/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed 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 com.google.common.hash;

import static com.google.common.base.Preconditions.checkArgument;

import com.google.common.math.LongMath;
import com.google.common.primitives.Ints;
import com.google.common.primitives.Longs;
import java.math.RoundingMode;
import java.util.Arrays;
import java.util.concurrent.atomic.AtomicLongArray;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Collections of strategies of generating the k * log(M) bits required for an element to be mapped
 * to a BloomFilter of M bits and k hash functions. These strategies are part of the serialized form
 * of the Bloom filters that use them, thus they must be preserved as is (no updates allowed, only
 * introduction of new versions).
 *
 * <p>Important: the order of the constants cannot change, and they cannot be deleted - we depend on
 * their ordinal for BloomFilter serialization.
 *
 * @author Dimitris Andreou
 * @author Kurt Alfred Kluever
 */
enum BloomFilterStrategies implements BloomFilter.Strategy {
  /**
   * See "Less Hashing, Same Performance: Building a Better Bloom Filter" by Adam Kirsch and Michael
   * Mitzenmacher. The paper argues that this trick doesn't significantly deteriorate the
   * performance of a Bloom filter (yet only needs two 32bit hash functions).
   */
  MURMUR128_MITZ_32() {
    @Override
    public <T> boolean put(
        T object, Funnel<? super T> funnel, int numHashFunctions, LockFreeBitArray bits) {
      long bitSize = bits.bitSize();
      long hash64 = Hashing.murmur3_128().hashObject(object, funnel).asLong();
      int hash1 = (int) hash64;
      int hash2 = (int) (hash64 >>> 32);

      boolean bitsChanged = false;
      for (int i = 1; i <= numHashFunctions; i++) {
        int combinedHash = hash1 + (i * hash2);
        // Flip all the bits if it's negative (guaranteed positive number)
        if (combinedHash < 0) {
          combinedHash = ~combinedHash;
        }
        bitsChanged |= bits.set(combinedHash % bitSize);
      }
      return bitsChanged;
    }

    @Override
    public <T> boolean mightContain(
        T object, Funnel<? super T> funnel, int numHashFunctions, LockFreeBitArray bits) {
      long bitSize = bits.bitSize();
      long hash64 = Hashing.murmur3_128().hashObject(object, funnel).asLong();
      int hash1 = (int) hash64;
      int hash2 = (int) (hash64 >>> 32);

      for (int i = 1; i <= numHashFunctions; i++) {
        int combinedHash = hash1 + (i * hash2);
        // Flip all the bits if it's negative (guaranteed positive number)
        if (combinedHash < 0) {
          combinedHash = ~combinedHash;
        }
        if (!bits.get(combinedHash % bitSize)) {
          return false;
        }
      }
      return true;
    }
  },
  /**
   * This strategy uses all 128 bits of {@link Hashing#murmur3_128} when hashing. It looks different
   * than the implementation in MURMUR128_MITZ_32 because we're avoiding the multiplication in the
   * loop and doing a (much simpler) += hash2. We're also changing the index to a positive number by
   * AND'ing with Long.MAX_VALUE instead of flipping the bits.
   */
  MURMUR128_MITZ_64() {
    @Override
    public <T> boolean put(
        T object, Funnel<? super T> funnel, int numHashFunctions, LockFreeBitArray bits) {
      long bitSize = bits.bitSize();
      byte[] bytes = Hashing.murmur3_128().hashObject(object, funnel).getBytesInternal();
      long hash1 = lowerEight(bytes);
      long hash2 = upperEight(bytes);

      boolean bitsChanged = false;
      long combinedHash = hash1;
      for (int i = 0; i < numHashFunctions; i++) {
        // Make the combined hash positive and indexable
        bitsChanged |= bits.set((combinedHash & Long.MAX_VALUE) % bitSize);
        combinedHash += hash2;
      }
      return bitsChanged;
    }

    @Override
    public <T> boolean mightContain(
        T object, Funnel<? super T> funnel, int numHashFunctions, LockFreeBitArray bits) {
      long bitSize = bits.bitSize();
      byte[] bytes = Hashing.murmur3_128().hashObject(object, funnel).getBytesInternal();
      long hash1 = lowerEight(bytes);
      long hash2 = upperEight(bytes);

      long combinedHash = hash1;
      for (int i = 0; i < numHashFunctions; i++) {
        // Make the combined hash positive and indexable
        if (!bits.get((combinedHash & Long.MAX_VALUE) % bitSize)) {
          return false;
        }
        combinedHash += hash2;
      }
      return true;
    }

    private /* static */ long lowerEight(byte[] bytes) {
      return Longs.fromBytes(
          bytes[7], bytes[6], bytes[5], bytes[4], bytes[3], bytes[2], bytes[1], bytes[0]);
    }

    private /* static */ long upperEight(byte[] bytes) {
      return Longs.fromBytes(
          bytes[15], bytes[14], bytes[13], bytes[12], bytes[11], bytes[10], bytes[9], bytes[8]);
    }
  };

