/*
 * Copyright 2014 The gRPC Authors
 *
 * Licensed 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 io.grpc.internal;

import java.io.Closeable;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import javax.annotation.Nullable;

/**
 * Interface for an abstract byte buffer. Buffers are intended to be a read-only, except for the
 * read position which is incremented after each read call.
 *
 * <p>Buffers may optionally expose a backing array for optimization purposes, similar to what is
 * done in {@link ByteBuffer}. It is not expected that callers will attempt to modify the backing
 * array.
 */
public interface ReadableBuffer extends Closeable {

  /**
   * Gets the current number of readable bytes remaining in this buffer.
   */
  int readableBytes();

  /**
   * Reads the next unsigned byte from this buffer and increments the read position by 1.
   *
   * @throws IndexOutOfBoundsException if required bytes are not readable
   */
  int readUnsignedByte();

  /**
   * Reads a 4-byte signed integer from this buffer using big-endian byte ordering. Increments the
   * read position by 4.
   *
   * @throws IndexOutOfBoundsException if required bytes are not readable
   */
  int readInt();

  /**
   * Increments the read position by the given length.
   *
   * @throws IndexOutOfBoundsException if required bytes are not readable
   */
  void skipBytes(int length);

  /**
   * Reads {@code length} bytes from this buffer and writes them to the destination array.
   * Increments the read position by {@code length}.
   *
   * @param dest the destination array to receive the bytes.
   * @param destOffset the starting offset in the destination array.
   * @param length the number of bytes to be copied.
   * @throws IndexOutOfBoundsException if required bytes are not readable or {@code dest} is too
   *     small.
   */
  void readBytes(byte[] dest, int destOffset, int length);

  /**
   * Reads from this buffer until the destination's position reaches its limit, and increases the
   * read position by the number of the transferred bytes.
   *
   * @param dest the destination buffer to receive the bytes.
   * @throws IndexOutOfBoundsException if required bytes are not readable
   */
  void readBytes(ByteBuffer dest);

  /**
   * Reads {@code length} bytes from this buffer and writes them to the destination stream.
   * Increments the read position by {@code length}. If the required bytes are not readable, throws
   * {@link IndexOutOfBoundsException}.
   *
   * @param dest the destination stream to receive the bytes.
   * @param length the number of bytes to be copied.
   * @throws IOException thrown if any error was encountered while writing to the stream.
   * @throws IndexOutOfBoundsException if required bytes are not readable
   */
  void readBytes(OutputStream dest, int length) throws IOException;

  /**
   * Reads {@code length} bytes from this buffer and returns a new Buffer containing them. Some
   * implementations may return a Buffer sharing the backing memory with this buffer to prevent
   * copying. However, that means that the returned buffer may keep the (possibly much larger)
   * backing memory in use even after this buffer is closed.
   *
   * @param length the number of bytes to contain in returned Buffer.
   * @throws IndexOutOfBoundsException if required bytes are not readable
   */
  ReadableBuffer readBytes(int length);

  /**
   * Indicates whether or not this buffer exposes a backing array.
   */
  boolean hasArray();

  /**
   * Gets the backing array for this buffer. This is an optional method, so callers should first
   * check {@link #hasArray}.
   *
   * @throws UnsupportedOperationException the buffer does not support this method
   */
  byte[] array();

  /**
   * Gets the offset in the backing array of the current read position. This is an optional method,
   * so callers should first check {@link #hasArray}
   *
   * @throws UnsupportedOperationException the buffer does not support this method
   */
  int arrayOffset();

  /**
   * Note that the current callsite has access to this buffer, or do nothing. This is only useful
   * when the buffer has leak detection and intrumentation to record usages before the buffer was
   * leaked. That can make it much easier to track down where the buffer was leaked. If this isn't
   * such a buffer, the method does nothing.
   */
  default void touch() {}

  /**
   * Indicates whether or not {@link #mark} operation is supported for this buffer.
   */
  boolean markSupported();

  /**
   * Marks the current position in this buffer. A subsequent call to the {@link #reset} method
   * repositions this stream at the last marked position so that subsequent reads re-read the same
   * bytes.
   */
  void mark();

  /**
   * Repositions this buffer to the position at the time {@link #mark} was last called on this
   * buffer.
   */
  void reset();

  /**
   * Indicates whether or not {@link #getByteBuffer} operation is supported for this buffer.
   */
  boolean byteBufferSupported();

  /**
   * Gets a {@link ByteBuffer} that contains some bytes of the content next to be read, or {@code
   * null} if this buffer has been exhausted. The number of bytes contained in the returned buffer
   * is implementation specific. The position of this buffer is unchanged after calling this
   * method. The returned buffer's content should not be modified, but the position, limit, and
   * mark may be changed. Operations for changing the position, limit, and mark of the returned
   * buffer does not affect the position, limit, and mark of this buffer. Buffers returned by this
   * method have independent position, limit and mark. This is an optional method, so callers
   * should first check {@link #byteBufferSupported}.
   *
   * @throws UnsupportedOperationException the buffer does not support this method.
   */
  @Nullable
  ByteBuffer getByteBuffer();

  /**
   * Closes this buffer and releases any resources.
   */
  @Override
  void close();
}
