#pragma once

#include <torch/serialize/archive.h>
#include <torch/types.h>
#include <torch/optim/optimizer.h>
#include <cstddef>
#include <cstdint>
#include <deque>
#include <string>
#include <vector>

namespace torch {
namespace optim {
namespace detail {
  // Utility function to save state
  template <typename DerivedOptimizerParamState>
  void serialize(
      serialize::OutputArchive& archive,
      const ska::flat_hash_map<std::string, std::unique_ptr<OptimizerParamState>>& state) {
    for (const auto& item : state) {
      serialize::OutputArchive param_state_archive(archive.compilation_unit());
      std::string tensorimpl_key = item.first;
      const DerivedOptimizerParamState& curr_state = static_cast<const DerivedOptimizerParamState&>(*(item.second.get()));
      curr_state.serialize(param_state_archive);
      archive.write(tensorimpl_key, param_state_archive);
    }
  }

  // Utility function to load state
  template <typename DerivedOptimizerParamState>
  void serialize(
      serialize::InputArchive& archive,
      ska::flat_hash_map<std::string, std::unique_ptr<OptimizerParamState>>& state) {
    std::vector<std::string> tensorimpl_keys = archive.keys();
    for (const std::string& tensorimpl_key : tensorimpl_keys) {
      serialize::InputArchive param_state_archive;
      archive.read(tensorimpl_key, param_state_archive);
      DerivedOptimizerParamState param_state;
      param_state.serialize(param_state_archive);
      state[tensorimpl_key] = std::make_unique<DerivedOptimizerParamState>(param_state);
    }
  }

  // Utility function to save param_groups
  template <typename DerivedOptimizerParamOptions>
  void serialize(
      serialize::OutputArchive& archive,
      const std::vector<OptimizerParamGroup>& param_groups) {
    archive.write("param_groups/size", torch::tensor(static_cast<int64_t>(param_groups.size())));
    for (size_t i = 0; i < param_groups.size(); i++) {
      serialize::OutputArchive param_group_archive(archive.compilation_unit());
      std::vector<Tensor> params = param_groups[i].params();
      param_group_archive.write(
          "params/size", torch::tensor(static_cast<int64_t>(params.size())));
      for (size_t index = 0; index < params.size(); index++) {
        param_group_archive.write(
            "params/" + c10::guts::to_string(index), IValue(c10::guts::to_string(params[index].unsafeGetTensorImpl())));
      }
      const DerivedOptimizerParamOptions& param_group_options = static_cast<const DerivedOptimizerParamOptions&>(param_groups[i].options());
      serialize::OutputArchive param_group_options_archive(param_group_archive.compilation_unit());
      param_group_options.serialize(param_group_options_archive);
      param_group_archive.write("options", param_group_options_archive);
      archive.write("param_groups/" + c10::guts::to_string(i), param_group_archive);
    }
  }

  // Utility function to load param_groups
  // We take as input vector of pair of string and unique_ptr to optimizer options so that we can retain the state
  // for each param by using the old tensor impl keys (saved during serialization) and map the new tensor impl keys to
  // the correct state for each param
  template <typename DerivedOptimizerParamOptions>
  void serialize(
      serialize::InputArchive& archive,
      std::vector<std::pair<std::vector<std::string>, std::unique_ptr<OptimizerOptions>>>& param_groups) {
    torch::Tensor param_groups_size_tensor;
    archive.read("param_groups/size", param_groups_size_tensor);
    const int64_t param_groups_size = param_groups_size_tensor.item<int64_t>();
    for (int64_t i = 0; i < param_groups_size; i++) {
      serialize::InputArchive param_group_archive;
      archive.read("param_groups/" + c10::guts::to_string(i), param_group_archive);
      torch::Tensor size_tensor;
      param_group_archive.read("params/size", size_tensor);
      const int64_t size = size_tensor.item<int64_t>();
      std::vector<std::string> params;
      for (int64_t index = 0; index < size; ++index) {
        IValue ivalue;
        param_group_archive.read(
          "params/" + c10::to_string(index), ivalue);
        std::string element = ivalue.toStringRef();
        params.emplace_back(element);
      }
      serialize::InputArchive param_group_options_archive;
      param_group_archive.read("options", param_group_options_archive);
      DerivedOptimizerParamOptions param_group_options;
      param_group_options.serialize(param_group_options_archive);
      param_groups.emplace_back(std::make_pair(params, std::make_unique<DerivedOptimizerParamOptions>(param_group_options)));
    }
  }
} // namespace detail


// Note: These functions are all called `serialize()` so they can be called
// inside a template where the archive type is a template type and can thus be
// passed such that the appropriate overload is selected.

