//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
//  This source code is licensed under both the GPLv2 (found in the
//  COPYING file in the root directory) and Apache 2.0 License
//  (found in the LICENSE.Apache file in the root directory).
//
#include "monitoring/histogram.h"

#include <cmath>

#include "monitoring/histogram_windowing.h"
#include "rocksdb/system_clock.h"
#include "test_util/mock_time_env.h"
#include "test_util/testharness.h"
#include "util/random.h"

namespace ROCKSDB_NAMESPACE {

class HistogramTest : public testing::Test {};

namespace {
const double kIota = 0.1;
const HistogramBucketMapper bucketMapper;
std::shared_ptr<MockSystemClock> clock =
    std::make_shared<MockSystemClock>(SystemClock::Default());
}  // namespace

void PopulateHistogram(Histogram& histogram, uint64_t low, uint64_t high,
                       uint64_t loop = 1) {
  Random rnd(test::RandomSeed());
  for (; loop > 0; loop--) {
    for (uint64_t i = low; i <= high; i++) {
      histogram.Add(i);
      // sleep a random microseconds [0-10)
      clock->SleepForMicroseconds(rnd.Uniform(10));
    }
  }
  // make sure each data population at least take some time
  clock->SleepForMicroseconds(1);
}

void BasicOperation(Histogram& histogram) {
  PopulateHistogram(histogram, 1, 110, 10);  // fill up to bucket [70, 110)

  HistogramData data;
  histogram.Data(&data);

  ASSERT_LE(fabs(histogram.Percentile(100.0) - 110.0), kIota);
  ASSERT_LE(fabs(data.percentile99 - 108.9), kIota);  // 99 * 110 / 100
  ASSERT_LE(fabs(data.percentile95 - 104.5), kIota);  // 95 * 110 / 100
  ASSERT_LE(fabs(data.median - 55.0), kIota);         // 50 * 110 / 100
  ASSERT_EQ(data.average, 55.5);                      // (1 + 110) / 2
}

void MergeHistogram(Histogram& histogram, Histogram& other) {
  PopulateHistogram(histogram, 1, 100);
  PopulateHistogram(other, 101, 250);
  histogram.Merge(other);

  HistogramData data;
  histogram.Data(&data);

  ASSERT_LE(fabs(histogram.Percentile(100.0) - 250.0), kIota);
  ASSERT_LE(fabs(data.percentile99 - 247.5), kIota);  // 99 * 250 / 100
  ASSERT_LE(fabs(data.percentile95 - 237.5), kIota);  // 95 * 250 / 100
  ASSERT_LE(fabs(data.median - 125.0), kIota);        // 50 * 250 / 100
  ASSERT_EQ(data.average, 125.5);                     // (1 + 250) / 2
}

void EmptyHistogram(Histogram& histogram) {
  ASSERT_EQ(histogram.min(), bucketMapper.LastValue());
  ASSERT_EQ(histogram.max(), 0);
  ASSERT_EQ(histogram.num(), 0);
  ASSERT_EQ(histogram.Median(), 0.0);
  ASSERT_EQ(histogram.Percentile(85.0), 0.0);
  ASSERT_EQ(histogram.Average(), 0.0);
  ASSERT_EQ(histogram.StandardDeviation(), 0.0);
}

void ClearHistogram(Histogram& histogram) {
  for (uint64_t i = 1; i <= 100; i++) {
    histogram.Add(i);
  }
  histogram.Clear();
  ASSERT_TRUE(histogram.Empty());
  ASSERT_EQ(histogram.Median(), 0);
  ASSERT_EQ(histogram.Percentile(85.0), 0);
  ASSERT_EQ(histogram.Average(), 0);
}

TEST_F(HistogramTest, BasicOperation) {
  HistogramImpl histogram;
  BasicOperation(histogram);

  HistogramWindowingImpl histogramWindowing;
  BasicOperation(histogramWindowing);
}

TEST_F(HistogramTest, BoundaryValue) {
  HistogramImpl histogram;
  // - both should be in [0, 1] bucket because we place values on bucket
  //   boundaries in the lower bucket.
  // - all points are in [0, 1] bucket, so p50 will be 0.5
  // - the test cannot be written with a single point since histogram won't
  //   report percentiles lower than the min or greater than the max.
  histogram.Add(0);
  histogram.Add(1);

  ASSERT_LE(fabs(histogram.Percentile(50.0) - 0.5), kIota);
}

TEST_F(HistogramTest, MergeHistogram) {
  HistogramImpl histogram;
  HistogramImpl other;
  MergeHistogram(histogram, other);

  HistogramWindowingImpl histogramWindowing;
  HistogramWindowingImpl otherWindowing;
  MergeHistogram(histogramWindowing, otherWindowing);
}

TEST_F(HistogramTest, EmptyHistogram) {
  HistogramImpl histogram;
  EmptyHistogram(histogram);

  HistogramWindowingImpl histogramWindowing;
  EmptyHistogram(histogramWindowing);
}

TEST_F(HistogramTest, ClearHistogram) {
  HistogramImpl histogram;
  ClearHistogram(histogram);

  HistogramWindowingImpl histogramWindowing;
  ClearHistogram(histogramWindowing);
}

TEST_F(HistogramTest, HistogramWindowingExpire) {
  uint64_t num_windows = 3;
  int micros_per_window = 1000000;
  uint64_t min_num_per_window = 0;

