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/*
 * Copyright 2013-2021 The Kamon Project 
 *
 * 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 kamon
package trace

import java.util.concurrent.ThreadLocalRandom

import kamon.trace.Trace.SamplingDecision

/**
  * Sampler that uses a random number generator and a probability threshold to decide whether to trace a request or not.
  */
class RandomSampler private(probability: Double) extends Sampler {
  private val _upperBoundary = Long.MaxValue * probability
  private val _lowerBoundary = -_upperBoundary
  private val _affirmativeDecisionCounter = Sampler.Metrics.samplingDecisions("random", SamplingDecision.Sample)
  private val _negativeDecisionCounter = Sampler.Metrics.samplingDecisions("random", SamplingDecision.DoNotSample)

  override def decide(operation: Sampler.Operation): SamplingDecision = {
    val random = ThreadLocalRandom.current().nextLong()
    if(random >= _lowerBoundary && random <= _upperBoundary) {
      _affirmativeDecisionCounter.increment()
      SamplingDecision.Sample
    } else {
      _negativeDecisionCounter.increment()
      SamplingDecision.DoNotSample
    }
  }

  override def toString: String =
    s"RandomSampler(probability = $probability)"
}

object RandomSampler {

  /**
    * Creates a new RandomSampler with the provided probability. If the probability is greater than 1D it will be
    * adjusted to 1D and if it is lower than 0 it will be adjusted to 0.
    */
  def apply(probability: Double): RandomSampler = {
    val sanitizedProbability = if(probability > 1D) 1D else if (probability < 0D) 0D else probability
    new RandomSampler(sanitizedProbability)
  }

  /**
    * Creates a new RandomSampler with the provided probability. If the probability is greater than 1D it will be
    * adjusted to 1D and if it is lower than 0 it will be adjusted to 0.
    */
  def create(probability: Double): RandomSampler =
    apply(probability)
}