/*

 * Copyright (C) 2023 The Android Open Source 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.

 */

#ifndef SRC_TRACING_SERVICE_HISTOGRAM_H_

#define SRC_TRACING_SERVICE_HISTOGRAM_H_

#include <stddef.h>

#include <stdint.h>

#include <limits>

#include "perfetto/base/logging.h"

namespace perfetto {

using HistValue = int64_t;

// Usage:

// Histogram<10, 100, 1000> h;  // A histogram with 3 + 1 (overflow) bucket.

// h.Add(value);

// h.GetBucketSum(0);  // Returns SUM(x) for 0 < x <= 10

// h.GetBucketSum(1);  // Returns SUM(x) for 10 < x <= 100

// h.GetBucketSum(2);  // Returns SUM(x) for 100 < x <= 1000

// h.GetBucketSum(3);  // Returns SUM(x) for x > 1000

// Likewise h.GetBucketCount(x) returns the COUNT(x).

template <HistValue... thresholds>

class Histogram {

 public:

  // 1+ is for the overflow bucket (anything > the last threshold).

  static constexpr size_t kNumBuckets = 1 + sizeof...(thresholds);

  void Add(HistValue value) {

    size_t bucket = BucketForValue(value);

    bucket_sum_[bucket] += value;

    ++bucket_count_[bucket];

  }

  static constexpr size_t num_buckets() { return kNumBuckets; }

  HistValue GetBucketThres(size_t n) const {

    PERFETTO_DCHECK(n < kNumBuckets);

    return bucket_thres_[n];

  }

  uint64_t GetBucketCount(size_t n) const {

    PERFETTO_DCHECK(n < kNumBuckets);

    return bucket_count_[n];

  }

  HistValue GetBucketSum(size_t n) const {

    PERFETTO_DCHECK(n < kNumBuckets);

    return bucket_sum_[n];

  }

  void Merge(const Histogram& other) {

    for (size_t i = 0; i < kNumBuckets; ++i) {

      bucket_sum_[i] += other.bucket_sum_[i];

      bucket_count_[i] += other.bucket_count_[i];

    }

  }

 private:

  static size_t BucketForValue(HistValue value) {

    for (size_t i = 0; i < kNumBuckets - 1; i++) {

      if (value <= bucket_thres_[i])

        return i;

    }

    return kNumBuckets - 1;

  }

  static constexpr HistValue bucket_thres_[kNumBuckets]{

      thresholds..., std::numeric_limits<HistValue>::max()};

  HistValue bucket_sum_[kNumBuckets]{};

  uint64_t bucket_count_[kNumBuckets]{};

};

}  // namespace perfetto

#endif  // SRC_TRACING_SERVICE_HISTOGRAM_H_