(MergeState mergeState) {
       return new DocMap() {
         @Override
         public int map(int docID) {
           return docID;
         }
       };
     }
 
     /** Record that an exception occurred while executing
      *  this merge */
     synchronized void setException(Throwable error) {
       this.error = error;
     }
 
     /** Retrieve previous exception set by {@link
      *  #setException}. */
     synchronized Throwable getException() {
       return error;
     }
 
     /** Returns a readable description of the current merge
      *  state. */
     public String segString() {
       StringBuilder b = new StringBuilder();
       final int numSegments = segments.size();
       for(int i=0;i<numSegments;i++) {
         if (i > 0) {
           b.append(' ');
         }
         b.append(segments.get(i).toString());
       }
       if (info != null) {
         b.append(" into ").append(info.info.name);
       }
       if (maxNumSegments != -1) {
         b.append(" [maxNumSegments=" + maxNumSegments + "]");
       }
       if (rateLimiter.getAbort()) {
         b.append(" [ABORTED]");
       }
       return b.toString();
     }
     
     /**
      * Returns the total size in bytes of this merge. Note that this does not
      * indicate the size of the merged segment, but the
      * input total size. This is only set once the merge is
      * initialized by IndexWriter.
      */
     public long totalBytesSize() throws IOException {
       return totalMergeBytes;
     }
 
     /**
      * Returns the total number of documents that are included with this merge.
      * Note that this does not indicate the number of documents after the merge.
      * */
     public int totalNumDocs() throws IOException {
       int total = 0;
       for (SegmentCommitInfo info : segments) {
         total += info.info.maxDoc();
       }
       return total;
     }
 
     /** Return {@link MergeInfo} describing this merge. */
     public MergeInfo getStoreMergeInfo() {
       return new MergeInfo(totalMaxDoc, estimatedMergeBytes, isExternal, maxNumSegments);
     }    
   }
 
   /**
    * A MergeSpecification instance provides the information
    * necessary to perform multiple merges.  It simply
    * contains a list of {@link OneMerge} instances.
    */
 
   public static class MergeSpecification {
 
     /**
      * The subset of segments to be included in the primitive merge.
      */
 
     public final List<OneMerge> merges = new ArrayList<>();
 
     /** Sole constructor.  Use {@link
      *  #add(MergePolicy.OneMerge)} to add merges. */
     public MergeSpecification() {
     }
 
     /** Adds the provided {@link OneMerge} to this
      *  specification. */
     public void add(OneMerge merge) {
       merges.add(merge);
     }
 
     /** Returns a description of the merges in this
     *  specification. */
     public String segString(Directory dir) {
       StringBuilder b = new StringBuilder();
       b.append("MergeSpec:\n");
       final int count = merges.size();
       for(int i=0;i<count;i++) {
         b.append("  ").append(1 + i).append(": ").append(merges.get(i).segString());
       }
       return b.toString();
     }
   }
 
   /** Exception thrown if there are any problems while
    *  executing a merge. */
   public static class MergeException extends RuntimeException {
     private Directory dir;
 
     /** Create a {@code MergeException}. */
     public MergeException(String message, Directory dir) {
       super(message);
       this.dir = dir;
     }
 
     /** Create a {@code MergeException}. */
     public MergeException(Throwable exc, Directory dir) {
       super(exc);
       this.dir = dir;
     }
 
     /** Returns the {@link Directory} of the index that hit
      *  the exception. */
     public Directory getDirectory() {
       return dir;
     }
   }
 
   /** Thrown when a merge was explicity aborted because
    *  {@link IndexWriter#abortMerges} was called.  Normally
    *  this exception is privately caught and suppresed by
    *  {@link IndexWriter}. */
   public static class MergeAbortedException extends IOException {
     /** Create a {@link MergeAbortedException}. */
     public MergeAbortedException() {
       super("merge is aborted");
     }
 
     /** Create a {@link MergeAbortedException} with a
      *  specified message. */
     public MergeAbortedException(String message) {
       super(message);
     }
   }
   
   /**
    * Default ratio for compound file system usage. Set to <tt>1.0</tt>, always use 
    * compound file system.
    */
   protected static final double DEFAULT_NO_CFS_RATIO = 1.0;
 
   /**
    * Default max segment size in order to use compound file system. Set to {@link Long#MAX_VALUE}.
    */
   protected static final long DEFAULT_MAX_CFS_SEGMENT_SIZE = Long.MAX_VALUE;
 
   /** If the size of the merge segment exceeds this ratio of
    *  the total index size then it will remain in
    *  non-compound format */
   protected double noCFSRatio = DEFAULT_NO_CFS_RATIO;
   
   /** If the size of the merged segment exceeds
    *  this value then it will not use compound file format. */
   protected long maxCFSSegmentSize = DEFAULT_MAX_CFS_SEGMENT_SIZE;
 
   /**
    * Creates a new merge policy instance.
    */
   public MergePolicy() {
     this(DEFAULT_NO_CFS_RATIO, DEFAULT_MAX_CFS_SEGMENT_SIZE);
   }
   
   /**
    * Creates a new merge policy instance with default settings for noCFSRatio
    * and maxCFSSegmentSize. This ctor should be used by subclasses using different
    * defaults than the {@link MergePolicy}
    */
   protected MergePolicy(double defaultNoCFSRatio, long defaultMaxCFSSegmentSize) {
     this.noCFSRatio = defaultNoCFSRatio;
     this.maxCFSSegmentSize = defaultMaxCFSSegmentSize;
   }
 
