/*
    * 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.maven.buildcache.hash;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.nio.channels.FileChannel;
  import java.nio.file.Files;
  import java.nio.file.Path;
  
  import net.openhft.hashing.LongHashFunction;
  
  import static java.nio.channels.FileChannel.MapMode.READ_ONLY;
  import static java.nio.file.StandardOpenOption.READ;
  
  /**
   * Zero-Allocation-Hash based factory
   */
  public class Zah implements Hash.Factory {
  
      public enum MemoryPolicy {
          Standard,
          MemoryMappedBuffers
      }
  
      private final String name;
      private final LongHashFunction hash;
      private final MemoryPolicy memoryPolicy;
  
      public Zah(String name, LongHashFunction hash, MemoryPolicy memoryPolicy) {
          this.name = name;
          this.hash = hash;
          this.memoryPolicy = memoryPolicy != null ? memoryPolicy : MemoryPolicy.Standard;
      }
  
      @Override
      public String getAlgorithm() {
          return name;
      }
  
      @Override
      public Hash.Algorithm algorithm() {
          switch (memoryPolicy) {
              case MemoryMappedBuffers:
                  return new AlgorithmWithMM();
              default:
                  return new Algorithm();
          }
      }
  
      @Override
      public Hash.Checksum checksum(int count) {
          return new Zah.Checksum(ByteBuffer.allocate(capacity(count)));
      }
  
      static int capacity(int count) {
          // Java 8: Long.BYTES
          return count * Long.SIZE / Byte.SIZE;
      }
  
      class Algorithm implements Hash.Algorithm {
  
          @Override
          public byte[] hash(byte[] array) {
              return HexUtils.toByteArray(hash.hashBytes(array));
          }
  
          @Override
          public byte[] hash(Path path) throws IOException {
              return hash(Files.readAllBytes(path));
          }
      }
  
      class AlgorithmWithMM implements Hash.Algorithm {
  
          @Override
          public byte[] hash(byte[] array) {
              return HexUtils.toByteArray(hash.hashBytes(array));
          }
  
          @Override
          public byte[] hash(Path path) throws IOException {
              try (FileChannel channel = FileChannel.open(path, READ);
                     CloseableBuffer buffer = CloseableBuffer.mappedBuffer(channel, READ_ONLY)) {
                 return HexUtils.toByteArray(hash.hashBytes(buffer.getBuffer()));
             }
         }
     }
 
     class Checksum implements Hash.Checksum {
 
         private final ByteBuffer buffer;
 
         Checksum(ByteBuffer buffer) {
             this.buffer = buffer;
         }
 
         @Override
         public void update(byte[] hash) {
             buffer.put(hash);
         }
 
         @Override
         public byte[] digest() {
             return HexUtils.toByteArray(hash.hashBytes(buffer, 0, buffer.position()));
         }
     }
 }