/**
 * Copyright 2014 National University of Ireland, Galway.
 *
 * This file is part of the SIREn project. Project and contact information:
 *
 *  https://github.com/rdelbru/SIREn
 *
 * 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 org.sindice.siren.analysis.filter;

import java.nio.ByteBuffer;
import java.nio.IntBuffer;

import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.IntsRef;
import org.sindice.siren.util.CodecUtils;

/**
 * An implementation of the {@link PayloadCodec} using Variable Int encoding.
 */
public class VIntPayloadCodec extends PayloadCodec {

  ByteBuffer bb = ByteBuffer.allocate(10);

  /**
   * Used in {@link #decode()} and {@link #encode()}
   */
  BytesRef bytes = new BytesRef();

  IntBuffer ib = IntBuffer.allocate(2);

  /**
   * Used in {@link #decode()} and {@link #encode()}
   */
  IntsRef ints = new IntsRef();

  int pos;

  @Override
  public IntsRef getNode() {
    return ints;
  }

  @Override
  public int getPosition() {
    return pos;
  }

  @Override
  public void decode(final BytesRef data) {
    // max case : 1 byte = 1 int
    this.ensureIntBufferSize(data.length);

    ib.clear();

    this.setData(data.bytes, data.offset, data.length);

    // decode position and node
    final int limit = bytes.length - bytes.offset;
    while (bytes.offset < limit) {
      ib.put(CodecUtils.byteArrayToVInt(bytes));
    }

    ib.flip();

    // set position
    pos = ib.get();

    // set node
    this.setNode(ib.array(), ib.position(), ib.limit() - ib.position());
  }

  @Override
  public BytesRef encode(final IntsRef node, final int pos) {
    // max case : 1 int = 5 bytes
    this.ensureByteBufferSize((node.length + 1) * 5);

    bb.clear();

    // encode position
    CodecUtils.vIntToByteArray(pos, bb);

    // encode node
    this.setNode(node.ints, node.offset, node.length);

    final int limit = ints.length - ints.offset;
    for (int i = ints.offset; i < limit; i++) {
      CodecUtils.vIntToByteArray(ints.ints[i], bb);
    }

    bb.flip();

    this.setData(bb.array(), bb.position(), bb.limit());

    return bytes;
  }

  private void setData(final byte[] data, final int offset, final int length) {
    bytes.bytes = data;
    bytes.length = length;
    bytes.offset = offset;
  }

  private void setNode(final int[] data, final int offset, final int length) {
    ints.ints = data;
    ints.length = length;
    ints.offset = offset;
  }

  private void ensureByteBufferSize(final int size) {
    if (bb.capacity() < size) {
      bb = ByteBuffer.allocate(size);
    }
  }

  private void ensureIntBufferSize(final int size) {
    if (ib.capacity() < size) {
      ib = IntBuffer.allocate(size);
    }
  }

}