content: /*
   * 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.beam.sdk.io.range;
  
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkArgument;
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkNotNull;
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkState;
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Verify.verify;
  
  import java.io.Serializable;
  import java.math.BigDecimal;
  import java.math.BigInteger;
  import java.util.Arrays;
  import java.util.List;
  import java.util.Objects;
  import org.apache.beam.sdk.transforms.splittabledofn.HasDefaultTracker;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.MoreObjects;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableList;
  import org.checkerframework.checker.nullness.qual.Nullable;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * A class representing a range of {@link ByteKey ByteKeys}.
   *
   * <p>Instances of {@link ByteKeyRange} are immutable.
   *
   * <p>A {@link ByteKeyRange} enforces the restriction that its start and end keys must form a valid,
   * non-empty range {@code [startKey, endKey)} that is inclusive of the start key and exclusive of
   * the end key.
   *
   * <p>When the end key is empty, it is treated as the largest possible key.
   *
   * <h3>Interpreting {@link ByteKey} in a {@link ByteKeyRange}</h3>
   *
   * <p>The primary role of {@link ByteKeyRange} is to provide functionality for {@link
   * #estimateFractionForKey(ByteKey)}, {@link #interpolateKey(double)}, and {@link #split(int)}.
   *
   * <p>{@link ByteKeyRange} implements these features by treating a {@link ByteKey}'s underlying
   * {@code byte[]} as the binary expansion of floating point numbers in the range {@code [0.0, 1.0]}.
   * For example, the keys {@code ByteKey.of(0x80)}, {@code ByteKey.of(0xc0)}, and {@code
   * ByteKey.of(0xe0)} are interpreted as {@code 0.5}, {@code 0.75}, and {@code 0.875} respectively.
   * The empty {@code ByteKey.EMPTY} is interpreted as {@code 0.0} when used as the start of a range
   * and {@code 1.0} when used as the end key.
   *
   * <p>Key interpolation, fraction estimation, and range splitting are all interpreted in these
   * floating-point semantics. See the respective implementations for further details. <b>Note:</b>
   * the underlying implementations of these functions use {@link BigInteger} and {@link BigDecimal},
   * so they can be slow and should not be called in hot loops. Dynamic work rebalancing will only
   * invoke these functions during periodic control operations, so they are not called on the critical
   * path.
   *
   * @see ByteKey
   */
  public final class ByteKeyRange
      implements Serializable,
          HasDefaultTracker<
              ByteKeyRange, org.apache.beam.sdk.transforms.splittabledofn.ByteKeyRangeTracker> {
  
    private static final Logger LOG = LoggerFactory.getLogger(ByteKeyRange.class);
  
    /** The range of all keys, with empty start and end keys. */
    public static final ByteKeyRange ALL_KEYS = ByteKeyRange.of(ByteKey.EMPTY, ByteKey.EMPTY);
  
    /**
     * Creates a new {@link ByteKeyRange} with the given start and end keys.
     *
     * <p>Note that if {@code endKey} is empty, it is treated as the largest possible key.
     *
     * @see ByteKeyRange
     * @throws IllegalArgumentException if {@code endKey} is less than or equal to {@code startKey},
     *     unless {@code endKey} is empty indicating the maximum possible {@link ByteKey}.
     */
    public static ByteKeyRange of(ByteKey startKey, ByteKey endKey) {
      return new ByteKeyRange(startKey, endKey);
    }
  
    /** Returns the {@link ByteKey} representing the lower bound of this {@link ByteKeyRange}. */
    public ByteKey getStartKey() {
      return startKey;
    }
  
    /**
     * Returns the {@link ByteKey} representing the upper bound of this {@link ByteKeyRange}.
     *
     * <p>Note that if {@code endKey} is empty, it is treated as the largest possible key.
     */
    public ByteKey getEndKey() {
      return endKey;
    }
  
    /** Returns {@code true} if the specified {@link ByteKey} is contained within this range. */
    public Boolean containsKey(ByteKey key) {
      return key.compareTo(startKey) >= 0 && endsAfterKey(key);
    }
  
