// ----------------------------------------------------------------------------
// Copyright 2017 Nervana Systems 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
// ----------------------------------------------------------------------------

#pragma once

#include "ngraph/ops/op.hpp"

namespace ngraph
{
    namespace op
    {
        /// \brief Axis-reverse operation.
        ///
        /// Reverses the direction of zero or more axes in a tensor, where "reversing" an axis means that at the output tensor.
        ///
        /// ## Parameters
        ///
        /// |                 | Description              |
        /// | --------------- | ------------------------ |
        /// | `reversed_axes` | The axes to be reversed. |
        ///
        /// ## Inputs
        ///
        /// |       | Type                              | Description                            |
        /// | ----- | --------------------------------- | -------------------------------------- |
        /// | `arg` | \f$E[d_1,\dots,d_n]~(n \geq 0)\f$ | An input tensor of any type and shape. |
        ///
        /// ## Output
        ///
        /// | Type                   | Description                                                                                                                                                               |
        /// | ---------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
        /// | \f$E[d_1,\dots,d_n]\f$ | The tensor \f$T\f$, where \f$T[i_1,\dots,i_n] = \texttt{arg}[j_1,\dots,j_n]\f$ and \f$j_k = d_k - i_k - 1\f$ if axis \f$k\f$ is in the reverse set; else \f$j_k = i_k\f$. |
        class Reverse : public RequiresTensorViewArgs
        {
        public:
            /// \brief Constructs a reverse operation.
            ///
            /// \param arg The input tensor view, some of whose axes are to be reversed.
            /// \param reversed_axes The axes to reverse.
            Reverse(const std::shared_ptr<Node>& arg, const AxisSet& reversed_axes);

            virtual std::shared_ptr<Node> copy_with_new_args(
                const std::vector<std::shared_ptr<Node>>& new_args) const override
            {
                if (new_args.size() != 1)
                    throw ngraph_error("Incorrect number of new arguments");
                return std::make_shared<Reverse>(new_args.at(0), m_reversed_axes);
            }

            /// \return The set of axes to reverse.
            const AxisSet& get_reversed_axes() const { return m_reversed_axes; }
        protected:
            virtual void generate_adjoints(autodiff::Adjoints& adjoints,
                                           const std::shared_ptr<Node>& delta) override;

            const AxisSet m_reversed_axes;
        };
    }
}
