/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserved.

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. */

#include "ParameterUpdaterHook.h"

#include <algorithm>
#include <atomic>
#include <fstream>
#include <mutex>
#include <thread>
#include <unordered_map>
#include <vector>

#include "paddle/math/Vector.h"
#include "paddle/parameter/Parameter.h"
#include "paddle/utils/Flags.h"
#include "paddle/utils/Util.h"

namespace paddle {

/**
 * The static pruning hook
 * Static means user specify a sparsity_ratio before training started, and the
 * network will prune the parameters based on the sparsity_ratio. More details
 * can be found https://arxiv.org/pdf/1506.02626.pdf.
 */

class StaticPruningHook : public IParameterUpdaterHook {
 public:
  explicit StaticPruningHook(const ParameterUpdaterHookConfig &hookConfig)
      : initCount_(0) {
    sparsityRatio_ = hookConfig.sparsity_ratio();
  }

  static bool sortPairAscend(const std::pair<real, size_t> &pair1,
                             const std::pair<real, size_t> &pair2) {
    return pair1.first > pair2.first;
  }

  void update(Parameter *para) {
    updateThreadChecker_.check();
    auto &vec = para->getBuf(PARAMETER_GRADIENT);
    if (vec) {
      vec->dotMul(*maskVec_);
    }
  }

  void generateMask(Parameter *para) {
    VectorPtr maskTemp = Vector::create(para->getSize(), false);
    maskTemp->zeroMem();
    real *maskTempData = maskTemp->getData();
    size_t nonZeroNum = para->getSize() * (1 - sparsityRatio_);

    VectorPtr paraVec = para->getBuf(PARAMETER_VALUE);
    VectorPtr paraCpuCopy = Vector::create(para->getSize(), false);

    paraCpuCopy->copyFrom(*paraVec);
    std::vector<std::pair<real, size_t>> param;

    for (size_t i = 0; i < para->getSize(); i++)
      param.push_back(std::make_pair(fabs(paraCpuCopy->getData()[i]), i));

    std::partial_sort(
        param.begin(), param.begin() + nonZeroNum, param.end(), sortPairAscend);
    for (size_t i = 0; i < nonZeroNum; i++) maskTempData[param[i].second] = 1.0;

    // Currently just use a mask vector for hack.
    if (para->useGpu()) {
      maskVec_ = Vector::create(para->getSize(), para->useGpu());
      maskVec_->copyFrom(*maskTemp);
    } else {
      maskVec_ = maskTemp;
    }
  }

  void init(Parameter *para) {
    generateMask(para);
    size_t initCount = this->initCount_.fetch_add(1);
    CHECK_EQ(initCount, 0UL) << "Currently the StaticPruningHook must invoke "
                                "in same ParamterUpdater";
    VLOG(3) << "Initialize Parameter " << para;
    SetDevice device(para->getDeviceId());

    auto &paraVec = para->getBuf(PARAMETER_VALUE);
    paraVec->dotMul(*maskVec_);
  }

 private:
  SameThreadChecker updateThreadChecker_;
  std::atomic<size_t> initCount_;
  VectorPtr maskVec_;
  real sparsityRatio_;
};

IParameterUpdaterHook::IParameterUpdaterHook() {}

IParameterUpdaterHook::~IParameterUpdaterHook() {}

/**
 * A Hasher used by g_hooks.
 *
 * Use the independent hasher intendedly. There is a hasher in PServer for hash
 * ParameterBlock. But not to use same hasher to reduce dependency.
 *
 * May be extracted to Util.h to unify the hasher.
 */
class StringIntPairHasher {
 public:
  size_t operator()(const std::pair<std::string, int> &k) const {
    return intHasher_(strHasher_(k.first) + k.second);
  }

 private:
  std::hash<std::string> strHasher_;
  std::hash<int> intHasher_;
};

static WeakKVCache<std::pair<std::string, int>,
                   IParameterUpdaterHook,
                   StringIntPairHasher>
    g_hookCache_;

/**
 * ParameterUpdaterHook actually factory method.
 */
static IParameterUpdaterHook *createImpl(
    const ParameterUpdaterHookConfig &config) {
  auto &type = config.type();
  if (type == "pruning") {
    return new StaticPruningHook(config);
  }

  LOG(FATAL) << "Unknown Hook type:  " << type;
  return nullptr;
}

std::shared_ptr<IParameterUpdaterHook> IParameterUpdaterHook::create(
    const ParameterConfig &paramConfig, int idx) {
  std::pair<std::string, int> key = {paramConfig.name(), idx};
  return g_hookCache_.get(
      key, [&] { return createImpl(paramConfig.update_hooks(idx)); });
}

}  // namespace paddle