   /**
    * Determine what set of merge operations are now necessary on the index.
    * {@link IndexWriter} calls this whenever there is a change to the segments.
    * This call is always synchronized on the {@link IndexWriter} instance so
    * only one thread at a time will call this method.
    * @param mergeTrigger the event that triggered the merge
    * @param segmentInfos
    *          the total set of segments in the index
    * @param writer the IndexWriter to find the merges on
    */
   public abstract MergeSpecification findMerges(MergeTrigger mergeTrigger, SegmentInfos segmentInfos, IndexWriter writer)
       throws IOException;
 
   /**
    * Determine what set of merge operations is necessary in
    * order to merge to {@code <=} the specified segment count. {@link IndexWriter} calls this when its
    * {@link IndexWriter#forceMerge} method is called. This call is always
    * synchronized on the {@link IndexWriter} instance so only one thread at a
    * time will call this method.
    * 
    * @param segmentInfos
    *          the total set of segments in the index
    * @param maxSegmentCount
    *          requested maximum number of segments in the index (currently this
    *          is always 1)
    * @param segmentsToMerge
    *          contains the specific SegmentInfo instances that must be merged
    *          away. This may be a subset of all
    *          SegmentInfos.  If the value is True for a
    *          given SegmentInfo, that means this segment was
    *          an original segment present in the
    *          to-be-merged index; else, it was a segment
    *          produced by a cascaded merge.
    * @param writer the IndexWriter to find the merges on
    */
   public abstract MergeSpecification findForcedMerges(
           SegmentInfos segmentInfos, int maxSegmentCount, Map<SegmentCommitInfo,Boolean> segmentsToMerge, IndexWriter writer)
       throws IOException;
 
   /**
    * Determine what set of merge operations is necessary in order to expunge all
    * deletes from the index.
    * 
    * @param segmentInfos
    *          the total set of segments in the index
    * @param writer the IndexWriter to find the merges on
    */
   public abstract MergeSpecification findForcedDeletesMerges(
       SegmentInfos segmentInfos, IndexWriter writer) throws IOException;
 
   /**
    * Returns true if a new segment (regardless of its origin) should use the
    * compound file format. The default implementation returns <code>true</code>
    * iff the size of the given mergedInfo is less or equal to
    * {@link #getMaxCFSSegmentSizeMB()} and the size is less or equal to the
    * TotalIndexSize * {@link #getNoCFSRatio()} otherwise <code>false</code>.
    */
   public boolean useCompoundFile(SegmentInfos infos, SegmentCommitInfo mergedInfo, IndexWriter writer) throws IOException {
     if (getNoCFSRatio() == 0.0) {
       return false;
     }
     long mergedInfoSize = size(mergedInfo, writer);
     if (mergedInfoSize > maxCFSSegmentSize) {
       return false;
     }
     if (getNoCFSRatio() >= 1.0) {
       return true;
     }
     long totalSize = 0;
     for (SegmentCommitInfo info : infos) {
       totalSize += size(info, writer);
     }
     return mergedInfoSize <= getNoCFSRatio() * totalSize;
   }
   
   /** Return the byte size of the provided {@link
    *  SegmentCommitInfo}, pro-rated by percentage of
    *  non-deleted documents is set. */
   protected long size(SegmentCommitInfo info, IndexWriter writer) throws IOException {
     long byteSize = info.sizeInBytes();
     int delCount = writer.numDeletedDocs(info);
     double delRatio = info.info.maxDoc() <= 0 ? 0.0f : (float) delCount / (float) info.info.maxDoc();
     assert delRatio <= 1.0;
     return (info.info.maxDoc() <= 0 ? byteSize : (long) (byteSize * (1.0 - delRatio)));
   }
   
   /** Returns true if this single info is already fully merged (has no
    *  pending deletes, is in the same dir as the
    *  writer, and matches the current compound file setting */
   protected final boolean isMerged(SegmentInfos infos, SegmentCommitInfo info, IndexWriter writer) throws IOException {
     assert writer != null;
     boolean hasDeletions = writer.numDeletedDocs(info) > 0;
     return !hasDeletions &&
       info.info.dir == writer.getDirectory() &&
       useCompoundFile(infos, info, writer) == info.info.getUseCompoundFile();
   }
   
   /** Returns current {@code noCFSRatio}.
    *
    *  @see #setNoCFSRatio */
   public final double getNoCFSRatio() {
     return noCFSRatio;
   }
 
   /** If a merged segment will be more than this percentage
    *  of the total size of the index, leave the segment as
    *  non-compound file even if compound file is enabled.
    *  Set to 1.0 to always use CFS regardless of merge
    *  size. */
   public final void setNoCFSRatio(double noCFSRatio) {
     if (noCFSRatio < 0.0 || noCFSRatio > 1.0) {
       throw new IllegalArgumentException("noCFSRatio must be 0.0 to 1.0 inclusive; got " + noCFSRatio);
     }
     this.noCFSRatio = noCFSRatio;
   }
 
   /** Returns the largest size allowed for a compound file segment */
   public final double getMaxCFSSegmentSizeMB() {
     return maxCFSSegmentSize/1024/1024.;
   }
 
   /** If a merged segment will be more than this value,
    *  leave the segment as
    *  non-compound file even if compound file is enabled.
    *  Set this to Double.POSITIVE_INFINITY (default) and noCFSRatio to 1.0
    *  to always use CFS regardless of merge size. */
   public final void setMaxCFSSegmentSizeMB(double v) {
     if (v < 0.0) {
       throw new IllegalArgumentException("maxCFSSegmentSizeMB must be >=0 (got " + v + ")");
     }
     v *= 1024 * 1024;
     this.maxCFSSegmentSize = v > Long.MAX_VALUE ? Long.MAX_VALUE : (long) v;
   }
 }