/* Copyright (c) 2018 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. */

#pragma once

#include <numeric>  // std::iota
#include <sstream>
#include <vector>
#include "glog/logging.h"
#include "paddle/fluid/framework/op_registry.h"
#include "paddle/fluid/operators/detail/safe_ref.h"

namespace paddle {
namespace operators {

template <typename DeviceContext, typename T>
struct SequenceExpandFunctor {
  void operator()(
      const DeviceContext &ctx, const framework::LoDTensor &x,
      const framework::Vector<size_t> &ref_lod, /*expand referenced lod*/
      framework::LoDTensor *out);
};

template <typename DeviceContext, typename T>
struct SequenceExpandAsGradFunctor {
  void operator()(
      const DeviceContext &ctx, const framework::LoDTensor &dout,
      const framework::Vector<size_t> &ref_lod, /*expand referenced lod*/
      framework::LoDTensor *dx);
};

template <typename T>
struct SequenceExpandFunctor<platform::CPUDeviceContext, T> {
  void operator()(
      const platform::CPUDeviceContext &context, const framework::LoDTensor &x,
      const framework::Vector<size_t> &ref_lod, /*expand referenced lod*/
      framework::LoDTensor *out) {
    int64_t hight = x.dims()[0];
    int64_t width = framework::product(x.dims()) / hight;

    const T *in_data = x.data<T>();
    T *out_data = out->mutable_data<T>(context.GetPlace());

    for (int h_id = 0; h_id < hight; ++h_id) {
      size_t span = ref_lod[h_id + 1] - ref_lod[h_id];
      if (span == 0) continue;
      const T *src = in_data + h_id * width;
      for (int64_t w_id = 0; w_id < width; ++w_id) {
        T ele = src[w_id];
        size_t offset = ref_lod[h_id] * width;
        for (size_t k = 0; k < span; ++k) {
          out_data[offset + k * width + w_id] = ele;
        }
      }
    }
  }
};

template <typename DeviceContext, typename T>
class SequenceExpandAsKernel : public framework::OpKernel<T> {
 public:
  void Compute(const framework::ExecutionContext &context) const override {
    auto *x = context.Input<framework::LoDTensor>("X");
    auto *y = context.Input<framework::LoDTensor>("Y");
    auto *out = context.Output<framework::LoDTensor>("Out");

    auto &y_lod = y->lod();
    PADDLE_ENFORCE_EQ(y_lod.size(), 1, "LoD of Y should be 1.");
    PADDLE_ENFORCE_GT(y_lod[0].size(), 1, ".");

    out->mutable_data<T>(context.GetPlace());

    auto &dev_ctx = context.template device_context<DeviceContext>();
    SequenceExpandFunctor<DeviceContext, T> seq_espand_functor;
    seq_espand_functor(dev_ctx, *x, y_lod[0], out);
  }
};

/*
 *Given Grad(Out)
 *
 *    Grad(Out).lod = [[0,              3,            6]]
 *    Grad(Out).data = [0.1, 0.2, 0.3, 0.4, 0.5, 0.6]
 * Then
 *    Grad(X).data = [(0.1 + 0.2 + 0.3), (0.4 + 0.5 + 0.6)]
 *                 = [0.6, 1.5]
 *    Grad(X).lod = Input(X).lod
 *
 * */
template <typename T>
struct SequenceExpandAsGradFunctor<platform::CPUDeviceContext, T> {
  void operator()(
      const platform::CPUDeviceContext &context,
      const framework::LoDTensor &dout,
      const framework::Vector<size_t> &ref_lod, /*expand referenced lod*/
      framework::LoDTensor *dx) {
    int64_t hight = dx->dims()[0];
    int64_t width = framework::product(dx->dims()) / hight;

    const T *dout_data = dout.data<T>();
    T *dx_data = dx->mutable_data<T>(context.GetPlace());

    for (int64_t h_id = 0; h_id < hight; ++h_id) {
      T *dst = dx_data + h_id * width;
      size_t span = ref_lod[h_id + 1] - ref_lod[h_id];
      for (int64_t w_id = 0; w_id < width; ++w_id) {
        T result = 0;
        for (size_t k = 0; k < span; ++k) {
          size_t offset = (ref_lod[h_id] + k) * width;
          result += dout_data[offset + w_id];
        }
        dst[w_id] = result;
      }
    }
  }
};

template <typename DeviceContext, typename T>
class SequenceExpandAsGradKernel : public framework::OpKernel<T> {
 public:
  void Compute(const framework::ExecutionContext &context) const override {
    auto *g_out =
        context.Input<framework::LoDTensor>(framework::GradVarName("Out"));
    auto *y = context.Input<framework::LoDTensor>("Y");
    auto *g_x =
        context.Output<framework::LoDTensor>(framework::GradVarName("X"));

    g_x->mutable_data<T>(context.GetPlace());

    SequenceExpandAsGradFunctor<DeviceContext, T> functor;
    functor(context.template device_context<DeviceContext>(), *g_out,
            y->lod()[0], g_x);
  }
};

}  // namespace operators
}  // namespace paddle
