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A columnar file format designed for time-series data
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/*
 * 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.tsfile.encoding.decoder;

import org.apache.tsfile.file.metadata.enums.TSEncoding;
import org.apache.tsfile.utils.ReadWriteIOUtils;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.nio.ByteBuffer;

public abstract class GorillaDecoderV1 extends Decoder {

  protected static final int EOF = -1;
  private static final Logger logger = LoggerFactory.getLogger(GorillaDecoderV1.class);
  // flag to indicate whether the first value is read from stream
  protected boolean flag;
  protected int leadingZeroNum;
  protected int tailingZeroNum;
  protected boolean isEnd;
  // 8-bit buffer of bits to write out
  protected int buffer;
  // number of bits remaining in buffer
  protected int numberLeftInBuffer;

  protected boolean nextFlag1;
  protected boolean nextFlag2;

  protected GorillaDecoderV1() {
    super(TSEncoding.GORILLA_V1);
    reset();
  }

  @Override
  public void reset() {
    this.flag = false;
    this.isEnd = false;
    this.numberLeftInBuffer = 0;
  }

  @Override
  public boolean hasNext(ByteBuffer buffer) throws IOException {
    return buffer.remaining() > 0 || !isEnd;
  }

  protected boolean isEmpty() {
    return buffer == EOF;
  }

  protected boolean readBit(ByteBuffer buffer) throws IOException {
    if (numberLeftInBuffer == 0 && !isEnd) {
      fillBuffer(buffer);
    }
    if (isEmpty()) {
      throw new IOException("Reading from empty buffer");
    }
    numberLeftInBuffer--;
    return ((this.buffer >> numberLeftInBuffer) & 1) == 1;
  }

  /**
   * read one byte and save it in the buffer.
   *
   * @param buffer ByteBuffer to read
   */
  protected void fillBuffer(ByteBuffer buffer) {
    if (buffer.remaining() >= 1) {
      this.buffer = ReadWriteIOUtils.read(buffer);
      numberLeftInBuffer = 8;
    } else {
      logger.error("Failed to fill a new buffer, because there is no byte to read");
      this.buffer = EOF;
      numberLeftInBuffer = -1;
    }
  }

  /**
   * read some bits and convert them to an int value.
   *
   * @param buffer stream to read
   * @param len number of bit to read
   * @return converted int value
   * @throws IOException cannot read from stream
   */
  protected int readIntFromStream(ByteBuffer buffer, int len) throws IOException {
    int num = 0;
    for (int i = 0; i < len; i++) {
      int bit = readBit(buffer) ? 1 : 0;
      num |= bit << (len - 1 - i);
    }
    return num;
  }

  /**
   * read some bits and convert them to a long value.
   *
   * @param buffer stream to read
   * @param len number of bit to read
   * @return converted long value
   * @throws IOException cannot read from stream
   */
  protected long readLongFromStream(ByteBuffer buffer, int len) throws IOException {
    long num = 0;
    for (int i = 0; i < len; i++) {
      long bit = readBit(buffer) ? 1 : 0;
      num |= bit << (len - 1 - i);
    }
    return num;
  }
}