///////////////////////////////////////////////////////////////////////

// File:        reversed.h

// Description: Runs a single network on time-reversed input, reversing output.

// Author:      Ray Smith

//

// (C) Copyright 2013, Google Inc.

// 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.

///////////////////////////////////////////////////////////////////////

#ifndef TESSERACT_LSTM_REVERSED_H_

#define TESSERACT_LSTM_REVERSED_H_

#include "matrix.h"

#include "plumbing.h"

namespace tesseract {

// C++ Implementation of the Reversed class from lstm.py.

class Reversed : public Plumbing {

public:

  TESS_API

  explicit Reversed(const std::string &name, NetworkType type);

  ~Reversed() override = default;

  // Returns the shape output from the network given an input shape (which may

  // be partially unknown ie zero).

  StaticShape OutputShape(const StaticShape &input_shape) const override;

  std::string spec() const override {

    std::string spec(type_ == NT_XREVERSED ? "Rx" : (type_ == NT_YREVERSED ? "Ry" : "Txy"));

    // For most simple cases, we will output Rx<net> or Ry<net> where <net> is

    // the network in stack_[0], but in the special case that <net> is an

    // LSTM, we will just output the LSTM's spec modified to take the reversal

    // into account. This is because when the user specified Lfy64, we actually

    // generated TxyLfx64, and if the user specified Lrx64 we actually

    // generated RxLfx64, and we want to display what the user asked for.

    std::string net_spec(stack_[0]->spec());

    if (net_spec[0] == 'L') {

      // Setup a from and to character according to the type of the reversal

      // such that the LSTM spec gets modified to the spec that the user

      // asked for

      char from = 'f';

      char to = 'r';

      if (type_ == NT_XYTRANSPOSE) {

        from = 'x';

        to = 'y';

      }

      // Change the from char to the to char.

      for (auto &it : net_spec) {

        if (it == from) {

          it = to;

        }

      }

      spec += net_spec;

      return spec;

    }

    spec += net_spec;

    return spec;

  }

  // Takes ownership of the given network to make it the reversed one.

  TESS_API

  void SetNetwork(Network *network);

  // Runs forward propagation of activations on the input line.

  // See Network for a detailed discussion of the arguments.

  void Forward(bool debug, const NetworkIO &input, const TransposedArray *input_transpose,

               NetworkScratch *scratch, NetworkIO *output) override;

  // Runs backward propagation of errors on the deltas line.

  // See Network for a detailed discussion of the arguments.

  bool Backward(bool debug, const NetworkIO &fwd_deltas, NetworkScratch *scratch,

                NetworkIO *back_deltas) override;

private:

  // Copies src to *dest with the reversal according to type_.

  void ReverseData(const NetworkIO &src, NetworkIO *dest) const;

};

} // namespace tesseract.

#endif // TESSERACT_LSTM_REVERSED_H_