    /** Returns {@code true} if the specified {@link ByteKeyRange} overlaps this range. */
    public Boolean overlaps(ByteKeyRange other) {
      // If each range starts before the other range ends, then they must overlap.
      //     { [] } -- one range inside the other   OR   { [ } ] -- partial overlap.
      return endsAfterKey(other.startKey) && other.endsAfterKey(startKey);
    }
  
    /**
     * Returns a list of up to {@code numSplits + 1} {@link ByteKey ByteKeys} in ascending order,
     * where the keys have been interpolated to form roughly equal sub-ranges of this {@link
     * ByteKeyRange}, assuming a uniform distribution of keys within this range.
     *
     * <p>The first {@link ByteKey} in the result is guaranteed to be equal to {@link #getStartKey},
     * and the last {@link ByteKey} in the result is guaranteed to be equal to {@link #getEndKey}.
     * Thus the resulting list exactly spans the same key range as this {@link ByteKeyRange}.
     *
     * <p>Note that the number of keys returned is not always equal to {@code numSplits + 1}.
     * Specifically, if this range is unsplittable (e.g., because the start and end keys are equal up
     * to padding by zero bytes), the list returned will only contain the start and end key.
     *
     * @throws IllegalArgumentException if the specified number of splits is less than 1
     * @see ByteKeyRange the ByteKeyRange class Javadoc for more information about split semantics.
     */
    public List<ByteKey> split(int numSplits) {
      checkArgument(numSplits > 0, "numSplits %s must be a positive integer", numSplits);
  
      try {
        ImmutableList.Builder<ByteKey> ret = ImmutableList.builder();
        ret.add(startKey);
        for (int i = 1; i < numSplits; ++i) {
          ret.add(interpolateKey(i / (double) numSplits));
        }
        ret.add(endKey);
        return ret.build();
      } catch (IllegalStateException e) {
        // The range is not splittable -- just return
        return ImmutableList.of(startKey, endKey);
      }
    }
  
    /**
     * Returns the fraction of this range {@code [startKey, endKey)} that is in the interval {@code
     * [startKey, key)}.
     *
     * @throws IllegalArgumentException if {@code key} does not fall within this range
     * @see ByteKeyRange the ByteKeyRange class Javadoc for more information about fraction semantics.
     */
    public double estimateFractionForKey(ByteKey key) {
      checkNotNull(key, "key");
      checkArgument(!key.isEmpty(), "Cannot compute fraction for an empty key");
      checkArgument(
          key.compareTo(startKey) >= 0, "Expected key %s >= range start key %s", key, startKey);
  
      if (key.equals(endKey)) {
        return 1.0;
      }
      checkArgument(containsKey(key), "Cannot compute fraction for %s outside this %s", key, this);
  
      byte[] startBytes = startKey.getBytes();
      byte[] endBytes = endKey.getBytes();
      byte[] keyBytes = key.getBytes();
      // If the endKey is unspecified, add a leading 1 byte to it and a leading 0 byte to all other
      // keys, to get a concrete least upper bound for the desired range.
      if (endKey.isEmpty()) {
        startBytes = addHeadByte(startBytes, (byte) 0);
        endBytes = addHeadByte(endBytes, (byte) 1);
        keyBytes = addHeadByte(keyBytes, (byte) 0);
      }
  
      // Pad to the longest of all 3 keys.
      int paddedKeyLength = Math.max(Math.max(startBytes.length, endBytes.length), keyBytes.length);
      BigInteger rangeStartInt = paddedPositiveInt(startBytes, paddedKeyLength);
      BigInteger rangeEndInt = paddedPositiveInt(endBytes, paddedKeyLength);
      BigInteger keyInt = paddedPositiveInt(keyBytes, paddedKeyLength);
  
