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

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 "paddle/framework/op_registry.h"
#include "paddle/operators/net_op.h"

namespace paddle {
namespace operators {

class InterpOp : public NetOp {
 public:
  InterpOp(const std::string &type, const framework::VariableNameMap &inputs,
           const framework::VariableNameMap &outputs,
           const framework::AttributeMap &attrs)
      : NetOp(type, inputs, outputs, attrs) {
    PADDLE_ENFORCE_NE(Input("X"), framework::kEmptyVarName,
                      "Input(X) of InterpOp should not be null.");
    PADDLE_ENFORCE_NE(Input("Y"), framework::kEmptyVarName,
                      "Input(Y) of InterpOp should not be null.");
    PADDLE_ENFORCE_NE(Input("W"), framework::kEmptyVarName,
                      "Input(W) of InterpOp should not be null.");
    PADDLE_ENFORCE_NE(Output("SubOut"), framework::kEmptyVarName,
                      "Output(SubOut) of InterpOp should not be null.");
    PADDLE_ENFORCE_NE(Output("MulOut"), framework::kEmptyVarName,
                      "Output(MulOut) of InterpOp should not be null.");
    PADDLE_ENFORCE_NE(Output("Out"), framework::kEmptyVarName,
                      "Output(Out) of InterpOp should not be null.");

    // SubOut = X - Y
    auto x = Input("X");
    auto y = Input("Y");
    auto sub_out = Output("SubOut");
    AppendOp(framework::OpRegistry::CreateOp(
        "elementwise_sub", {{"X", {x}}, {"Y", {y}}}, {{"Out", {sub_out}}}, {}));

    // MulOut = SubOut * W = (X - Y) * W
    auto w = Input("W");
    auto mul_out = Output("MulOut");
    AppendOp(framework::OpRegistry::CreateOp(
        "elementwise_mul", {{"X", {sub_out}}, {"Y", {w}}}, {{"Out", {mul_out}}},
        {{"axis", 0}}));

    // Out = MulOut + Y = (X - Y) * W + Y = X * W + Y * (1 - W)
    AppendOp(framework::OpRegistry::CreateOp("elementwise_add",
                                             {{"X", {mul_out}}, {"Y", {y}}},
                                             {{"Out", {Output("Out")}}}, {}));

    CompleteAddOp(false);
  }
};

class InterpOpMaker : public framework::OpProtoAndCheckerMaker {
 public:
  InterpOpMaker(framework::OpProto *proto, framework::OpAttrChecker *op_checker)
      : OpProtoAndCheckerMaker(proto, op_checker) {
    AddInput("X",
             "(Tensor), 2-D Matrix of shape [batch_size, data_dim]"
             "containing data samples, the first input of interp_op");
    AddInput("Y",
             "(Tensor), 2-D Matrix of shape `[batch_size, data_dim]`"
             "containing data samples, the second input of interp_op");
    AddInput("W",
             "(Tensor), 1-D Vector of shape [batch_size],"
             "the interpolated values in the half-open interval [0.0, 1.0)");
    AddOutput("SubOut",
              "(Tensor), the intermediate subtraction outputs, saving X - Y.")
        .AsIntermediate();
    AddOutput("MulOut",
              "(Tensor), the intermediate multiplication outputs,"
              "saving the elementwise multiplication of (X - Y) and W.")
        .AsIntermediate();
    AddOutput("Out",
              "(Tensor), the output of interp_op, same shape with X,"
              "returns the first-dimensional piecewise linear interpolant "
              "between X and Y");
    AddComment(R"DOC(
    Linear Interpolation with two inputs, used in NEURAL TURING MACHINE.

    Equation:
      Out.row[i] = X.row[i] * W[i] + Y.row[i] * (1 - W[i])
                 = (X.row[i] - Y.row[i]) * W[i] + Y.row[i]

    Example:
      X = [[1,2],[3,4]],
      Y = [[2,1],[4,3]],
      W = [0.3, 0.4]

      Then, Out = [[1.7,1.3],[3.6,3.4]]

      where 1.7 = 1*0.3+2*(1-0.3),
            1.3 = 2*0.3+1*(1-0.3),
            3.6 = 3*0.4+4*(1-0.4),
            3.4 = 4*0.4+3*(1-0.4)
)DOC");
  }
};

}  // namespace operators
}  // namespace paddle

namespace ops = paddle::operators;
REGISTER_OP_WITHOUT_GRADIENT(interp, ops::InterpOp, ops::InterpOpMaker);