/*
    * 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.commons.io.input.buffer;
  
  import static org.apache.commons.io.IOUtils.EOF;
  
  import java.io.BufferedInputStream;
  import java.io.FilterInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.util.Objects;
  
  import org.apache.commons.io.IOUtils;
  
  /**
   * Implements a buffered input stream, which is internally based on a {@link CircularByteBuffer}. Unlike the
   * {@link BufferedInputStream}, this one doesn't need to reallocate byte arrays internally.
   *
   * @since 2.7
   */
  public class CircularBufferInputStream extends FilterInputStream {
  
      /** Internal buffer. */
      protected final CircularByteBuffer buffer;
  
      /** Internal buffer size. */
      protected final int bufferSize;
  
      /** Whether we've seen the input stream EOF. */
      private boolean eof;
  
      /**
       * Constructs a new instance, which filters the given input stream, and uses a reasonable default buffer size
       * ({@link IOUtils#DEFAULT_BUFFER_SIZE}).
       *
       * @param inputStream The input stream, which is being buffered.
       */
      public CircularBufferInputStream(final InputStream inputStream) {
          this(inputStream, IOUtils.DEFAULT_BUFFER_SIZE);
      }
  
      /**
       * Constructs a new instance, which filters the given input stream, and uses the given buffer size.
       *
       * @param inputStream The input stream, which is being buffered.
       * @param bufferSize The size of the {@link CircularByteBuffer}, which is used internally.
       */
      @SuppressWarnings("resource") // Caller closes InputStream
      public CircularBufferInputStream(final InputStream inputStream, final int bufferSize) {
          super(Objects.requireNonNull(inputStream, "inputStream"));
          if (bufferSize <= 0) {
              throw new IllegalArgumentException("Illegal bufferSize: " + bufferSize);
          }
          this.buffer = new CircularByteBuffer(bufferSize);
          this.bufferSize = bufferSize;
          this.eof = false;
      }
  
      @Override
      public void close() throws IOException {
          super.close();
          eof = true;
          buffer.clear();
      }
  
      /**
       * Fills the buffer with the contents of the input stream.
       *
       * @throws IOException in case of an error while reading from the input stream.
       */
      protected void fillBuffer() throws IOException {
          if (eof) {
              return;
          }
          int space = buffer.getSpace();
          final byte[] buf = IOUtils.byteArray(space);
          while (space > 0) {
              final int res = in.read(buf, 0, space);
              if (res == EOF) {
                  eof = true;
                  return;
              }
              if (res > 0) {
                  buffer.add(buf, 0, res);
                  space -= res;
             }
         }
     }
 
     /**
      * Fills the buffer from the input stream until the given number of bytes have been added to the buffer.
      *
      * @param count number of byte to fill into the buffer
      * @return true if the buffer has bytes
      * @throws IOException in case of an error while reading from the input stream.
      */
     protected boolean haveBytes(final int count) throws IOException {
         if (buffer.getCurrentNumberOfBytes() < count) {
             fillBuffer();
         }
         return buffer.hasBytes();
     }
 
     @Override
     public int read() throws IOException {
         if (!haveBytes(1)) {
             return EOF;
         }
         return buffer.read() & 0xFF; // return unsigned byte
     }
 
     @Override
     public int read(final byte[] targetBuffer, final int offset, final int length) throws IOException {
         Objects.requireNonNull(targetBuffer, "targetBuffer");
         if (offset < 0) {
             throw new IllegalArgumentException("Offset must not be negative");
         }
         if (length < 0) {
             throw new IllegalArgumentException("Length must not be negative");
         }
         if (!haveBytes(length)) {
             return EOF;
         }
         final int result = Math.min(length, buffer.getCurrentNumberOfBytes());
         for (int i = 0; i < result; i++) {
             targetBuffer[offset + i] = buffer.read();
         }
         return result;
     }
 }