/**
    *
    * 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.hadoop.hbase.io;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.fs.FileSystem;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.KeyValue;
  import org.apache.hadoop.hbase.client.Scan;
  import org.apache.hadoop.hbase.io.hfile.CacheConfig;
  import org.apache.hadoop.hbase.io.hfile.HFileScanner;
  import org.apache.hadoop.hbase.regionserver.StoreFile;
  import org.apache.hadoop.hbase.util.Bytes;
  
  /**
   * A facade for a {@link org.apache.hadoop.hbase.io.hfile.HFile.Reader} that serves up
   * either the top or bottom half of a HFile where 'bottom' is the first half
   * of the file containing the keys that sort lowest and 'top' is the second half
   * of the file with keys that sort greater than those of the bottom half.
   * The top includes the split files midkey, of the key that follows if it does
   * not exist in the file.
   *
   * <p>This type works in tandem with the {@link Reference} type.  This class
   * is used reading while Reference is used writing.
   *
   * <p>This file is not splitable.  Calls to {@link #midkey()} return null.
   */
  @InterfaceAudience.Private
  public class HalfStoreFileReader extends StoreFile.Reader {
    private static final Log LOG = LogFactory.getLog(HalfStoreFileReader.class);
    final boolean top;
    // This is the key we split around.  Its the first possible entry on a row:
    // i.e. empty column and a timestamp of LATEST_TIMESTAMP.
    protected final byte [] splitkey;
  
    protected final Cell splitCell;
  
    private Cell firstKey = null;
  
    private boolean firstKeySeeked = false;
  
    /**
     * Creates a half file reader for a normal hfile.
     * @param fs fileystem to read from
     * @param p path to hfile
     * @param cacheConf
     * @param r original reference file (contains top or bottom)
     * @param conf Configuration
     * @throws IOException
     */
    public HalfStoreFileReader(final FileSystem fs, final Path p,
        final CacheConfig cacheConf, final Reference r, final Configuration conf)
        throws IOException {
      super(fs, p, cacheConf, conf);
      // This is not actual midkey for this half-file; its just border
      // around which we split top and bottom.  Have to look in files to find
      // actual last and first keys for bottom and top halves.  Half-files don't
      // have an actual midkey themselves. No midkey is how we indicate file is
      // not splittable.
      this.splitkey = r.getSplitKey();
      this.splitCell = new KeyValue.KeyOnlyKeyValue(this.splitkey, 0, this.splitkey.length);
      // Is it top or bottom half?
      this.top = Reference.isTopFileRegion(r.getFileRegion());
    }
  
    /**
     * Creates a half file reader for a hfile referred to by an hfilelink.
     * @param fs fileystem to read from
     * @param p path to hfile
     * @param in {@link FSDataInputStreamWrapper}
     * @param size Full size of the hfile file
     * @param cacheConf
     * @param r original reference file (contains top or bottom)
     * @param conf Configuration
     * @throws IOException
    */
   public HalfStoreFileReader(final FileSystem fs, final Path p, final FSDataInputStreamWrapper in,
       long size, final CacheConfig cacheConf,  final Reference r, final Configuration conf)
       throws IOException {
     super(fs, p, in, size, cacheConf, conf);
     // This is not actual midkey for this half-file; its just border
     // around which we split top and bottom.  Have to look in files to find
     // actual last and first keys for bottom and top halves.  Half-files don't
     // have an actual midkey themselves. No midkey is how we indicate file is
     // not splittable.
     this.splitkey = r.getSplitKey();
     this.splitCell = new KeyValue.KeyOnlyKeyValue(this.splitkey, 0, this.splitkey.length);
     // Is it top or bottom half?
     this.top = Reference.isTopFileRegion(r.getFileRegion());
   }
 
   protected boolean isTop() {
     return this.top;
   }
 
   @Override
   public HFileScanner getScanner(final boolean cacheBlocks,
       final boolean pread, final boolean isCompaction) {
     final HFileScanner s = super.getScanner(cacheBlocks, pread, isCompaction);
     return new HFileScanner() {
       final HFileScanner delegate = s;
       public boolean atEnd = false;
 
       public Cell getKey() {
         if (atEnd) return null;
         return delegate.getKey();
       }
 
       public String getKeyString() {
         if (atEnd) return null;
 
         return delegate.getKeyString();
       }
 
       public ByteBuffer getValue() {
         if (atEnd) return null;
 
         return delegate.getValue();
       }
 
       public String getValueString() {
         if (atEnd) return null;
 
         return delegate.getValueString();
       }
 
       public Cell getCell() {
         if (atEnd) return null;
 
         return delegate.getCell();
       }
 
       public boolean next() throws IOException {
         if (atEnd) return false;
 
         boolean b = delegate.next();
         if (!b) {
           return b;
         }
         // constrain the bottom.
         if (!top) {
           if (getComparator().compare(splitCell, getKey()) <= 0) {
             atEnd = true;
             return false;
           }
         }
         return true;
       }
 