  HistogramWindowingImpl histogramWindowing(num_windows, micros_per_window,
                                            min_num_per_window);
  histogramWindowing.TEST_UpdateClock(clock);
  PopulateHistogram(histogramWindowing, 1, 1, 100);
  clock->SleepForMicroseconds(micros_per_window);
  ASSERT_EQ(histogramWindowing.num(), 100);
  ASSERT_EQ(histogramWindowing.min(), 1);
  ASSERT_EQ(histogramWindowing.max(), 1);
  ASSERT_EQ(histogramWindowing.Average(), 1.0);
  ASSERT_EQ(histogramWindowing.StandardDeviation(), 0.0);

  PopulateHistogram(histogramWindowing, 2, 2, 100);
  clock->SleepForMicroseconds(micros_per_window);
  ASSERT_EQ(histogramWindowing.num(), 200);
  ASSERT_EQ(histogramWindowing.min(), 1);
  ASSERT_EQ(histogramWindowing.max(), 2);
  ASSERT_EQ(histogramWindowing.Average(), 1.5);
  ASSERT_GT(histogramWindowing.StandardDeviation(), 0.0);

  PopulateHistogram(histogramWindowing, 3, 3, 100);
  clock->SleepForMicroseconds(micros_per_window);
  ASSERT_EQ(histogramWindowing.num(), 300);
  ASSERT_EQ(histogramWindowing.min(), 1);
  ASSERT_EQ(histogramWindowing.max(), 3);
  ASSERT_EQ(histogramWindowing.Average(), 2.0);
  ASSERT_GT(histogramWindowing.StandardDeviation(), 0.0);

  // dropping oldest window with value 1, remaining 2 ~ 4
  PopulateHistogram(histogramWindowing, 4, 4, 100);
  clock->SleepForMicroseconds(micros_per_window);
  ASSERT_EQ(histogramWindowing.num(), 300);
  ASSERT_EQ(histogramWindowing.min(), 2);
  ASSERT_EQ(histogramWindowing.max(), 4);
  ASSERT_EQ(histogramWindowing.Average(), 3.0);
  ASSERT_GT(histogramWindowing.StandardDeviation(), 0.0);

  // dropping oldest window with value 2, remaining 3 ~ 5
  PopulateHistogram(histogramWindowing, 5, 5, 100);
  clock->SleepForMicroseconds(micros_per_window);
  ASSERT_EQ(histogramWindowing.num(), 300);
  ASSERT_EQ(histogramWindowing.min(), 3);
  ASSERT_EQ(histogramWindowing.max(), 5);
  ASSERT_EQ(histogramWindowing.Average(), 4.0);
  ASSERT_GT(histogramWindowing.StandardDeviation(), 0.0);
}

TEST_F(HistogramTest, HistogramWindowingMerge) {
  uint64_t num_windows = 3;
  int micros_per_window = 1000000;
  uint64_t min_num_per_window = 0;

  HistogramWindowingImpl histogramWindowing(num_windows, micros_per_window,
                                            min_num_per_window);
  HistogramWindowingImpl otherWindowing(num_windows, micros_per_window,
                                        min_num_per_window);
  histogramWindowing.TEST_UpdateClock(clock);
  otherWindowing.TEST_UpdateClock(clock);

  PopulateHistogram(histogramWindowing, 1, 1, 100);
  PopulateHistogram(otherWindowing, 1, 1, 100);
  clock->SleepForMicroseconds(micros_per_window);

  PopulateHistogram(histogramWindowing, 2, 2, 100);
  PopulateHistogram(otherWindowing, 2, 2, 100);
  clock->SleepForMicroseconds(micros_per_window);

  PopulateHistogram(histogramWindowing, 3, 3, 100);
  PopulateHistogram(otherWindowing, 3, 3, 100);
  clock->SleepForMicroseconds(micros_per_window);

  histogramWindowing.Merge(otherWindowing);
  ASSERT_EQ(histogramWindowing.num(), 600);
  ASSERT_EQ(histogramWindowing.min(), 1);
  ASSERT_EQ(histogramWindowing.max(), 3);
  ASSERT_EQ(histogramWindowing.Average(), 2.0);

  // dropping oldest window with value 1, remaining 2 ~ 4
  PopulateHistogram(histogramWindowing, 4, 4, 100);
  clock->SleepForMicroseconds(micros_per_window);
  ASSERT_EQ(histogramWindowing.num(), 500);
  ASSERT_EQ(histogramWindowing.min(), 2);
  ASSERT_EQ(histogramWindowing.max(), 4);

  // dropping oldest window with value 2, remaining 3 ~ 5
  PopulateHistogram(histogramWindowing, 5, 5, 100);
  clock->SleepForMicroseconds(micros_per_window);
  ASSERT_EQ(histogramWindowing.num(), 400);
  ASSERT_EQ(histogramWindowing.min(), 3);
  ASSERT_EQ(histogramWindowing.max(), 5);
}

TEST_F(HistogramTest, LargeStandardDeviation) {
  HistogramImpl histogram;
  PopulateHistogram(histogram, 1, 1000000);
  ASSERT_LT(fabs(histogram.StandardDeviation() - 288675), 1);
}

TEST_F(HistogramTest, LostUpdateStandardDeviation) {
  HistogramImpl histogram;
  PopulateHistogram(histogram, 100, 100, 100);
  // Simulate a possible lost update (since they are not atomic)
  histogram.TEST_GetStats().sum_squares_ -= 10000;
  // Ideally zero, but should never be negative or NaN
  ASSERT_GE(histogram.StandardDeviation(), 0.0);
}

}  // namespace ROCKSDB_NAMESPACE

int main(int argc, char** argv) {
  ROCKSDB_NAMESPACE::port::InstallStackTraceHandler();
  ::testing::InitGoogleTest(&argc, argv);
  return RUN_ALL_TESTS();
}
