/**
 * 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.orc.impl;

import java.io.EOFException;
import java.io.IOException;
import java.util.Arrays;

import org.apache.hadoop.hive.ql.exec.vector.ColumnVector;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * A reader that reads a sequence of light weight compressed integers. Refer
 * {@link RunLengthIntegerWriterV2} for description of various lightweight
 * compression techniques.
 */
public class RunLengthIntegerReaderV2 implements IntegerReader {
  public static final Logger LOG = LoggerFactory.getLogger(RunLengthIntegerReaderV2.class);

  private InStream input;
  private final boolean signed;
  private final long[] literals = new long[RunLengthIntegerWriterV2.MAX_SCOPE];
  private boolean isRepeating = false;
  private int numLiterals = 0;
  private int used = 0;
  private final boolean skipCorrupt;
  private final SerializationUtils utils;
  private RunLengthIntegerWriterV2.EncodingType currentEncoding;

  public RunLengthIntegerReaderV2(InStream input, boolean signed,
      boolean skipCorrupt) throws IOException {
    this.input = input;
    this.signed = signed;
    this.skipCorrupt = skipCorrupt;
    this.utils = new SerializationUtils();
  }

  private final static RunLengthIntegerWriterV2.EncodingType[] encodings = RunLengthIntegerWriterV2.EncodingType.values();
  private void readValues(boolean ignoreEof) throws IOException {
    // read the first 2 bits and determine the encoding type
    isRepeating = false;
    int firstByte = input.read();
    if (firstByte < 0) {
      if (!ignoreEof) {
        throw new EOFException("Read past end of RLE integer from " + input);
      }
      used = numLiterals = 0;
      return;
    }
    currentEncoding = encodings[(firstByte >>> 6) & 0x03];
    switch (currentEncoding) {
    case SHORT_REPEAT: readShortRepeatValues(firstByte); break;
    case DIRECT: readDirectValues(firstByte); break;
    case PATCHED_BASE: readPatchedBaseValues(firstByte); break;
    case DELTA: readDeltaValues(firstByte); break;
    default: throw new IOException("Unknown encoding " + currentEncoding);
    }
  }

  private void readDeltaValues(int firstByte) throws IOException {

    // extract the number of fixed bits
    int fb = (firstByte >>> 1) & 0x1f;
    if (fb != 0) {
      fb = utils.decodeBitWidth(fb);
    }

    // extract the blob run length
    int len = (firstByte & 0x01) << 8;
    len |= input.read();

    // read the first value stored as vint
    long firstVal = 0;
    if (signed) {
      firstVal = utils.readVslong(input);
    } else {
      firstVal = utils.readVulong(input);
    }

    // store first value to result buffer
    long prevVal = firstVal;
    literals[numLiterals++] = firstVal;

    // if fixed bits is 0 then all values have fixed delta
    if (fb == 0) {
      // read the fixed delta value stored as vint (deltas can be negative even
      // if all number are positive)
      long fd = utils.readVslong(input);
      if (fd == 0) {
        isRepeating = true;
        assert numLiterals == 1;
        Arrays.fill(literals, numLiterals, numLiterals + len, literals[0]);
        numLiterals += len;
      } else {
        // add fixed deltas to adjacent values
        for(int i = 0; i < len; i++) {
          literals[numLiterals++] = literals[numLiterals - 2] + fd;
        }
      }
    } else {
      long deltaBase = utils.readVslong(input);
      // add delta base and first value
      literals[numLiterals++] = firstVal + deltaBase;
      prevVal = literals[numLiterals - 1];
      len -= 1;

      // write the unpacked values, add it to previous value and store final
      // value to result buffer. if the delta base value is negative then it
      // is a decreasing sequence else an increasing sequence
      utils.readInts(literals, numLiterals, len, fb, input);
      while (len > 0) {
        if (deltaBase < 0) {
          literals[numLiterals] = prevVal - literals[numLiterals];
        } else {
          literals[numLiterals] = prevVal + literals[numLiterals];
        }
        prevVal = literals[numLiterals];
        len--;
        numLiterals++;
      }
    }
  }

  private void readPatchedBaseValues(int firstByte) throws IOException {

    // extract the number of fixed bits
    int fbo = (firstByte >>> 1) & 0x1f;
    int fb = utils.decodeBitWidth(fbo);

