// Copyright (c) 2022 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.

#include "paddle/phi/kernels/uniform_kernel.h"

#include <thrust/random.h>

#include "gflags/gflags.h"
#include "paddle/phi/core/kernel_registry.h"
#include "paddle/phi/kernels/funcs/distribution_helper.h"
#include "paddle/phi/kernels/funcs/index_impl.cu.h"

namespace phi {

template <typename T>
struct UniformGenerator {
  T min_, max_;
  unsigned int seed_;
  T diag_val_;
  unsigned int diag_num_;
  unsigned int diag_step_;
  __host__ __device__ UniformGenerator(
      T min, T max, int seed, int diag_num, int diag_step, T diag_val)
      : min_(min),
        max_(max),
        seed_(seed),
        diag_num_(diag_num),
        diag_step_(diag_step),
        diag_val_(diag_val) {}

  __host__ __device__ T operator()(const unsigned int n) const {
    thrust::minstd_rand rng;
    rng.seed(seed_);
    thrust::uniform_real_distribution<T> dist(min_, max_);
    rng.discard(n);
    T out = dist(rng);
    unsigned int remainder = n % (diag_step_ + 1);
    if (remainder == 0 && diag_num_ > n / (diag_step_ + 1)) {
      out = diag_val_;
    }
    return out;
  }
};

template <typename T, typename Context>
void UniformKernel(const Context& dev_ctx,
                   const IntArray& shape,
                   DataType dtype,
                   const Scalar& min,
                   const Scalar& max,
                   int seed,
                   DenseTensor* out) {
  out->Resize(phi::make_ddim(shape.GetData()));
  dev_ctx.template Alloc<T>(out);
  if (seed == 0) {
    // Use global Generator seed
    using MT = typename phi::dtype::MPTypeTrait<T>::Type;
    funcs::uniform_distribution<MT> dist;
    funcs::uniform_real_transform<MT> trans(min.to<float>(), max.to<float>());
    funcs::distribution_and_transform<T>(dev_ctx, out, dist, trans);
  } else {
    // Use OP seed
    auto func = UniformGenerator<T>(static_cast<T>(min.to<float>()),
                                    static_cast<T>(max.to<float>()),
                                    seed,
                                    0,
                                    0,
                                    static_cast<T>(0.0));
    IndexKernel<T, UniformGenerator<T>>(dev_ctx, out, func);
  }
}

}  // namespace phi

PD_REGISTER_KERNEL(uniform,
                   GPU,
                   ALL_LAYOUT,
                   phi::UniformKernel,
                   float,
                   double,
                   phi::dtype::float16,
                   phi::dtype::bfloat16) {}