/*
Copyright 2020 The OneFlow 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 "oneflow/core/framework/op_expr_grad_function.h"
#include "oneflow/core/framework/op_builder.h"
#include "oneflow/core/framework/op_expr.h"
#include "oneflow/core/framework/op_expr_helper.h"
#include "oneflow/core/framework/op_interpreter/op_interpreter_util.h"

namespace oneflow {
namespace one {

struct DimGatherCaptureState : public AutoGradCaptureState {
  int32_t dim;
  bool requires_grad;
};

class DimGather : public OpExprGradFunction<DimGatherCaptureState> {
 public:
  Maybe<void> Init(const OpExpr& op) override;
  Maybe<void> Capture(DimGatherCaptureState* ctx, const TensorTuple& inputs,
                      const TensorTuple& outputs, const AttrMap& attrs) const override;
  Maybe<void> Apply(const DimGatherCaptureState* ctx, const TensorTuple& out_grads,
                    TensorTuple* in_grads) const override;

 private:
  AttrMap base_attrs_;
  std::shared_ptr<OpExpr> bw_dim_gather_op_;
};

Maybe<void> DimGather::Init(const OpExpr& op) {
  const UserOpExpr* fw_op_expr = dynamic_cast<const UserOpExpr*>(&op);
  CHECK_NOTNULL_OR_RETURN(fw_op_expr);
  base_attrs_ = MakeAttrMapFromUserOpConf(fw_op_expr->proto());
  const std::string& op_name = fw_op_expr->op_name();
  bw_dim_gather_op_ = JUST(op_expr_helper::DimScatterAddLikeOp(0, GradientOpName(op_name)));
  return Maybe<void>::Ok();
}

Maybe<void> DimGather::Capture(DimGatherCaptureState* ctx, const TensorTuple& inputs,
                               const TensorTuple& outputs, const AttrMap& attrs) const {
  ctx->requires_grad = inputs.at(0)->requires_grad();
  if (!ctx->requires_grad) { return Maybe<void>::Ok(); }

  ctx->SaveTensorForBackward(inputs.at(1));
  ctx->SaveTensorForBackward(inputs.at(0));

  ComposedAttrMap composed_attrs(attrs, base_attrs_);
  ctx->dim = JUST(composed_attrs.GetAttr<int32_t>("dim"));
  return Maybe<void>::Ok();
}

Maybe<void> DimGather::Apply(const DimGatherCaptureState* ctx, const TensorTuple& out_grads,
                             TensorTuple* in_grads) const {
  if (!ctx->requires_grad) { return Maybe<void>::Ok(); }
  CHECK_EQ_OR_RETURN(out_grads.size(), 1);
  const std::shared_ptr<oneflow::one::Tensor>& index = ctx->SavedTensors().at(0);
  const std::shared_ptr<oneflow::one::Tensor>& like = ctx->SavedTensors().at(1);

  MutableAttrMap attrs;
  JUST(attrs.SetAttr<int32_t>("dim", ctx->dim));
  in_grads->at(0) = JUST(
      OpInterpUtil::Dispatch<Tensor>(*bw_dim_gather_op_, {like, index, out_grads.at(0)}, attrs));
  return Maybe<void>::Ok();
}

REGISTER_OP_EXPR_GRAD_FUNCTION("dim_gather", DimGather);

}  // namespace one
}  // namespace oneflow
