Assign to A/B test

Experiment.scala

import com.google.common.hash.{Hashing, HashFunction};

/**
 * Deterministic algorithm for assigning given variables to variants A or B with given probability.
 *
 * @param id The experiment's identifier
 * @param pA Probability of A (probability of B is 'pB = 1.0 - pA').
 */
class Experiment(val id: String, pA: Float) {
  /**
   * CRC32 is very fast and not significantly worse that cryptographic
   * hash functions in terms of uniformity of the outputs.
   *
   * Source michiel.buddingh.eu/distribution-of-hash-values
   */
  private val hashFunction: HashFunction = Hashing.crc32()

  private val threshold: Int = (Int.MaxValue - (4294967295L * pA)).toInt

  def isVariantA(variables: String*): Boolean = hashVariables(variables) > threshold

  protected def hashVariables(variables: Seq[String]): Int = {
    val str = s"$id:${variables.mkString(":")}"
    hashFunction.hashString(str, StandardCharsets.UTF_8).asInt()
  }
}