#include <torch/optim/rmsprop.h>

#include <torch/csrc/autograd/variable.h>
#include <torch/serialize/archive.h>
#include <torch/utils.h>

#include <ATen/ATen.h>

#include <functional>

namespace torch {
namespace optim {

RMSpropOptions::RMSpropOptions(double lr) : lr_(lr) {}

bool operator==(const RMSpropOptions& lhs, const RMSpropOptions& rhs) {
  return (lhs.lr() == rhs.lr()) &&
          (lhs.alpha() == rhs.alpha()) &&
          (lhs.eps() == rhs.eps()) &&
          (lhs.weight_decay() == rhs.weight_decay()) &&
          (lhs.momentum() == rhs.momentum()) &&
          (lhs.centered() == rhs.centered());
}

void RMSpropOptions::serialize(torch::serialize::OutputArchive& archive) const {
  _TORCH_OPTIM_SERIALIZE_TORCH_ARG(lr);
  _TORCH_OPTIM_SERIALIZE_TORCH_ARG(alpha);
  _TORCH_OPTIM_SERIALIZE_TORCH_ARG(eps);
  _TORCH_OPTIM_SERIALIZE_TORCH_ARG(weight_decay);
  _TORCH_OPTIM_SERIALIZE_TORCH_ARG(momentum);
  _TORCH_OPTIM_SERIALIZE_TORCH_ARG(centered);
}

void RMSpropOptions::serialize(torch::serialize::InputArchive& archive) {
  _TORCH_OPTIM_DESERIALIZE_TORCH_ARG(double, lr);
  _TORCH_OPTIM_DESERIALIZE_TORCH_ARG(double, alpha);
  _TORCH_OPTIM_DESERIALIZE_TORCH_ARG(double, eps);
  _TORCH_OPTIM_DESERIALIZE_TORCH_ARG(double, weight_decay);
  _TORCH_OPTIM_DESERIALIZE_TORCH_ARG(double, momentum);
  _TORCH_OPTIM_DESERIALIZE_TORCH_ARG(bool, centered);
}

bool operator==(const RMSpropParamState& lhs, const RMSpropParamState& rhs) {
  return (lhs.step() == rhs.step()) &&
         torch::equal(lhs.square_avg(), rhs.square_avg()) &&
         torch::equal_if_defined(lhs.momentum_buffer(), rhs.momentum_buffer()) &&
         torch::equal_if_defined(lhs.grad_avg(), rhs.grad_avg());
}

void RMSpropParamState::serialize(torch::serialize::OutputArchive& archive) const {
  _TORCH_OPTIM_SERIALIZE_TORCH_ARG(step);
  _TORCH_OPTIM_SERIALIZE_TORCH_ARG(square_avg);
  _TORCH_OPTIM_SERIALIZE_TORCH_ARG(momentum_buffer);
  _TORCH_OPTIM_SERIALIZE_TORCH_ARG(grad_avg);
}

void RMSpropParamState::serialize(torch::serialize::InputArchive& archive) {
  _TORCH_OPTIM_DESERIALIZE_TORCH_ARG(int64_t, step);
  _TORCH_OPTIM_DESERIALIZE_TORCH_ARG(Tensor, square_avg);
  _TORCH_OPTIM_DESERIALIZE_TORCH_ARG(Tensor, momentum_buffer);
  _TORCH_OPTIM_DESERIALIZE_TORCH_ARG(Tensor, grad_avg);
}

/// Adapted from
/// https://github.com/pytorch/pytorch/blob/master/torch/optim/rmsprop.py
Tensor RMSprop::step(LossClosure closure)  {
  NoGradGuard no_grad;
  Tensor loss = {};
  if (closure != nullptr) {
    at::AutoGradMode enable_grad(true);
    loss = closure();
  }
  for (auto& group : param_groups_) {
    for (auto& p : group.params()) {
      if (!p.grad().defined()) {
        continue;
      }
      auto grad = p.grad();
      TORCH_CHECK(!grad.is_sparse(), "RMSprop does not support sparse gradients");
      auto param_state = state_.find(c10::guts::to_string(p.unsafeGetTensorImpl()));
      auto& options = static_cast<RMSpropOptions&>(group.options());

