/*******************************************************************************
 * Copyright (c) 2015-2018 Skymind, Inc.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Apache License, Version 2.0 which is available at
 * https://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.
 *
 * SPDX-License-Identifier: Apache-2.0
 ******************************************************************************/

//
//  @author sgazeos@gmail.com
//

#include <ops/declarable/helpers/nth_element.h>
#include <helpers/TAD.h>
#include <helpers/ShapeUtils.h>
#include <helpers/PointersManager.h>
#include <legacy/NativeOps.h>
#include <helpers/ConstantTadHelper.h>

namespace sd {
namespace ops {
namespace helpers {

    template <typename T>
    static __global__ void fillUpElementKernel(void* outputBuffer, Nd4jLong const* outputShapeInfo, void* inputBuffer, Nd4jLong const* inputShapeInfo, Nd4jLong const* pTadShape, Nd4jLong const* pTadOffsets, Nd4jLong n) {
        __shared__ Nd4jLong bufferLength;

        auto z = reinterpret_cast<T*>(outputBuffer);
        auto x = reinterpret_cast<T*>(inputBuffer);

        if (threadIdx.x == 0)
            bufferLength = shape::length(outputShapeInfo);

        __syncthreads();

        const auto tid = blockIdx.x * blockDim.x + threadIdx.x;
        const auto step = gridDim.x * blockDim.x;
        for (int t = tid; t < bufferLength; t += step) {
            auto tX = x + pTadOffsets[t];
            z[shape::getIndexOffset(t, outputShapeInfo)] = tX[shape::getIndexOffset(n, pTadShape)]; //tX];
        }
    }

    template <typename T>
    void nthElementFunctor_(sd::LaunchContext * context, NDArray* input, Nd4jLong n, NDArray* output, bool reverse) {

        NDArray::prepareSpecialUse({output}, {input});
        NDArray sortedVals(*input);
        Nd4jPointer params[2];
        params[0] = context;
        params[1] = context->getCudaStream();
        // Nth element in sorted sequence : basic algorithm sort and retrieve nth element in sorted
        if (input->isVector()) {
            sort(params, nullptr, sortedVals.shapeInfo(), sortedVals.specialBuffer(), sortedVals.specialShapeInfo(), reverse);

            cudaMemcpy(reinterpret_cast<T*>(output->specialBuffer()), reinterpret_cast<T*>(sortedVals.specialBuffer()) + n, sizeof(T), cudaMemcpyDeviceToDevice);
        }
        else { // rank greater than 1
            std::vector<int> lastDims({input->rankOf() - 1});// = ShapeUtils::evalDimsToExclude(input->rankOf(), {input->rankOf() - 1});

            auto packX = sd::ConstantTadHelper::getInstance().tadForDimensions(sortedVals.shapeInfo(), lastDims);

            auto pTadShape = packX.specialShapeInfo();
            auto pTadShapeH = packX.primaryShapeInfo();
            auto pTadOffsets = packX.specialOffsets();
            sortTad(params, sortedVals.buffer(), sortedVals.shapeInfo(), sortedVals.specialBuffer(), sortedVals.specialShapeInfo(), lastDims.data(), lastDims.size(), pTadShape, pTadOffsets, reverse);
            sortedVals.tickWriteDevice();
            sortedVals.syncToHost();
            auto stream = context->getCudaStream();
            fillUpElementKernel<T><<<32, 64, 1024, *stream>>>(output->specialBuffer(), output->specialShapeInfo(), sortedVals.specialBuffer(), sortedVals.specialShapeInfo(), pTadShape, pTadOffsets, n);
        }
        NDArray::registerSpecialUse({output}, {input});
    }
    void nthElementFunctor(sd::LaunchContext * context, NDArray* input, Nd4jLong n, NDArray* output, bool reverse) {
    BUILD_SINGLE_SELECTOR(input->dataType(), nthElementFunctor_, (context, input, n, output, reverse), LIBND4J_TYPES);

    }

}
}
}