/* Copyright (c) 2020 PaddlePaddle 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. */

#pragma once

#include <algorithm>

#include "paddle/fluid/framework/op_registry.h"
#include "paddle/fluid/framework/operator.h"
#include "paddle/fluid/operators/math/math_function.h"

namespace paddle {
namespace operators {

using Tensor = framework::Tensor;

template <typename DeviceContext, typename T>
class HistogramKernel : public framework::OpKernel<T> {
 public:
  void Compute(const framework::ExecutionContext& context) const override {
    const Tensor* input = context.Input<framework::Tensor>("X");
    Tensor* output = context.Output<framework::Tensor>("Out");
    auto& nbins = context.Attr<int64_t>("bins");
    auto& minval = context.Attr<int>("min");
    auto& maxval = context.Attr<int>("max");

    const T* input_data = input->data<T>();
    auto input_numel = input->numel();

    int64_t* out_data = output->mutable_data<int64_t>(context.GetPlace());
    math::SetConstant<DeviceContext, int64_t>()(
        context.template device_context<DeviceContext>(), output,
        static_cast<int64_t>(0));

    if (input_data == nullptr) return;

    T output_min = static_cast<T>(minval);
    T output_max = static_cast<T>(maxval);
    if (output_min == output_max) {
      output_min = *std::min_element(input_data, input_data + input_numel);
      output_max = *std::max_element(input_data, input_data + input_numel);
    }
    if (output_min == output_max) {
      output_min = output_min - 1;
      output_max = output_max + 1;
    }

    PADDLE_ENFORCE_EQ(
        (std::isinf(static_cast<float>(output_min)) ||
         std::isnan(static_cast<float>(output_max)) ||
         std::isinf(static_cast<float>(output_min)) ||
         std::isnan(static_cast<float>(output_max))),
        false, platform::errors::OutOfRange("range of min, max is not finite"));
    PADDLE_ENFORCE_GE(
        output_max, output_min,
        platform::errors::InvalidArgument(
            "max must be larger or equal to min. If min and max are both zero, "
            "the minimum and maximum values of the data are used. "
            "But received max is %d, min is %d",
            maxval, minval));

    for (int64_t i = 0; i < input_numel; i++) {
      if (input_data[i] >= output_min && input_data[i] <= output_max) {
        const int64_t bin = (int64_t)((input_data[i] - output_min) * nbins /
                                      (output_max - output_min));
        out_data[std::min(bin, nbins - 1)] += 1;
      }
    }
  }
};

}  // namespace operators
}  // namespace paddle
