/*
    * Copyright 2016 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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 io.netty5.handler.codec.compression;
  
  import io.netty5.buffer.api.Buffer;
  
  import java.nio.ByteBuffer;
  import java.util.zip.Checksum;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * {@link Checksum} implementation which can directly act on a {@link Buffer}.
   */
  class BufferChecksum implements Checksum {
  
      private final Checksum checksum;
  
      BufferChecksum(Checksum checksum) {
          this.checksum = requireNonNull(checksum);
      }
  
      @Override
      public void update(int b) {
          checksum.update(b);
      }
  
      @Override
      public void update(byte[] b, int off, int len) {
          checksum.update(b, off, len);
      }
  
      @Override
      public long getValue() {
          return checksum.getValue();
      }
  
      @Override
      public void reset() {
          checksum.reset();
      }
  
      /**
       * @see #update(byte[], int, int)
       */
      public void update(Buffer b, int off, int len) {
          int readerOffset = b.readerOffset();
          b.readerOffset(off);
          try {
              try (var iteration = b.forEachReadable()) {
                  for (var c = iteration.first(); c != null; c = c.next()) {
                      ByteBuffer componentBuffer = c.readableBuffer();
                      if (componentBuffer.remaining() > len) {
                          componentBuffer.limit(componentBuffer.position() + len);
                          update(componentBuffer);
                          break;
                      } else {
                          len -= componentBuffer.remaining();
                          update(componentBuffer);
                      }
                  }
              }
          } finally {
              b.readerOffset(readerOffset);
          }
      }
  }