  /**
   * Models a lock-free array of bits.
   *
   * <p>We use this instead of java.util.BitSet because we need access to the array of longs and we
   * need compare-and-swap.
   */
  static final class LockFreeBitArray {
    private static final int LONG_ADDRESSABLE_BITS = 6;
    final AtomicLongArray data;
    private final LongAddable bitCount;

    LockFreeBitArray(long bits) {
      this(new long[Ints.checkedCast(LongMath.divide(bits, 64, RoundingMode.CEILING))]);
    }

    // Used by serialization
    LockFreeBitArray(long[] data) {
      checkArgument(data.length > 0, "data length is zero!");
      this.data = new AtomicLongArray(data);
      this.bitCount = LongAddables.create();
      long bitCount = 0;
      for (long value : data) {
        bitCount += Long.bitCount(value);
      }
      this.bitCount.add(bitCount);
    }

    /** Returns true if the bit changed value. */
    boolean set(long bitIndex) {
      if (get(bitIndex)) {
        return false;
      }

      int longIndex = (int) (bitIndex >>> LONG_ADDRESSABLE_BITS);
      long mask = 1L << bitIndex; // only cares about low 6 bits of bitIndex

      long oldValue;
      long newValue;
      do {
        oldValue = data.get(longIndex);
        newValue = oldValue | mask;
        if (oldValue == newValue) {
          return false;
        }
      } while (!data.compareAndSet(longIndex, oldValue, newValue));

      // We turned the bit on, so increment bitCount.
      bitCount.increment();
      return true;
    }

    boolean get(long bitIndex) {
      return (data.get((int) (bitIndex >>> 6)) & (1L << bitIndex)) != 0;
    }

    /**
     * Careful here: if threads are mutating the atomicLongArray while this method is executing, the
     * final long[] will be a "rolling snapshot" of the state of the bit array. This is usually good
     * enough, but should be kept in mind.
     */
    public static long[] toPlainArray(AtomicLongArray atomicLongArray) {
      long[] array = new long[atomicLongArray.length()];
      for (int i = 0; i < array.length; ++i) {
        array[i] = atomicLongArray.get(i);
      }
      return array;
    }

    /** Number of bits */
    long bitSize() {
      return (long) data.length() * Long.SIZE;
    }

    /**
     * Number of set bits (1s).
     *
     * <p>Note that because of concurrent set calls and uses of atomics, this bitCount is a (very)
     * close *estimate* of the actual number of bits set. It's not possible to do better than an
     * estimate without locking. Note that the number, if not exactly accurate, is *always*
     * underestimating, never overestimating.
     */
    long bitCount() {
      return bitCount.sum();
    }

    LockFreeBitArray copy() {
      return new LockFreeBitArray(toPlainArray(data));
    }

    /**
     * Combines the two BitArrays using bitwise OR.
     *
     * <p>NOTE: Because of the use of atomics, if the other LockFreeBitArray is being mutated while
     * this operation is executing, not all of those new 1's may be set in the final state of this
     * LockFreeBitArray. The ONLY guarantee provided is that all the bits that were set in the other
     * LockFreeBitArray at the start of this method will be set in this LockFreeBitArray at the end
     * of this method.
     */
    void putAll(LockFreeBitArray other) {
      checkArgument(
          data.length() == other.data.length(),
          "BitArrays must be of equal length (%s != %s)",
          data.length(),
          other.data.length());
      for (int i = 0; i < data.length(); i++) {
        long otherLong = other.data.get(i);

        long ourLongOld;
        long ourLongNew;
        boolean changedAnyBits = true;
        do {
          ourLongOld = data.get(i);
          ourLongNew = ourLongOld | otherLong;
          if (ourLongOld == ourLongNew) {
            changedAnyBits = false;
            break;
          }
        } while (!data.compareAndSet(i, ourLongOld, ourLongNew));

        if (changedAnyBits) {
          int bitsAdded = Long.bitCount(ourLongNew) - Long.bitCount(ourLongOld);
          bitCount.add(bitsAdded);
        }
      }
    }

    @Override
    public boolean equals(@Nullable Object o) {
      if (o instanceof LockFreeBitArray) {
        LockFreeBitArray lockFreeBitArray = (LockFreeBitArray) o;
        // TODO(lowasser): avoid allocation here
        return Arrays.equals(toPlainArray(data), toPlainArray(lockFreeBitArray.data));
      }
      return false;
    }

    @Override
    public int hashCode() {
      // TODO(lowasser): avoid allocation here
      return Arrays.hashCode(toPlainArray(data));
    }
  }
}