      // Keys are equal subject to padding by 0.
      BigInteger range = rangeEndInt.subtract(rangeStartInt);
      if (range.equals(BigInteger.ZERO)) {
        LOG.warn(
            "Using 0.0 as the default fraction for this near-empty range {} where start and end keys"
                + " differ only by trailing zeros.",
            this);
        return 0.0;
      }
  
      // Compute the progress (key-start)/(end-start) scaling by 2^64, dividing (which rounds),
      // and then scaling down after the division. This gives ample precision when converted to
      // double.
      BigInteger progressScaled = keyInt.subtract(rangeStartInt).shiftLeft(64);
      return progressScaled.divide(range).doubleValue() / Math.pow(2, 64);
    }
  
    /**
     * Returns a {@link ByteKey} {@code key} such that {@code [startKey, key)} represents
     * approximately the specified fraction of the range {@code [startKey, endKey)}. The interpolation
     * is computed assuming a uniform distribution of keys.
     *
     * <p>For example, given the largest possible range (defined by empty start and end keys), the
     * fraction {@code 0.5} will return the {@code ByteKey.of(0x80)}, which will also be returned for
     * ranges {@code [0x40, 0xc0)} and {@code [0x6f, 0x91)}.
     *
     * <p>The key returned will never be empty.
     *
     * @throws IllegalArgumentException if {@code fraction} is outside the range [0, 1)
     * @throws IllegalStateException if this range cannot be interpolated
     * @see ByteKeyRange the ByteKeyRange class Javadoc for more information about fraction semantics.
     */
    public ByteKey interpolateKey(double fraction) {
      checkArgument(
          fraction >= 0.0 && fraction < 1.0, "Fraction %s must be in the range [0, 1)", fraction);
      byte[] startBytes = startKey.getBytes();
      byte[] endBytes = endKey.getBytes();
      // If the endKey is unspecified, add a leading 1 byte to it and a leading 0 byte to all other
      // keys, to get a concrete least upper bound for the desired range.
      if (endKey.isEmpty()) {
        startBytes = addHeadByte(startBytes, (byte) 0);
        endBytes = addHeadByte(endBytes, (byte) 1);
      }
  
      // Pad to the longest key.
      int paddedKeyLength = Math.max(startBytes.length, endBytes.length);
      BigInteger rangeStartInt = paddedPositiveInt(startBytes, paddedKeyLength);
      BigInteger rangeEndInt = paddedPositiveInt(endBytes, paddedKeyLength);
  
      // If the keys are equal subject to padding by 0, we can't interpolate.
      BigInteger range = rangeEndInt.subtract(rangeStartInt);
      checkState(
          !range.equals(BigInteger.ZERO),
          "Refusing to interpolate for near-empty %s where start and end keys differ only by trailing"
              + " zero bytes.",
          this);
  
      // Add precision so that range is at least 53 (double mantissa length) bits long. This way, we
      // can interpolate small ranges finely, e.g., split the range key 3 to key 4 into 1024 parts.
      // We add precision to range by adding zero bytes to the end of the keys, aka shifting the
      // underlying BigInteger left by a multiple of 8 bits.
      int bytesNeeded = ((53 - range.bitLength()) + 7) / 8;
      if (bytesNeeded > 0) {
        range = range.shiftLeft(bytesNeeded * 8);
        rangeStartInt = rangeStartInt.shiftLeft(bytesNeeded * 8);
        paddedKeyLength += bytesNeeded;
      }
  
      BigInteger interpolatedOffset =
          new BigDecimal(range).multiply(BigDecimal.valueOf(fraction)).toBigInteger();
  
      int outputKeyLength = endKey.isEmpty() ? (paddedKeyLength - 1) : paddedKeyLength;
      return ByteKey.copyFrom(
          fixupHeadZeros(rangeStartInt.add(interpolatedOffset).toByteArray(), outputKeyLength));
    }
  
    /** Returns new {@link ByteKeyRange} like this one, but with the specified start key. */
    public ByteKeyRange withStartKey(ByteKey startKey) {
      return new ByteKeyRange(startKey, endKey);
    }
  
