////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2016 ArangoDB GmbH, Cologne, Germany
///
/// 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.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Dr. Frank Celler
////////////////////////////////////////////////////////////////////////////////

#include "ApplicationFeatures/V8PlatformFeature.h"

#include "Basics/StringUtils.h"
#include "Logger/Logger.h"
#include "ProgramOptions/ProgramOptions.h"
#include "ProgramOptions/Section.h"

using namespace arangodb;
using namespace arangodb::basics;
using namespace arangodb::options;

namespace {
class ArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
 public:
  virtual void* Allocate(size_t length) override {
    void* data = AllocateUninitialized(length);
    return data == nullptr ? data : memset(data, 0, length);
  }
  virtual void* AllocateUninitialized(size_t length) override {
    return malloc(length);
  }
  virtual void Free(void* data, size_t) override { free(data); }
};
}

V8PlatformFeature::V8PlatformFeature(
    application_features::ApplicationServer* server)
    : ApplicationFeature(server, "V8Platform") {
  setOptional(true);
  requiresElevatedPrivileges(false);
  startsAfter("Logger");
}

void V8PlatformFeature::collectOptions(
    std::shared_ptr<ProgramOptions> options) {
  options->addSection("javascript", "Configure the Javascript engine");

  options->addHiddenOption("--javascript.v8-options", "options to pass to v8",
                           new VectorParameter<StringParameter>(&_v8Options));

  options->addOption("--javascript.v8-max-heap", "maximal heap size",
                     new UInt64Parameter(&_v8MaxHeap));
}

void V8PlatformFeature::validateOptions(
    std::shared_ptr<ProgramOptions> options) {
  if (!_v8Options.empty()) {
    _v8CombinedOptions = StringUtils::join(_v8Options, " ");

    if (_v8CombinedOptions == "help") {
      std::string help = "--help";
      v8::V8::SetFlagsFromString(help.c_str(), (int)help.size());
      exit(EXIT_SUCCESS);
    }
  }
}

void V8PlatformFeature::start() {
  v8::V8::InitializeICU();

  // explicit option --javascript.v8-options used
  if (!_v8CombinedOptions.empty()) {
    LOG_TOPIC(INFO, Logger::V8) << "using V8 options '" << _v8CombinedOptions
                                << "'";
    v8::V8::SetFlagsFromString(_v8CombinedOptions.c_str(),
                               (int)_v8CombinedOptions.size());
  }

#ifdef TRI_FORCE_ARMV6
  std::string const forceARMv6 = "--noenable-armv7";
  v8::V8::SetFlagsFromString(forceARMv6.c_str(), (int)forceARMv6.size());
#endif

  _platform.reset(v8::platform::CreateDefaultPlatform());
  v8::V8::InitializePlatform(_platform.get());
  v8::V8::Initialize();

  _allocator.reset(new ArrayBufferAllocator);
}

void V8PlatformFeature::unprepare() {
  v8::V8::Dispose();
  v8::V8::ShutdownPlatform();
  _platform.reset();
  _allocator.reset();
}

void gcPrologueCallback(v8::Isolate* isolate, v8::GCType type,
                        v8::GCCallbackFlags flags) {
  // if (type != v8::kGCTypeMarkSweepCompact) {
  //   return;
  // }

  v8::HeapStatistics h;
  isolate->GetHeapStatistics(&h);

  V8PlatformFeature::getIsolateData(isolate)->_heapSizeAtStart =
      h.used_heap_size();
}

void gcEpilogueCallback(v8::Isolate* isolate, v8::GCType type,
                        v8::GCCallbackFlags flags) {
  static size_t const LIMIT_ABS = 200 * 1024 * 1024;
  size_t minFreed = LIMIT_ABS / 10;

  if (type != v8::kGCTypeMarkSweepCompact) {
    minFreed = 0;
  }

  v8::HeapStatistics h;
  isolate->GetHeapStatistics(&h);

  size_t freed = 0;
  size_t heapSizeAtStop = h.used_heap_size();
  size_t heapSizeAtStart =
      V8PlatformFeature::getIsolateData(isolate)->_heapSizeAtStart;

  if (heapSizeAtStop < heapSizeAtStart) {
    freed = heapSizeAtStart - heapSizeAtStop;
  }

  size_t heapSizeLimit = h.heap_size_limit();
  size_t usedHeadSize = h.used_heap_size();
  size_t stillFree = heapSizeLimit - usedHeadSize;

  if (stillFree <= LIMIT_ABS && freed <= minFreed) {
    LOG(WARN) << "reached heap-size limit, interrupting V8 execution ("
              << "heap size limit " << heapSizeLimit << ", used "
              << usedHeadSize << ")";

    isolate->TerminateExecution();
    V8PlatformFeature::setOutOfMemory(isolate);
  }
}

v8::Isolate* V8PlatformFeature::createIsolate() {
  v8::Isolate::CreateParams createParams;
  createParams.array_buffer_allocator = _allocator.get();

  if (0 < _v8MaxHeap) {
    createParams.constraints.set_max_old_space_size(_v8MaxHeap);
  }

  auto isolate = v8::Isolate::New(createParams);
  isolate->AddGCPrologueCallback(gcPrologueCallback);
  isolate->AddGCEpilogueCallback(gcEpilogueCallback);

  _isolateData.emplace_back(new IsolateData());
  isolate->SetData(V8_INFO, _isolateData.back().get());

  return isolate;
}