/**
 * Copyright 2016 LinkedIn Corp. All rights reserved.
 *
 * 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.
 */
package com.github.ambry.utils;

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


public abstract class BloomFilter implements IFilter {
  public final IBitSet bitset;
  public final int hashCount;

  BloomFilter(int hashes, IBitSet bitset) {
    this.hashCount = hashes;
    this.bitset = bitset;
  }

  private long[] getHashBuckets(ByteBuffer key) {
    return getHashBuckets(key, hashCount, bitset.capacity());
  }

  protected abstract long[] hash(ByteBuffer b, int position, int remaining, long seed);

  // Murmur is faster than an SHA-based approach and provides as-good collision
  // resistance.  The combinatorial generation approach described in
  // https://www.eecs.harvard.edu/~michaelm/postscripts/tr-02-05.pdf
  // does prove to work in actual tests, and is obviously faster
  // than performing further iterations of murmur.
  long[] getHashBuckets(ByteBuffer b, int hashCount, long max) {
    long[] result = new long[hashCount];
    long[] hash = this.hash(b, b.position(), b.remaining(), 0L);
    for (int i = 0; i < hashCount; ++i) {
      result[i] = Math.abs((hash[0] + (long) i * hash[1]) % max);
    }
    return result;
  }

  public void add(ByteBuffer key) {
    for (long bucketIndex : getHashBuckets(key)) {
      bitset.set(bucketIndex);
    }
  }

  public boolean isPresent(ByteBuffer key) {
    for (long bucketIndex : getHashBuckets(key)) {
      if (!bitset.get(bucketIndex)) {
        return false;
      }
    }
    return true;
  }

  public void clear() {
    bitset.clear();
  }

  public void close() throws IOException {
    bitset.close();
  }
}