/*
 * 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 java.math.RoundingMode;
import java.util.Arrays;

import com.google.common.math.LongMath;
import com.google.common.primitives.Ints;
import com.google.common.primitives.Longs;

/**
 * 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).
 *
 * 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, BitArray 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, BitArray 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, BitArray 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, BitArray 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]);
		}
	};

	// Note: We use this instead of java.util.BitSet because we need access to the
	// long[] data field
	static final class BitArray {
		final long[] data;
		long bitCount;

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

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

		/** Returns true if the bit changed value. */
		boolean set(long index) {
			if (!get(index)) {
				data[(int) (index >>> 6)] |= (1L << index);
				bitCount++;
				return true;
			}
			return false;
		}

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

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

		/** Number of set bits (1s) */
		long bitCount() {
			return bitCount;
		}

		BitArray copy() {
			return new BitArray(data.clone());
		}

		/** Combines the two BitArrays using bitwise OR. */
		void putAll(BitArray array) {
			checkArgument(data.length == array.data.length, "BitArrays must be of equal length (%s != %s)", data.length,
					array.data.length);
			bitCount = 0;
			for (int i = 0; i < data.length; i++) {
				data[i] |= array.data[i];
				bitCount += Long.bitCount(data[i]);
			}
		}

		@Override
		public boolean equals(Object o) {
			if (o instanceof BitArray) {
				BitArray bitArray = (BitArray) o;
				return Arrays.equals(data, bitArray.data);
			}
			return false;
		}

		@Override
		public int hashCode() {
			return Arrays.hashCode(data);
		}
	}
}
