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

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

/**
 * This class is a decoder for decoding the byte array that encoded by {@code RegularDataEncoder}.
 * RegularDataDecoder only supports integer and long values.

 * .
 *
 * @see RegularDataEncoder
 */
public abstract class RegularDataDecoder extends Decoder {

  /** the first value in one pack. */
  protected int readIntTotalCount = 0;

  protected int nextReadIndex = 0;
  /** data number in this pack. */
  protected int packNum;

  public RegularDataDecoder() {
    super(TSEncoding.REGULAR);
  }

  protected abstract void readHeader(ByteBuffer buffer) throws IOException;

  protected abstract void allocateDataArray();

  protected abstract void readValue(int i);

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

  public static class IntRegularDecoder extends RegularDataDecoder {

    private int[] data;
    private int firstValue;
    private int previous;
    private boolean isMissingPoint;
    private BitSet bitmap;
    private int bitmapIndex;
    /** minimum value for all difference. */
    private int minDeltaBase;

    public IntRegularDecoder() {
      super();
    }

    /**
     * if there's no decoded data left, decode next pack into {@code data}.
     *
     * @param buffer ByteBuffer
     * @return long value
     */
    protected int readT(ByteBuffer buffer) {
      if (nextReadIndex == readIntTotalCount) {
        isMissingPoint = ReadWriteIOUtils.readBool(buffer);
        if (isMissingPoint) {
          readBitmap(buffer);
        }
        return loadIntBatch(buffer); // load first value
      }
      if (isMissingPoint) {
        bitmapIndex++;
        return loadWithBitmap(buffer);
      }
      return data[nextReadIndex++];
    }

    private void readBitmap(ByteBuffer buffer) {
      int length = ReadWriteIOUtils.readInt(buffer);
      byte[] byteArr = new byte[length];
      buffer.get(byteArr);
      bitmap = BitSet.valueOf(byteArr);
      bitmapIndex = 0;
    }

    /**
     * load the data with bitmap (when bitmap denote the element with false, load next element)
     *
     * @param buffer
     * @return long value
     */
    protected int loadWithBitmap(ByteBuffer buffer) {
      while (!bitmap.get(bitmapIndex)) {
        bitmapIndex++;
      }
      nextReadIndex = bitmapIndex - 1;
      return data[nextReadIndex];
    }

    /**
     * if remaining data has been run out, load next pack from InputStream.
     *
     * @param buffer ByteBuffer
     * @return int value
     */
    protected int loadIntBatch(ByteBuffer buffer) {
      packNum = ReadWriteIOUtils.readInt(buffer);
      readHeader(buffer);

      allocateDataArray();

      readIntTotalCount = isMissingPoint ? (packNum - 2) : (packNum - 1);
      previous = firstValue;
      nextReadIndex = 0;
      readPack();
      return firstValue;
    }

    private void readPack() {
      for (int i = 0; i < data.length; i++) {
        readValue(i);
        previous = data[i];
      }
    }

    @Override
    public int readInt(ByteBuffer buffer) {
      return readT(buffer);
    }

    @Override
    protected void readHeader(ByteBuffer buffer) {
      minDeltaBase = ReadWriteIOUtils.readInt(buffer);
      firstValue = ReadWriteIOUtils.readInt(buffer);
    }

    @Override
    protected void allocateDataArray() {
      data = new int[packNum - 1];
    }

    @Override
    protected void readValue(int i) {
      data[i] = previous + minDeltaBase;
    }

    @Override
    public void reset() {
      // do nothing
    }
  }

  public static class LongRegularDecoder extends RegularDataDecoder {

    private long[] data;
    private long firstValue;
    private long previous;
    private boolean isMissingPoint;
    private BitSet bitmap;
    private int bitmapIndex;
    /** minimum value for all difference. */
    private long minDeltaBase;

    public LongRegularDecoder() {
      super();
    }

    /**
     * if there's no decoded data left, decode next pack into {@code data}.
     *
     * @param buffer ByteBuffer
     * @return long value
     */
    protected long readT(ByteBuffer buffer) {
      if (nextReadIndex == readIntTotalCount) {
        isMissingPoint = ReadWriteIOUtils.readBool(buffer);
        if (isMissingPoint) {
          readBitmap(buffer);
        }
        return loadIntBatch(buffer); // load first value
      }
      if (isMissingPoint) {
        bitmapIndex++;
        return loadWithBitmap(buffer);
      }
      return data[nextReadIndex++];
    }

    private void readBitmap(ByteBuffer buffer) {
      int length = ReadWriteIOUtils.readInt(buffer);
      byte[] byteArr = new byte[length];
      buffer.get(byteArr);
      bitmap = BitSet.valueOf(byteArr);
      bitmapIndex = 0;
    }

    /**
     * load the data with bitmap (when bitmap denote the element with false, load next element)
     *
     * @param buffer
     * @return long value
     */
    protected long loadWithBitmap(ByteBuffer buffer) {
      while (!bitmap.get(bitmapIndex)) {
        bitmapIndex++;
      }
      nextReadIndex = bitmapIndex - 1;
      return data[nextReadIndex];
    }

    /**
     * if remaining data has been run out, load next pack from InputStream.
     *
     * @param buffer ByteBuffer
     * @return long value
     */
    protected long loadIntBatch(ByteBuffer buffer) {
      packNum = ReadWriteIOUtils.readInt(buffer);
      readHeader(buffer);

      allocateDataArray();

      readIntTotalCount = isMissingPoint ? (packNum - 2) : (packNum - 1);
      previous = firstValue;
      nextReadIndex = 0;
      readPack();
      return firstValue;
    }

    private void readPack() {
      for (int i = 0; i < data.length; i++) {
        readValue(i);
        previous = data[i];
      }
    }

    @Override
    public long readLong(ByteBuffer buffer) {
      return readT(buffer);
    }

    @Override
    protected void readHeader(ByteBuffer buffer) {
      minDeltaBase = ReadWriteIOUtils.readLong(buffer);
      firstValue = ReadWriteIOUtils.readLong(buffer);
    }

    @Override
    protected void allocateDataArray() {
      data = new long[packNum - 1];
    }

    @Override
    protected void readValue(int i) {
      data[i] = previous + minDeltaBase;
    }

    @Override
    public void reset() {
      // do nothing
    }
  }
}