       @Override
       public boolean seekTo() throws IOException {
         if (top) {
           int r = this.delegate.seekTo(splitCell);
           if (r == HConstants.INDEX_KEY_MAGIC) {
             return true;
           }
           if (r < 0) {
             // midkey is < first key in file
             return this.delegate.seekTo();
           }
           if (r > 0) {
             return this.delegate.next();
           }
           return true;
         }
 
         boolean b = delegate.seekTo();
         if (!b) {
           return b;
         }
         // Check key.
         return (this.delegate.getReader().getComparator().compare(splitCell, getKey())) > 0;
       }
 
       public org.apache.hadoop.hbase.io.hfile.HFile.Reader getReader() {
         return this.delegate.getReader();
       }
 
       public boolean isSeeked() {
         return this.delegate.isSeeked();
       }
 
       @Override
       public int seekTo(Cell key) throws IOException {
         if (top) {
           if (getComparator().compareKeyIgnoresMvcc(key, splitCell) < 0) {
             return -1;
           }
         } else {
           if (getComparator().compareKeyIgnoresMvcc(key, splitCell) >= 0) {
             // we would place the scanner in the second half.
             // it might be an error to return false here ever...
             boolean res = delegate.seekBefore(splitCell);
             if (!res) {
               throw new IOException(
                   "Seeking for a key in bottom of file, but key exists in top of file, " +
                   "failed on seekBefore(midkey)");
             }
             return 1;
           }
         }
         return delegate.seekTo(key);
       }
 
       @Override
       public int reseekTo(Cell key) throws IOException {
         // This function is identical to the corresponding seekTo function
         // except
         // that we call reseekTo (and not seekTo) on the delegate.
         if (top) {
           if (getComparator().compareKeyIgnoresMvcc(key, splitCell) < 0) {
             return -1;
           }
         } else {
           if (getComparator().compareKeyIgnoresMvcc(key, splitCell) >= 0) {
             // we would place the scanner in the second half.
             // it might be an error to return false here ever...
             boolean res = delegate.seekBefore(splitCell);
             if (!res) {
               throw new IOException("Seeking for a key in bottom of file, but"
                   + " key exists in top of file, failed on seekBefore(midkey)");
             }
             return 1;
           }
         }
         if (atEnd) {
           // skip the 'reseek' and just return 1.
           return 1;
         }
         return delegate.reseekTo(key);
       }
 
       @Override
       public boolean seekBefore(Cell key) throws IOException {
         if (top) {
           Cell fk = getFirstKey();
           if (getComparator().compareKeyIgnoresMvcc(key, fk) <= 0) {
             return false;
           }
         } else {
           // The equals sign isn't strictly necessary just here to be consistent
           // with seekTo
           if (getComparator().compareKeyIgnoresMvcc(key, splitCell) >= 0) {
             boolean ret = this.delegate.seekBefore(splitCell);
             if (ret) {
               atEnd = false;
             }
             return ret;
           }
         }
         boolean ret = this.delegate.seekBefore(key);
         if (ret) {
           atEnd = false;
         }
         return ret;
       }
 
       @Override
       public Cell getNextIndexedKey() {
         return null;
       }
 
       @Override
       public void close() {
         this.delegate.close();
       }
 
       @Override
       public void shipped() throws IOException {
         this.delegate.shipped();
       }
     };
   }
   
   @Override
   public boolean passesKeyRangeFilter(Scan scan) {
     return true;
   }
   
   @Override
   public Cell getLastKey() {
     if (top) {
       return super.getLastKey();
     }
     // Get a scanner that caches the block and that uses pread.
     HFileScanner scanner = getScanner(true, true);
     try {
       if (scanner.seekBefore(this.splitCell)) {
         return scanner.getKey();
       }
     } catch (IOException e) {
       LOG.warn("Failed seekBefore " + Bytes.toStringBinary(this.splitkey), e);
     }
     return null;
   }
 
   @Override
   public Cell midkey() throws IOException {
     // Returns null to indicate file is not splitable.
     return null;
   }
 
   @Override
   public Cell getFirstKey() {
     if (!firstKeySeeked) {
       HFileScanner scanner = getScanner(true, true, false);
       try {
         if (scanner.seekTo()) {
           this.firstKey = scanner.getKey();
         }
         firstKeySeeked = true;
       } catch (IOException e) {
         LOG.warn("Failed seekTo first KV in the file", e);
       }
     }
     return this.firstKey;
   }
 
   @Override
   public long getEntries() {
     // Estimate the number of entries as half the original file; this may be wildly inaccurate.
     return super.getEntries() / 2;
   }
 
   @Override
   public long getFilterEntries() {
     // Estimate the number of entries as half the original file; this may be wildly inaccurate.
     return super.getFilterEntries() / 2;
   }
 }