/*
 * Copyright (C) 2010 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "third_party/blink/renderer/core/timing/memory_info.h"

#include <limits>

#include "base/time/default_tick_clock.h"
#include "base/time/time.h"
#include "third_party/blink/renderer/core/frame/settings.h"
#include "third_party/blink/renderer/platform/runtime_enabled_features.h"
#include "third_party/blink/renderer/platform/wtf/math_extras.h"
#include "v8/include/v8.h"

namespace blink {

static constexpr base::TimeDelta kTwentyMinutes = base::Minutes(20);
static constexpr base::TimeDelta kFiftyMs = base::Milliseconds(50);

static void GetHeapSize(HeapInfo& info) {
  v8::HeapStatistics heap_statistics;
  v8::Isolate::GetCurrent()->GetHeapStatistics(&heap_statistics);
  info.used_js_heap_size =
      heap_statistics.used_heap_size() + heap_statistics.external_memory();
  info.total_js_heap_size =
      heap_statistics.total_physical_size() + heap_statistics.external_memory();
  info.js_heap_size_limit = heap_statistics.heap_size_limit();
}

class HeapSizeCache {
  USING_FAST_MALLOC(HeapSizeCache);

 public:
  HeapSizeCache() : clock_(base::DefaultTickClock::GetInstance()) {}
  HeapSizeCache(const HeapSizeCache&) = delete;
  HeapSizeCache& operator=(const HeapSizeCache&) = delete;

  void GetCachedHeapSize(HeapInfo& info, MemoryInfo::Precision precision) {
    MaybeUpdate(precision);
    info = info_;
  }

  static HeapSizeCache& ForCurrentThread() {
    thread_local HeapSizeCache heap_size_cache;
    return heap_size_cache;
  }

  void SetTickClockForTesting(const base::TickClock* clock) { clock_ = clock; }
  void ResetLastUpdateTimeForTesting() { last_update_time_ = std::nullopt; }

 private:
  void MaybeUpdate(MemoryInfo::Precision precision) {
    // We rate-limit queries to once every twenty minutes in the Bucketized case
    // to make it more difficult for attackers to compare memory usage before
    // and after some event. We limit to once every 50 ms in the Precise case to
    // avoid exposing precise GC timings.
    base::TimeTicks now = clock_->NowTicks();
    base::TimeDelta delta_allowed =
        precision == MemoryInfo::Precision::kBucketized ? kTwentyMinutes
                                                        : kFiftyMs;
    if (!last_update_time_.has_value() ||
        now - last_update_time_.value() >= delta_allowed) {
      Update(precision);
      last_update_time_ = now;
    }
  }

  void Update(MemoryInfo::Precision precision) {
    GetHeapSize(info_);
    if (precision == MemoryInfo::Precision::kPrecise)
      return;

    info_.used_js_heap_size = QuantizeMemorySize(info_.used_js_heap_size);
    info_.total_js_heap_size = QuantizeMemorySize(info_.total_js_heap_size);
    info_.js_heap_size_limit = QuantizeMemorySize(info_.js_heap_size_limit);
  }

  std::optional<base::TimeTicks> last_update_time_;
  const base::TickClock* clock_;

  HeapInfo info_;
};

// We quantize the sizes to make it more difficult for an attacker to see
// precise impact of operations on memory. The values are used for performance
// tuning, and hence don't need to be as refined when the value is large, so we
// threshold at a list of exponentially separated buckets.
size_t QuantizeMemorySize(size_t size) {
  const int kNumberOfBuckets = 100;
  DEFINE_STATIC_LOCAL(Vector<size_t>, bucket_size_list, ());

  if (bucket_size_list.empty()) {
    bucket_size_list.resize(kNumberOfBuckets);

    float size_of_next_bucket =
        10000000.0;  // First bucket size is roughly 10M.
    const float kLargestBucketSize = 4000000000.0;  // Roughly 4GB.
    // We scale with the Nth root of the ratio, so that we use all the bucktes.
    const float scaling_factor =
        exp(log(kLargestBucketSize / size_of_next_bucket) / kNumberOfBuckets);

    size_t next_power_of_ten = static_cast<size_t>(
        pow(10, floor(log10(size_of_next_bucket)) + 1) + 0.5);
    size_t granularity =
        next_power_of_ten / 1000;  // We want 3 signficant digits.

    for (int i = 0; i < kNumberOfBuckets; ++i) {
      size_t current_bucket_size = static_cast<size_t>(size_of_next_bucket);
      bucket_size_list[i] =
          current_bucket_size - (current_bucket_size % granularity);

      size_of_next_bucket *= scaling_factor;
      if (size_of_next_bucket >= next_power_of_ten) {
        if (std::numeric_limits<size_t>::max() / 10 <= next_power_of_ten) {
          next_power_of_ten = std::numeric_limits<size_t>::max();
        } else {
          next_power_of_ten *= 10;
          granularity *= 10;
        }
      }

      // Watch out for overflow, if the range is too large for size_t.
      if (i > 0 && bucket_size_list[i] < bucket_size_list[i - 1])
        bucket_size_list[i] = std::numeric_limits<size_t>::max();
    }
  }

  for (int i = 0; i < kNumberOfBuckets; ++i) {
    if (size <= bucket_size_list[i])
      return bucket_size_list[i];
  }

  return bucket_size_list[kNumberOfBuckets - 1];
}

MemoryInfo::MemoryInfo(Precision precision) {
  // With the experimental PreciseMemoryInfoEnabled flag on, we will not
  // bucketize or cache values, regardless of the value of |precision|. When the
  // flag is off then our cache is used and |precision| determines the
  // granularity of the values and the timer of the cache we use.
  if (RuntimeEnabledFeatures::PreciseMemoryInfoEnabled())
    GetHeapSize(info_);
  else
    HeapSizeCache::ForCurrentThread().GetCachedHeapSize(info_, precision);
  // The values must have been computed, so totalJSHeapSize must be greater than
  // 0.
  DCHECK_GT(totalJSHeapSize(), 0u);
}

// static
void MemoryInfo::SetTickClockForTestingForCurrentThread(
    const base::TickClock* clock) {
  HeapSizeCache& cache = HeapSizeCache::ForCurrentThread();
  cache.SetTickClockForTesting(clock);
  cache.ResetLastUpdateTimeForTesting();
}

}  // namespace blink