/*
    * 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.util;
  
  import java.io.IOException;
  import java.lang.reflect.Constructor;
  import java.util.zip.Checksum;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  
  /**
   * Checksum types. The Checksum type is a one byte number
   * that stores a representation of the checksum algorithm
   * used to encode a hfile. The ordinal of these cannot
   * change or else you risk breaking all existing HFiles out there.
   */
  @InterfaceAudience.Private
  public enum ChecksumType {
  
    NULL((byte)0) {
      @Override
      public String getName() {
        return "NULL";
      }
      @Override
      public void initialize() {
        // do nothing
      }
      @Override
      public Checksum getChecksumObject() throws IOException {
        return null; // checksums not used
      }
    },
  
    CRC32((byte)1) {
      private transient Constructor<?> ctor;
  
      @Override
      public String getName() {
        return "CRC32";
      }
  
      @Override
      public void initialize() {
        final String PURECRC32 = "org.apache.hadoop.util.PureJavaCrc32";
        final String JDKCRC = "java.util.zip.CRC32";
        LOG = LogFactory.getLog(ChecksumType.class);
  
        // check if hadoop library is available
        try {
          ctor = ChecksumFactory.newConstructor(PURECRC32);
          LOG.debug(PURECRC32 + " available");
        } catch (Exception e) {
          LOG.trace(PURECRC32 + " not available.");
        }
        try {
          // The default checksum class name is java.util.zip.CRC32.
          // This is available on all JVMs.
          if (ctor == null) {
            ctor = ChecksumFactory.newConstructor(JDKCRC);
            LOG.debug(JDKCRC + " available");
          }
        } catch (Exception e) {
          LOG.trace(JDKCRC + " not available.");
        }
      }
  
      @Override
      public Checksum getChecksumObject() throws IOException {
        if (ctor == null) {
          throw new IOException("Bad constructor for " + getName());
        }
        try {
          return (Checksum)ctor.newInstance();
        } catch (Exception e) {
          throw new IOException(e);
        }
      }
    },
  
    CRC32C((byte)2) {
     private transient Constructor<?> ctor;
 
     @Override
     public String getName() {
       return "CRC32C";
     }
 
     @Override
     public void initialize() {
       final String PURECRC32C = "org.apache.hadoop.util.PureJavaCrc32C";
       LOG = LogFactory.getLog(ChecksumType.class);
       try {
         ctor = ChecksumFactory.newConstructor(PURECRC32C);
         LOG.debug(PURECRC32C + " available");
       } catch (Exception e) {
         LOG.trace(PURECRC32C + " not available.");
       }
     }
 
     @Override
     public Checksum getChecksumObject() throws IOException {
       if (ctor == null) {
         throw new IOException("Bad constructor for " + getName());
       }
       try {
         return (Checksum)ctor.newInstance();
       } catch (Exception e) {
         throw new IOException(e);
       }
     }
   };
 
   private final byte code;
   protected Log LOG;
 
   /** initializes the relevant checksum class object */
   abstract void initialize();
 
   /** returns the name of this checksum type */
   public abstract String getName();
 
   private ChecksumType(final byte c) {
     this.code = c;
     initialize();
   }
 
   /** returns a object that can be used to generate/validate checksums */
   public abstract Checksum getChecksumObject() throws IOException;
 
   public byte getCode() {
     return this.code;
   }
 
   /**
    * Cannot rely on enum ordinals . They change if item is removed or moved.
    * Do our own codes.
    * @param b
    * @return Type associated with passed code.
    */
   public static ChecksumType codeToType(final byte b) {
     for (ChecksumType t : ChecksumType.values()) {
       if (t.getCode() == b) {
         return t;
       }
     }
     throw new RuntimeException("Unknown checksum type code " + b);
   }
 
   /**
    * Map a checksum name to a specific type.
    * Do our own names.
    * @param name
    * @return Type associated with passed code.
    */
   public static ChecksumType nameToType(final String name) {
     for (ChecksumType t : ChecksumType.values()) {
       if (t.getName().equals(name)) {
         return t;
       }
     }
     throw new RuntimeException("Unknown checksum type name " + name);
   }
 }