lang/java/trevni/core/src/main/java/org/apache/trevni/ColumnDescriptor.java

/**
 * 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.trevni;

import java.io.IOException;

import java.util.Arrays;

class ColumnDescriptor<T extends Comparable> {
  final Input file;
  final ColumnMetaData metaData;

  long start;
  long dataStart;

  BlockDescriptor[] blocks;

  long[] blockStarts;                             // for random access
  long[] firstRows;                               // for binary searches
  T[] firstValues;                                // for binary searches

  public ColumnDescriptor(Input file, ColumnMetaData metaData) {
    this.file = file;
    this.metaData = metaData;
  }

  public int findBlock(long row) {
    int block = Arrays.binarySearch(firstRows, row);
    if (block < 0)
      block = -block - 2;
    return block;
  }

  public int findBlock(T value) {
    int block = Arrays.binarySearch(firstValues, value);
    if (block < 0)
      block = -block - 2;
    return block;
  }

  public int blockCount() { return blocks.length; }

  public long lastRow(int block) {
    if (blocks.length == 0 || block < 0) return 0;
    return firstRows[block] + blocks[block].rowCount;
  }

  public void ensureBlocksRead() throws IOException {
    if (blocks != null) return;

    // read block descriptors
    InputBuffer in = new InputBuffer(file, start);
    int blockCount = in.readFixed32();
    BlockDescriptor[] blocks = new BlockDescriptor[blockCount];
    if (metaData.hasIndexValues())
      firstValues = (T[])new Comparable[blockCount];

    for (int i = 0; i < blockCount; i++) {
      blocks[i] = BlockDescriptor.read(in);
      if (metaData.hasIndexValues())
        firstValues[i] = in.<T>readValue(metaData.getType());
    }
    dataStart = in.tell();

    // compute blockStarts and firstRows
    Checksum checksum = Checksum.get(metaData);
    blockStarts = new long[blocks.length];
    firstRows = new long[blocks.length];
    long startPosition = dataStart;
    long row = 0;
    for (int i = 0; i < blockCount; i++) {
      BlockDescriptor b = blocks[i];
      blockStarts[i] = startPosition;
      firstRows[i] = row;
      startPosition += b.compressedSize + checksum.size();
      row += b.rowCount;
    }
    this.blocks = blocks;
  }

}