    // extract the run length of data blob
    int len = (firstByte & 0x01) << 8;
    len |= input.read();
    // runs are always one off
    len += 1;

    // extract the number of bytes occupied by base
    int thirdByte = input.read();
    int bw = (thirdByte >>> 5) & 0x07;
    // base width is one off
    bw += 1;

    // extract patch width
    int pwo = thirdByte & 0x1f;
    int pw = utils.decodeBitWidth(pwo);

    // read fourth byte and extract patch gap width
    int fourthByte = input.read();
    int pgw = (fourthByte >>> 5) & 0x07;
    // patch gap width is one off
    pgw += 1;

    // extract the length of the patch list
    int pl = fourthByte & 0x1f;

    // read the next base width number of bytes to extract base value
    long base = utils.bytesToLongBE(input, bw);
    long mask = (1L << ((bw * 8) - 1));
    // if MSB of base value is 1 then base is negative value else positive
    if ((base & mask) != 0) {
      base = base & ~mask;
      base = -base;
    }

    // unpack the data blob
    long[] unpacked = new long[len];
    utils.readInts(unpacked, 0, len, fb, input);

    // unpack the patch blob
    long[] unpackedPatch = new long[pl];

    if ((pw + pgw) > 64 && !skipCorrupt) {
      throw new IOException("Corruption in ORC data encountered. To skip" +
          " reading corrupted data, set hive.exec.orc.skip.corrupt.data to" +
          " true");
    }
    int bitSize = utils.getClosestFixedBits(pw + pgw);
    utils.readInts(unpackedPatch, 0, pl, bitSize, input);

    // apply the patch directly when decoding the packed data
    int patchIdx = 0;
    long currGap = 0;
    long currPatch = 0;
    long patchMask = ((1L << pw) - 1);
    currGap = unpackedPatch[patchIdx] >>> pw;
    currPatch = unpackedPatch[patchIdx] & patchMask;
    long actualGap = 0;

    // special case: gap is >255 then patch value will be 0.
    // if gap is <=255 then patch value cannot be 0
    while (currGap == 255 && currPatch == 0) {
      actualGap += 255;
      patchIdx++;
      currGap = unpackedPatch[patchIdx] >>> pw;
      currPatch = unpackedPatch[patchIdx] & patchMask;
    }
    // add the left over gap
    actualGap += currGap;

    // unpack data blob, patch it (if required), add base to get final result
    for(int i = 0; i < unpacked.length; i++) {
      if (i == actualGap) {
        // extract the patch value
        long patchedVal = unpacked[i] | (currPatch << fb);

        // add base to patched value
        literals[numLiterals++] = base + patchedVal;

        // increment the patch to point to next entry in patch list
        patchIdx++;

        if (patchIdx < pl) {
          // read the next gap and patch
          currGap = unpackedPatch[patchIdx] >>> pw;
          currPatch = unpackedPatch[patchIdx] & patchMask;
          actualGap = 0;

          // special case: gap is >255 then patch will be 0. if gap is
          // <=255 then patch cannot be 0
          while (currGap == 255 && currPatch == 0) {
            actualGap += 255;
            patchIdx++;
            currGap = unpackedPatch[patchIdx] >>> pw;
            currPatch = unpackedPatch[patchIdx] & patchMask;
          }
          // add the left over gap
          actualGap += currGap;

          // next gap is relative to the current gap
          actualGap += i;
        }
      } else {
        // no patching required. add base to unpacked value to get final value
        literals[numLiterals++] = base + unpacked[i];
      }
    }

  }

  private void readDirectValues(int firstByte) throws IOException {

    // extract the number of fixed bits
    int fbo = (firstByte >>> 1) & 0x1f;
    int fb = utils.decodeBitWidth(fbo);

