/*
 * 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.mahout.math;

import com.google.common.base.Charsets;
import org.junit.Assert;
import org.junit.Test;

import java.io.UnsupportedEncodingException;

public class MurmurHashTest extends org.apache.mahout.math.MahoutTestCase {

  @Test
  public void testForLotsOfChange64() throws UnsupportedEncodingException {
    long h1 = MurmurHash.hash64A("abc".getBytes(Charsets.UTF_8), 0);
    long h2 = MurmurHash.hash64A("abc ".getBytes(Charsets.UTF_8), 0);
    int flipCount = Long.bitCount(h1 ^ h2);
    Assert.assertTrue("Small changes should result in lots of bit flips, only found " + flipCount, flipCount > 25);
  }

  @Test
  public void testHash64() {
    // test data generated by running MurmurHash2_64.cpp
    Assert.assertEquals(0x9cc9c33498a95efbL, MurmurHash.hash64A("abc".getBytes(Charsets.UTF_8), 0));
    Assert.assertEquals(0xd2c8c9b470122bddL, MurmurHash.hash64A("abc def ghi jkl ".getBytes(Charsets.UTF_8), 0));
    Assert.assertEquals(0xcd37895736a81cbcL, MurmurHash.hash64A("abc def ghi jkl moreGoo".getBytes(Charsets.UTF_8), 0));
  }

  @Test
  public void testForLotsOfChange32() throws UnsupportedEncodingException {
    int h1 = MurmurHash.hash("abc".getBytes(Charsets.UTF_8), 0);
    int h2 = MurmurHash.hash("abc ".getBytes(Charsets.UTF_8), 0);
    int flipCount = Integer.bitCount(h1 ^ h2);
    Assert.assertTrue("Small changes should result in lots of bit flips, only found " + flipCount, flipCount > 14);
  }

  // tests lifted from http://dmy999.com/article/50/murmurhash-2-java-port
  // code was marked with this notice:
  // released to the public domain - dmy999@gmail.com

  // expected values are generated from the output of a C driver that
  // ran against the same input

  @Test
  public void testChangingSeed() {
    // use a fixed key
    byte[] key = {0x4E, (byte) 0xE3, (byte) 0x91, 0x00, 0x10, (byte) 0x8F, (byte) 0xFF};

    int[] expected = {0xeef8be32, 0x8109dec6, 0x9aaf4192, 0xc1bcaf1c,
      0x821d2ce4, 0xd45ed1df, 0x6c0357a7, 0x21d4e845,
      0xfa97db50, 0x2f1985c8, 0x5d69782a, 0x0d6e4b85,
      0xe7d9cf6b, 0x337e6b49, 0xe1606944, 0xccc18ae8};

    for (int i = 0; i < expected.length; i++) {
      int expectedHash = expected[i];
      int hash = MurmurHash.hash(key, i);
      Assert.assertEquals("i = " + i, expectedHash, hash);
    }
  }

  @Test
  public void testChangingKey() {
    byte[] key = new byte[133];

    int[] expected = {0xd743ae0b, 0xf1b461c6, 0xa45a6ceb, 0xdb15e003,
      0x877721a4, 0xc30465f1, 0xfb658ba4, 0x1adf93b2,
      0xe40a7931, 0x3da52db0, 0xbf523511, 0x1efaf273,
      0xe628c1dd, 0x9a0344df, 0x901c99fc, 0x5ae1aa44};
    for (int i = 0; i < 16; i++) {
      // keep seed constant, generate a known key pattern
      setKey(key, i);
      int expectedHash = expected[i];
      int hash = MurmurHash.hash(key, 0x1234ABCD);
      Assert.assertEquals("i = " + i, expectedHash, hash);
    }
  }

  @Test
  public void testChangingKeyLength() {
    int[] expected = {0xa0c72f8e, 0x29c2f97e, 0x00ca8bba, 0x88387876,
      0xe203ce49, 0x58d75952, 0xab84febe, 0x98153c65,
      0xcbb38375, 0x6ea1a28b, 0x9afa8f55, 0xfb890eb6,
      0x9516cc49, 0x6408a8eb, 0xbb12d3e6, 0x00fb7519};
    // vary the key and the length
    for (int i = 0; i < 16; i++) {
      byte[] key = new byte[i];
      setKey(key, i);
      int expectedHash = expected[i];
      int hash = MurmurHash.hash(key, 0x7870AAFF);
      Assert.assertEquals("i = " + i, expectedHash, hash);
    }
  }

  /**
   * Fill a key with a known pattern (incrementing numbers)
   */
  private static void setKey(byte[] key, int start) {
    for (int i = 0; i < key.length; i++) {
      key[i] = (byte) ((start + i) & 0xFF);
    }
  }


}