      // State initialization
      if (param_state == state_.end()) {
        auto state = std::make_unique<RMSpropParamState>();
        state->step(0);
        state->square_avg(torch::zeros_like(p, MemoryFormat::Preserve));
        if (options.momentum() > 0) {
          state->momentum_buffer(torch::zeros_like(p, MemoryFormat::Preserve));
        }
        if (options.centered()) {
          state->grad_avg(torch::zeros_like(p, MemoryFormat::Preserve));
        }
        state_[c10::guts::to_string(p.unsafeGetTensorImpl())] = std::move(state);
      }

      auto& state = static_cast<RMSpropParamState&>(*state_[c10::guts::to_string(p.unsafeGetTensorImpl())]);
      auto& square_avg = state.square_avg();
      auto alpha = options.alpha();

      state.step(state.step() + 1);

      if (options.weight_decay() != 0) {
        grad = grad.add(p, options.weight_decay());
      }

      square_avg.mul_(alpha).addcmul_(grad, grad, 1 - alpha);

      Tensor avg;
      if (options.centered()) {
        auto& grad_avg = state.grad_avg();
        grad_avg.mul_(alpha).add_(grad, 1-alpha);
        avg = square_avg.addcmul(grad_avg, grad_avg, -1).sqrt_().add_(options.eps());
      } else {
        avg = square_avg.sqrt().add_(options.eps());
      }

      if (options.momentum() > 0) {
        auto& buf = state.momentum_buffer();
        buf.mul_(options.momentum()).addcdiv_(grad, avg);
        // Need to avoid version tracking for parameter.
        p.add_(buf, -options.lr());
      } else {
        // Need to avoid version tracking for parameter.
        p.addcdiv_(grad, avg, -options.lr());
      }
    }
  }
  return loss;
}

void RMSprop::save(serialize::OutputArchive& archive) const {
  serialize(*this, archive);
}

void RMSprop::load(serialize::InputArchive& archive) {
  IValue pytorch_version;
  if (archive.try_read("pytorch_version", pytorch_version)) {
    serialize(*this, archive);
  }
  else { // deserializing archives saved in old format (prior to version 1.5.0)
    TORCH_WARN(
      "Your serialized RMSprop optimizer is still using the old serialization format. "
      "The step value in state will be set to 0 because the old RMSprop optimizer didn't track the step value."
      "You should re-save your RMSprop optimizer to use the new serialization format.");
    std::vector<Tensor> square_average_buffers;
    std::vector<Tensor> momentum_buffers;
    std::vector<Tensor> grad_average_buffers;
    torch::optim::serialize(archive, "square_average_buffers", square_average_buffers);
    torch::optim::serialize(archive, "momentum_buffers", momentum_buffers);
    torch::optim::serialize(archive, "grad_average_buffers", grad_average_buffers);
    // since there were no param_groups prior to version 1.5.0, assuming all tensors are now in one param_group
    std::vector<Tensor> params = param_groups_.at(0).params();
    for (size_t idx = 0; idx < square_average_buffers.size(); idx++) {
      auto state = std::make_unique<RMSpropParamState>();
      state->square_avg(square_average_buffers[idx]);
      if(idx < momentum_buffers.size()) {
        state->momentum_buffer(momentum_buffers.at(idx));
      }
      if(idx < grad_average_buffers.size()) {
        state->grad_avg(grad_average_buffers.at(idx));
      }
      state_[c10::guts::to_string(params[idx].unsafeGetTensorImpl())] = std::move(state);
    }
  }
}
} // namespace optim
} // namespace torch
