/*
 * Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
 * Use of this file is governed by the BSD 3-clause license that
 * can be found in the LICENSE.txt file in the project root.
 */

class MurmurHash {
  static final int DEFAULT_SEED = 0;

  /// Initialize the hash using the specified [seed].
  ///
  /// @param seed the seed
  /// @return the intermediate hash value
  static int initialize([int seed]) {
    return seed ?? DEFAULT_SEED;
  }

  /// Update the intermediate hash value for the next input [value].
  ///
  /// @param hash the intermediate hash value
  /// @param value the value to add to the current hash
  /// @return the updated intermediate hash value
  static int update(int hash, [value]) {
    final c1 = 0xCC9E2D51;
    final c2 = 0x1B873593;
    final r1 = 15;
    final r2 = 13;
    final m = 5;
    final n = 0xE6546B64;

    var k = value is int ? value : value?.hashCode ?? 0;

    k = k * c1;
    k = (k << r1) | (k >> (32 - r1));
    k = k * c2;

    hash = hash ^ k;
    hash = (hash << r2) | (hash >> (32 - r2));
    hash = hash * m + n;

    return hash;
  }

  /// Apply the final computation steps to the intermediate value [hash]
  /// to form the final result of the MurmurHash 3 hash function.
  ///
  /// @param hash the intermediate hash value
  /// @param numberOfWords the number of integer values added to the hash
  /// @return the final hash result
  static int finish(int hash, int numberOfWords) {
    hash = hash ^ (numberOfWords * 4);
    hash = hash ^ (hash >> 16);
    hash = hash * 0x85EBCA6B;
    hash = hash ^ (hash >> 13);
    hash = hash * 0xC2B2AE35;
    hash = hash ^ (hash >> 16);
    return hash;
  }

  /// Utility function to compute the hash code of an array using the
  /// MurmurHash algorithm.
  ///
  /// @param <T> the array element type
  /// @param data the array data
  /// @param seed the seed for the MurmurHash algorithm
  /// @return the hash code of the data
  static int getHashCode<T>(List<T> data, int seed) {
    var hash = initialize(seed);

    for (var value in data) {
      hash = update(hash, value);
    }

    hash = finish(hash, data.length);
    return hash;
  }
}
