/*
    * 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
    *
    *      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 org.apache.commons.io.channels;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.nio.channels.FileChannel;
  
  /**
   * Always reads the same amount of bytes on each call (or less).
   */
  class FixedReadSizeFileChannelProxy extends FileChannelProxy {
  
      final int readSize;
  
      FixedReadSizeFileChannelProxy(final FileChannel fileChannel, final int readSize) {
          super(fileChannel);
          if (readSize < 1) {
              throw new IllegalArgumentException("readSize: " + readSize);
          }
          this.readSize = readSize;
      }
  
      @Override
      public int read(final ByteBuffer dst) throws IOException {
          final int saveLimit = dst.limit();
          dst.limit(Math.min(dst.position() + readSize, dst.capacity()));
          if (!dst.hasRemaining()) {
              throw new IllegalStateException("Programming error.");
          }
          final int numRead = super.read(dst);
          if (numRead > readSize) {
              throw new IllegalStateException(String.format("numRead %,d > readSize %,d", numRead, readSize));
          }
          dst.limit(saveLimit);
          return numRead;
      }
  
      @Override
      public int read(final ByteBuffer dst, final long position) throws IOException {
          final int saveLimit = dst.limit();
          dst.limit(Math.min(dst.position() + readSize, dst.capacity()));
          if (!dst.hasRemaining()) {
              throw new IllegalStateException("Programming error.");
          }
          final int numRead = super.read(dst, position);
          if (numRead > readSize) {
              throw new IllegalStateException(String.format("numRead %,d > readSize %,d", numRead, readSize));
          }
          dst.limit(saveLimit);
          return numRead;
      }
  
      @Override
      public long read(final ByteBuffer[] dsts, final int offset, final int length) throws IOException {
          throw new UnsupportedOperationException();
      }
  }