    // extract the run length
    int len = (firstByte & 0x01) << 8;
    len |= input.read();
    // runs are one off
    len += 1;

    // write the unpacked values and zigzag decode to result buffer
    utils.readInts(literals, numLiterals, len, fb, input);
    if (signed) {
      for(int i = 0; i < len; i++) {
        literals[numLiterals] = utils.zigzagDecode(literals[numLiterals]);
        numLiterals++;
      }
    } else {
      numLiterals += len;
    }
  }

  private void readShortRepeatValues(int firstByte) throws IOException {

    // read the number of bytes occupied by the value
    int size = (firstByte >>> 3) & 0x07;
    // #bytes are one off
    size += 1;

    // read the run length
    int len = firstByte & 0x07;
    // run lengths values are stored only after MIN_REPEAT value is met
    len += RunLengthIntegerWriterV2.MIN_REPEAT;

    // read the repeated value which is store using fixed bytes
    long val = utils.bytesToLongBE(input, size);

    if (signed) {
      val = utils.zigzagDecode(val);
    }

    if (numLiterals != 0) {
      // Currently this always holds, which makes peekNextAvailLength simpler.
      // If this changes, peekNextAvailLength should be adjusted accordingly.
      throw new AssertionError("readValues called with existing values present");
    }
    // repeat the value for length times
    isRepeating = true;
    // TODO: this is not so useful and V1 reader doesn't do that. Fix? Same if delta == 0
    for(int i = 0; i < len; i++) {
      literals[i] = val;
    }
    numLiterals = len;
  }

  @Override
  public boolean hasNext() throws IOException {
    return used != numLiterals || input.available() > 0;
  }

  @Override
  public long next() throws IOException {
    long result;
    if (used == numLiterals) {
      numLiterals = 0;
      used = 0;
      readValues(false);
    }
    result = literals[used++];
    return result;
  }

  @Override
  public void seek(PositionProvider index) throws IOException {
    input.seek(index);
    int consumed = (int) index.getNext();
    if (consumed != 0) {
      // a loop is required for cases where we break the run into two
      // parts
      while (consumed > 0) {
        numLiterals = 0;
        readValues(false);
        used = consumed;
        consumed -= numLiterals;
      }
    } else {
      used = 0;
      numLiterals = 0;
    }
  }

  @Override
  public void skip(long numValues) throws IOException {
    while (numValues > 0) {
      if (used == numLiterals) {
        numLiterals = 0;
        used = 0;
        readValues(false);
      }
      long consume = Math.min(numValues, numLiterals - used);
      used += consume;
      numValues -= consume;
    }
  }

  @Override
  public void nextVector(ColumnVector previous,
                         long[] data,
                         int previousLen) throws IOException {
    // if all nulls, just return
    if (previous.isRepeating && !previous.noNulls && previous.isNull[0]) {
      return;
    }
    previous.isRepeating = true;
    for (int i = 0; i < previousLen; i++) {
      if (previous.noNulls || !previous.isNull[i]) {
        data[i] = next();
      } else {
        // The default value of null for int type in vectorized
        // processing is 1, so set that if the value is null
        data[i] = 1;
      }

      // The default value for nulls in Vectorization for int types is 1
      // and given that non null value can also be 1, we need to check for isNull also
      // when determining the isRepeating flag.
      if (previous.isRepeating
          && i > 0
          && (data[0] != data[i] ||
          previous.isNull[0] != previous.isNull[i])) {
        previous.isRepeating = false;
      }
    }
  }

  @Override
  public void nextVector(ColumnVector vector,
                         int[] data,
                         int size) throws IOException {
    if (vector.noNulls) {
      for(int r=0; r < data.length && r < size; ++r) {
        data[r] = (int) next();
      }
    } else if (!(vector.isRepeating && vector.isNull[0])) {
      for(int r=0; r < data.length && r < size; ++r) {
        if (!vector.isNull[r]) {
          data[r] = (int) next();
        } else {
          data[r] = 1;
        }
      }
    }
  }
}