/// Utility function to save a value of `int64_t` type.
void serialize(
    serialize::OutputArchive& archive,
    const std::string& key,
    const int64_t& value);

/// Utility function to load a value of `int64_t` type.
void serialize(
    serialize::InputArchive& archive,
    const std::string& key,
    int64_t& value);

/// Utility function to save a vector of step buffers.
void serialize(
    serialize::OutputArchive& archive,
    const std::string& key,
    const std::vector<int64_t>& steps);

/// Utility function to load a vector of step buffers.
void serialize(
    serialize::InputArchive& archive,
    const std::string& key,
    std::vector<int64_t>& steps);

// Utility function to save state and param_groups
template <typename DerivedOptimizerParamState, typename DerivedOptimizerParamOptions>
void serialize(
    serialize::OutputArchive& archive,
    const detail::OptimizerBase& optimizer) {
  archive.write("pytorch_version", IValue("1.5.0"));
  serialize::OutputArchive state_archive(archive.compilation_unit());
  detail::serialize<DerivedOptimizerParamState>(state_archive, optimizer.state());
  archive.write("state", state_archive);

  serialize::OutputArchive param_groups_archive(archive.compilation_unit());
  detail::serialize<DerivedOptimizerParamOptions>(param_groups_archive, optimizer.param_groups());
  archive.write("param_groups", param_groups_archive);
}

// Utility function to load state and param_groups and update state
template <typename DerivedOptimizerParamState, typename DerivedOptimizerParamOptions>
void serialize(
    serialize::InputArchive& archive,
    detail::OptimizerBase& optimizer) {

    IValue pytorch_version;
    archive.read("pytorch_version", pytorch_version);
    TORCH_INTERNAL_ASSERT(pytorch_version.toStringRef() == "1.5.0");
    serialize::InputArchive state_archive;
    archive.read("state", state_archive);
    ska::flat_hash_map<std::string, std::unique_ptr<OptimizerParamState>> saved_state;
    detail::serialize<DerivedOptimizerParamState>(state_archive, saved_state);

    serialize::InputArchive param_groups_archive;
    archive.read("param_groups", param_groups_archive);
    std::vector<std::pair<std::vector<std::string>, std::unique_ptr<OptimizerOptions>>> saved_param_groups;
    detail::serialize<DerivedOptimizerParamOptions>(param_groups_archive, saved_param_groups);

    // update state
    TORCH_CHECK(saved_param_groups.size() == optimizer.param_groups().size(), "loaded state dict has a different number of parameter groups");
    for (size_t i = 0; i < saved_param_groups.size(); i++) {
      std::vector<std::string> saved_group_keys = saved_param_groups[i].first;
      std::vector<Tensor> params = optimizer.param_groups()[i].params();
      TORCH_CHECK(saved_group_keys.size() == params.size(), "loaded state dict contains a parameter group that has a different size than the optimizer's parameter group");
      for (size_t idx = 0; idx < params.size(); idx++) {
        optimizer.state()[c10::guts::to_string(params[idx].unsafeGetTensorImpl())] = std::move(saved_state[saved_group_keys[idx]]);
      }
    }
}

/// Utility function to save a vector of buffers.
template <typename BufferContainer>
void serialize(
    serialize::OutputArchive& archive,
    const std::string& key,
    const BufferContainer& buffers) {
  archive.write(
      key + "/size", torch::tensor(static_cast<int64_t>(buffers.size())));
  for (size_t index = 0; index < buffers.size(); ++index) {
    archive.write(
        key + "/" + c10::to_string(index), buffers[index], /*is_buffer=*/true);
  }
}

/// Utility function to load a vector of buffers.
template <typename BufferContainer>
void serialize(
    serialize::InputArchive& archive,
    const std::string& key,
    BufferContainer& buffers) {
  buffers.clear();
  torch::Tensor size_tensor;
  archive.read(key + "/size", size_tensor);
  const size_t size = size_tensor.item<int64_t>();
  for (size_t index = 0; index < size; ++index) {
    buffers.emplace_back();
    archive.read(
        key + "/" + c10::to_string(index), buffers.back(), /*is_buffer=*/true);
  }
}

#define _TORCH_OPTIM_SERIALIZE(name) \
  torch::optim::serialize(archive, #name, self.name)

#define _TORCH_OPTIM_SERIALIZE_WITH_TEMPLATE_ARG(OptimizerName) \
  torch::optim::serialize<OptimizerName##ParamState, OptimizerName##Options>(archive, self)

#define _TORCH_OPTIM_SERIALIZE_TORCH_ARG(name) \
  archive.write(#name, IValue(name()))

#define _TORCH_OPTIM_DESERIALIZE_TORCH_ARG(T, name) \
{ \
  c10::IValue ivalue; \
  archive.read(#name, ivalue); \
  name(ivalue.to<T>()); \
}
} // namespace optim
} // namespace torch
