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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.parquet.column.values.delta;

import java.io.IOException;

import org.apache.parquet.bytes.ByteBufferAllocator;
import org.apache.parquet.bytes.BytesInput;
import org.apache.parquet.bytes.BytesUtils;
import org.apache.parquet.column.values.bitpacking.BytePackerForLong;
import org.apache.parquet.column.values.bitpacking.Packer;
import org.apache.parquet.io.ParquetEncodingException;

/**
 * Write longs (INT64) with delta encoding and binary packing.
 */
public class DeltaBinaryPackingValuesWriterForLong extends DeltaBinaryPackingValuesWriter {
  /**
   * max bitwidth for a mini block, it is used to allocate miniBlockByteBuffer which is
   * reused between flushes.
   */
  private static final int MAX_BITWIDTH = 64;

  /**
   * stores delta values starting from the 2nd value written(1st value is stored in header).
   * It's reused between flushes
   */
  private long[] deltaBlockBuffer;

  /**
   * firstValue is written to the header of the page
   */
  private long firstValue = 0;

  /**
   * cache previous written value for calculating delta
   */
  private long previousValue = 0;

  /**
   * min delta is written to the beginning of each block.
   * it's zig-zag encoded. The deltas stored in each block is actually the difference to min delta,
   * therefore are all positive
   * it will be reset after each flush
   */
  private long minDeltaInCurrentBlock = Long.MAX_VALUE;

  public DeltaBinaryPackingValuesWriterForLong(
      int slabSize, int pageSize, ByteBufferAllocator allocator) {
    this(DEFAULT_NUM_BLOCK_VALUES, DEFAULT_NUM_MINIBLOCKS, slabSize, pageSize, allocator);
  }

  public DeltaBinaryPackingValuesWriterForLong(int blockSizeInValues, int miniBlockNum, 
      int slabSize, int pageSize, ByteBufferAllocator allocator) {
    super(blockSizeInValues, miniBlockNum, slabSize, pageSize, allocator);
    deltaBlockBuffer = new long[config.blockSizeInValues];
    miniBlockByteBuffer = new byte[config.miniBlockSizeInValues * MAX_BITWIDTH];
  }

  @Override
  public void writeLong(long v) {
    totalValueCount++;

    if (totalValueCount == 1) {
      firstValue = v;
      previousValue = firstValue;
      return;
    }

    // Calculate delta. The possible overflow is accounted for. The algorithm is correct because
    // Java long is working as a modalar ring with base 2^64 and because of the plus and minus
    // properties of a ring. http://en.wikipedia.org/wiki/Modular_arithmetic#Integers_modulo_n
    long delta = v - previousValue;
    previousValue = v;

    deltaBlockBuffer[deltaValuesToFlush++] = delta;

    if (delta < minDeltaInCurrentBlock) {
      minDeltaInCurrentBlock = delta;
    }

    if (config.blockSizeInValues == deltaValuesToFlush) {
      flushBlockBuffer();
    }
  }

  private void flushBlockBuffer() {
    // since we store the min delta, the deltas will be converted to be the difference to min delta
    // and all positive
    for (int i = 0; i < deltaValuesToFlush; i++) {
      deltaBlockBuffer[i] = deltaBlockBuffer[i] - minDeltaInCurrentBlock;
    }

    writeMinDelta();
    int miniBlocksToFlush = getMiniBlockCountToFlush(deltaValuesToFlush);

    calculateBitWidthsForDeltaBlockBuffer(miniBlocksToFlush);
    for (int i = 0; i < config.miniBlockNumInABlock; i++) {
      writeBitWidthForMiniBlock(i);
    }

    for (int i = 0; i < miniBlocksToFlush; i++) {
      // writing i th miniblock
      int currentBitWidth = bitWidths[i];
      int blockOffset = 0;
      // TODO: should this cache the packer?
      BytePackerForLong packer = Packer.LITTLE_ENDIAN.newBytePackerForLong(currentBitWidth);
      int miniBlockStart = i * config.miniBlockSizeInValues;
      // pack values into the miniblock buffer, 8 at a time to get exactly currentBitWidth bytes
      for (int j = miniBlockStart; j < (i + 1) * config.miniBlockSizeInValues; j += 8) {
        // mini block is atomic in terms of flushing
        // This may write more values when reach to the end of data writing to last mini block,
        // since it may not be aligned to miniblock,
        // but doesn't matter. The reader uses total count to see if reached the end.
        packer.pack8Values(deltaBlockBuffer, j, miniBlockByteBuffer, blockOffset);
        blockOffset += currentBitWidth;
      }
      baos.write(miniBlockByteBuffer, 0, blockOffset);
    }

    minDeltaInCurrentBlock = Long.MAX_VALUE;
    deltaValuesToFlush = 0;
  }

  private void writeMinDelta() {
    try {
      BytesUtils.writeZigZagVarLong(minDeltaInCurrentBlock, baos);
    } catch (IOException e) {
      throw new ParquetEncodingException("can not write min delta for block", e);
    }
  }

  /**
   * iterate through values in each mini block and calculate the bitWidths of max values.
   *
   * @param miniBlocksToFlush number of miniblocks
   */
  private void calculateBitWidthsForDeltaBlockBuffer(int miniBlocksToFlush) {
    for (int miniBlockIndex = 0; miniBlockIndex < miniBlocksToFlush; miniBlockIndex++) {
      long mask = 0;
      int miniStart = miniBlockIndex * config.miniBlockSizeInValues;

      //The end of current mini block could be the end of current block(deltaValuesToFlush) buffer when data is not aligned to mini block
      int miniEnd = Math.min((miniBlockIndex + 1) * config.miniBlockSizeInValues, deltaValuesToFlush);

      for (int i = miniStart; i < miniEnd; i++) {
        mask |= deltaBlockBuffer[i];
      }
      bitWidths[miniBlockIndex] = 64 - Long.numberOfLeadingZeros(mask);
    }
  }

  /**
   * getBytes will trigger flushing block buffer, DO NOT write after getBytes() is called without calling reset()
   *
   * @return a BytesInput that contains the encoded page data
   */
  @Override
  public BytesInput getBytes() {
    // The Page Header should include: blockSizeInValues, numberOfMiniBlocks, totalValueCount
    if (deltaValuesToFlush != 0) {
      flushBlockBuffer();
    }
    return BytesInput.concat(
            config.toBytesInput(),
            BytesInput.fromUnsignedVarInt(totalValueCount),
            BytesInput.fromZigZagVarLong(firstValue),
            BytesInput.from(baos));
  }

  @Override
  public void reset() {
    super.reset();
    this.minDeltaInCurrentBlock = Long.MAX_VALUE;
  }

  @Override
  public void close() {
    super.close();
    this.minDeltaInCurrentBlock = Long.MAX_VALUE;
  }
}