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// Copyright 2015-2024 Nstream, inc.
//
// 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 nstream.persist.api.kv;

import java.nio.ByteBuffer;

/**
 * Wrapper around a pair of buffers to read the current key-value pair from a {@link MapIterator}.
 */
public class KeyValueBuffers {

  private ByteBuffer keyBuffer;
  private ByteBuffer valueBuffer;

  /**
   * @param keyBuffer Initial key buffer.
   * @param valueBuffer Initial value buffer.
   */
  public KeyValueBuffers(ByteBuffer keyBuffer, ByteBuffer valueBuffer) {
    if (keyBuffer == null || valueBuffer == null) {
      throw new NullPointerException("Buffers must be non-null.");
    }
    this.keyBuffer = keyBuffer;
    this.valueBuffer = valueBuffer;
  }

  public ByteBuffer getKeyBuffer() {
    return this.keyBuffer;
  }

  public ByteBuffer getValueBuffer() {
    return this.valueBuffer;
  }

  public void setKeyBuffer(ByteBuffer buffer) {
    if (buffer == null) {
      throw new NullPointerException("Buffers must no non-null.");
    }
    this.keyBuffer = buffer;
  }

  public void setValueBuffer(ByteBuffer buffer) {
    if (buffer == null) {
      throw new NullPointerException("Buffers must no non-null.");
    }
    this.valueBuffer = buffer;
  }

  private static final int MIN_BUFFER = 8;
  private static final int MULTIPLE = 2;

  private static ByteBuffer grow(ByteBuffer buf, int required) {
    final var newSize = Integer.max(Integer.max(MIN_BUFFER, required), buf.capacity() * MULTIPLE);
    if (buf.isDirect()) {
      return ByteBuffer.allocateDirect(newSize);
    } else {
      return ByteBuffer.allocate(newSize);
    }
  }

  /**
   * Grow the key buffer to be able to accept the specified number of bytes.
   * @param n The number of bytes.
   */
  public void growKey(int n) {
    this.keyBuffer = grow(this.keyBuffer, n);
  }

  /**
   * Grow the key buffer by a default multiplier (when the number of bytes required is unknown).
   */
  public void growKey() {
    this.growKey(-1);
  }

  /**
   * Grow the value buffer to be able to accept the specified number of bytes.
   * @param n The number of bytes.
   */
  public void growValue(int n) {
    this.valueBuffer = grow(this.valueBuffer, n);
  }

  /**
   * Grow the value buffer by a default multiplier (when the number of bytes required is unknown).
   */
  public void growValue() {
    this.growValue(-1);
  }

}