/*
    * 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.eclipse.aether.connector.basic;
  
  import java.io.BufferedInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.nio.Buffer;
  import java.nio.ByteBuffer;
  import java.nio.file.Files;
  import java.nio.file.Path;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  
  import org.eclipse.aether.spi.connector.checksum.ChecksumAlgorithm;
  import org.eclipse.aether.spi.connector.checksum.ChecksumAlgorithmFactory;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * Calculates checksums for a downloaded file.
   */
  final class ChecksumCalculator {
  
      static class Checksum {
          final ChecksumAlgorithmFactory checksumAlgorithmFactory;
  
          ChecksumAlgorithm algorithm;
  
          Exception error;
  
          Checksum(ChecksumAlgorithmFactory checksumAlgorithmFactory) {
              this.checksumAlgorithmFactory = requireNonNull(checksumAlgorithmFactory);
              this.algorithm = checksumAlgorithmFactory.getAlgorithm();
          }
  
          public void reset() {
              this.algorithm = checksumAlgorithmFactory.getAlgorithm();
              this.error = null;
          }
  
          public void update(ByteBuffer buffer) {
              this.algorithm.update(buffer);
          }
  
          public void error(Exception error) {
              this.error = error;
          }
  
          public Object get() {
              if (error != null) {
                  return error;
              }
              return algorithm.checksum();
          }
      }
  
      private final List<Checksum> checksums;
  
      private final Path targetFile;
  
      public static ChecksumCalculator newInstance(
              Path targetFile, Collection<ChecksumAlgorithmFactory> checksumAlgorithmFactories) {
          if (checksumAlgorithmFactories == null || checksumAlgorithmFactories.isEmpty()) {
              return null;
          }
          return new ChecksumCalculator(targetFile, checksumAlgorithmFactories);
      }
  
      private ChecksumCalculator(Path targetFile, Collection<ChecksumAlgorithmFactory> checksumAlgorithmFactories) {
          this.checksums = new ArrayList<>();
          Set<String> algos = new HashSet<>();
          for (ChecksumAlgorithmFactory checksumAlgorithmFactory : checksumAlgorithmFactories) {
              if (algos.add(checksumAlgorithmFactory.getName())) {
                  this.checksums.add(new Checksum(checksumAlgorithmFactory));
              }
          }
          this.targetFile = targetFile;
     }
 
     public void init(long dataOffset) {
         for (Checksum checksum : checksums) {
             checksum.reset();
         }
         if (dataOffset <= 0L) {
             return;
         }
 
         try (InputStream in = new BufferedInputStream(Files.newInputStream(targetFile))) {
             long total = 0;
             final byte[] buffer = new byte[1024 * 32];
             while (total < dataOffset) {
                 int read = in.read(buffer);
                 if (read < 0) {
                     throw new IOException(targetFile + " contains only " + total
                             + " bytes, cannot resume download from offset " + dataOffset);
                 }
                 total += read;
                 if (total > dataOffset) {
                     read -= total - dataOffset;
                 }
                 update(ByteBuffer.wrap(buffer, 0, read));
             }
         } catch (IOException e) {
             for (Checksum checksum : checksums) {
                 checksum.error(e);
             }
         }
     }
 
     public void update(ByteBuffer data) {
         for (Checksum checksum : checksums) {
             ((Buffer) data).mark();
             checksum.update(data);
             ((Buffer) data).reset();
         }
     }
 
     public Map<String, Object> get() {
         Map<String, Object> results = new HashMap<>();
         for (Checksum checksum : checksums) {
             results.put(checksum.checksumAlgorithmFactory.getName(), checksum.get());
         }
         return results;
     }
 }