    /** Returns new {@link ByteKeyRange} like this one, but with the specified end key. */
    public ByteKeyRange withEndKey(ByteKey endKey) {
      return new ByteKeyRange(startKey, endKey);
    }
  
    ////////////////////////////////////////////////////////////////////////////////////
    private final ByteKey startKey;
    private final ByteKey endKey;
  
    private ByteKeyRange(ByteKey startKey, ByteKey endKey) {
      this.startKey = checkNotNull(startKey, "startKey");
      this.endKey = checkNotNull(endKey, "endKey");
      checkArgument(
          endKey.isEmpty() || startKey.compareTo(endKey) <= 0,
          "Start %s must be less than or equal to end %s",
          startKey,
          endKey);
    }
  
    @Override
    public String toString() {
      return MoreObjects.toStringHelper(ByteKeyRange.class)
          .add("startKey", startKey)
          .add("endKey", endKey)
          .toString();
    }
  
    @Override
    public boolean equals(@Nullable Object o) {
      if (o == this) {
        return true;
      }
      if (!(o instanceof ByteKeyRange)) {
        return false;
      }
      ByteKeyRange other = (ByteKeyRange) o;
      return Objects.equals(startKey, other.startKey) && Objects.equals(endKey, other.endKey);
    }
  
    @Override
    public int hashCode() {
      return Objects.hash(startKey, endKey);
    }
  
    /** Returns a copy of the specified array with the specified byte added at the front. */
    private static byte[] addHeadByte(byte[] array, byte b) {
      byte[] ret = new byte[array.length + 1];
      ret[0] = b;
      System.arraycopy(array, 0, ret, 1, array.length);
      return ret;
    }
  
    /**
     * Ensures the array is exactly {@code size} bytes long. Returns the input array if the condition
     * is met, otherwise either adds or removes zero bytes from the beginning of {@code array}.
     */
    private static byte[] fixupHeadZeros(byte[] array, int size) {
      int padding = size - array.length;
      if (padding == 0) {
        return array;
      }
  
      if (padding < 0) {
        // There is one zero byte at the beginning, added by BigInteger to make there be a sign
        // bit when converting to bytes.
        verify(
            padding == -1,
            "key %s: expected length %s with exactly one byte of padding, found %s",
            ByteKey.copyFrom(array),
            size,
            -padding);
        verify(
            (array[0] == 0) && ((array[1] & 0x80) == 0x80),
            "key %s: is 1 byte longer than expected, indicating BigInteger padding. Expect first byte"
                + " to be zero with set MSB in second byte.",
            ByteKey.copyFrom(array));
        return Arrays.copyOfRange(array, 1, array.length);
      }
  
      byte[] ret = new byte[size];
      System.arraycopy(array, 0, ret, padding, array.length);
      return ret;
    }
  
    /**
     * Returns {@code true} when the specified {@code key} is smaller this range's end key. The only
     * semantic change from {@code (key.compareTo(getEndKey()) < 0)} is that the empty end key is
     * treated as larger than all possible {@link ByteKey keys}.
     */
    boolean endsAfterKey(ByteKey key) {
      return endKey.isEmpty() || key.compareTo(endKey) < 0;
    }
  
    /** Builds a BigInteger out of the specified array, padded to the desired byte length. */
    private static BigInteger paddedPositiveInt(byte[] bytes, int length) {
      int bytePaddingNeeded = length - bytes.length;
      checkArgument(
          bytePaddingNeeded >= 0, "Required bytes.length %s < length %s", bytes.length, length);
      BigInteger ret = new BigInteger(1, bytes);
      return (bytePaddingNeeded == 0) ? ret : ret.shiftLeft(8 * bytePaddingNeeded);
    }
  
    @Override
    public org.apache.beam.sdk.transforms.splittabledofn.ByteKeyRangeTracker newTracker() {
      return org.apache.beam.sdk.transforms.splittabledofn.ByteKeyRangeTracker.of(this);
    }
  }
  