/* 
 * 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.boundedint;

import static org.apache.parquet.Log.DEBUG;

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

import org.apache.parquet.Log;
import org.apache.parquet.bytes.BytesUtils;
import org.apache.parquet.column.values.ValuesReader;
import org.apache.parquet.io.ParquetDecodingException;

/**
 * @see BoundedIntValuesWriter
 */
class BoundedIntValuesReader extends ValuesReader {
  private static final Log LOG = Log.getLog(BoundedIntValuesReader.class);

  private int currentValueCt = 0;
  private int currentValue = 0;
  private final int bitsPerValue;
  private BitReader bitReader = new BitReader();
  private int nextOffset;

  public BoundedIntValuesReader(int bound) {
    if (bound == 0) {
      throw new ParquetDecodingException("Value bound cannot be 0. Use DevNullColumnReader instead.");
    }
    bitsPerValue = BytesUtils.getWidthFromMaxInt(bound);
  }

  @Override
  public int readInteger() {
    try {
      if (currentValueCt > 0) {
        currentValueCt--;
        return currentValue;
      }
      if (bitReader.readBit()) {
        currentValue = bitReader.readNBitInteger(bitsPerValue);
        currentValueCt = bitReader.readUnsignedVarint() - 1;
      } else {
        currentValue = bitReader.readNBitInteger(bitsPerValue);
      }
      return currentValue;
    } catch (IOException e) {
      throw new ParquetDecodingException("could not read int", e);
    }
  }

  // This forces it to deserialize into memory. If it wanted
  // to, it could just read the bytes (though that number of
  // bytes would have to be serialized). This is the flip-side
  // to BoundedIntColumnWriter.writeData(BytesOutput)
  @Override
  public void initFromPage(int valueCount, ByteBuffer in, int offset) throws IOException {
    if (DEBUG) LOG.debug("reading size at "+ offset + ": " + in.get(offset) + " " + in.get(offset + 1) + " " + in.get(offset + 2) + " " + in.get(offset + 3) + " ");
    int totalBytes = BytesUtils.readIntLittleEndian(in, offset);
    if (DEBUG) LOG.debug("will read "+ totalBytes + " bytes");
    currentValueCt = 0;
    currentValue = 0;
    bitReader.prepare(in, offset + 4, totalBytes);
    if (DEBUG) LOG.debug("will read next from " + (offset + totalBytes + 4));
    this.nextOffset = offset + totalBytes + 4;
  }
  
  @Override
  public int getNextOffset() {
    return this.nextOffset;
  }

  @Override
  public void skip() {
    readInteger();
  }
}