// 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 "paddle/phi/common/complex.h"
#include "paddle/phi/common/type_traits.h"
#include "paddle/phi/kernels/complex_kernel.h"

#include "paddle/common/flags.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, bool IsComplex>
struct UniformKernelImpl {};

template <typename T, typename Context>
struct UniformKernelImpl<T, Context, true> {
  static void Apply(const Context& dev_ctx,
                    const Scalar& min,
                    const Scalar& max,
                    int seed,
                    DenseTensor* out) {
    using RealType = dtype::Real<T>;
    RealType min_val = min.to<RealType>();
    RealType max_val = max.to<RealType>();

    if (seed == 0) {
      funcs::uniform_distribution<RealType> dist;
      funcs::uniform_real_transform<RealType> trans(min_val, max_val);
      funcs::distribution_and_transform<T>(dev_ctx, out, dist, trans);
    } else {
      auto func = [=] __device__(int64_t idx) {
        thrust::minstd_rand engine;
        engine.seed(seed);
        engine.discard(idx);
        thrust::uniform_real_distribution<RealType> dist(min_val, max_val);
        return dist(engine);
      };  // NOLINT(readability/braces)
      IndexKernel<T, decltype(func)>(dev_ctx, out, func);
    }
  }
};

template <typename Context>
struct UniformKernelImpl<dtype::complex<float>, Context, true> {
  static void Apply(const Context& dev_ctx,
                    const Scalar& min,
                    const Scalar& max,
                    int seed,
                    DenseTensor* out) {
    using T = dtype::complex<float>;
    using RealType = float;
    RealType min_val = min.to<RealType>();
    RealType max_val = max.to<RealType>();

    auto gen_cuda = dev_ctx.GetGenerator();

    size_t size = out->numel();
    size_t increment = size * 2;

    auto seed_offset = gen_cuda->IncrementOffset(increment);
    uint64_t actual_seed = seed_offset.first;
    uint64_t offset = seed_offset.second;

    auto func = [=] __device__(int64_t idx) {
      thrust::minstd_rand engine;
      engine.seed(actual_seed);
      engine.discard(offset + idx * 2);
      thrust::uniform_real_distribution<RealType> dist(min_val, max_val);
      RealType real_val = dist(engine);
      RealType imag_val = dist(engine);
      return T(real_val, imag_val);
    };  // NOLINT(readability/braces)
    IndexKernel<T, decltype(func)>(dev_ctx, out, func);
  }
};

template <typename Context>
struct UniformKernelImpl<dtype::complex<double>, Context, true> {
  static void Apply(const Context& dev_ctx,
                    const Scalar& min,
                    const Scalar& max,
                    int seed,
                    DenseTensor* out) {
    using T = dtype::complex<double>;
    using RealType = double;
    RealType min_val = min.to<RealType>();
    RealType max_val = max.to<RealType>();

    auto gen_cuda = dev_ctx.GetGenerator();

    size_t size = out->numel();
    size_t increment = size * 2;

    auto seed_offset = gen_cuda->IncrementOffset(increment);
    uint64_t actual_seed = seed_offset.first;
    uint64_t offset = seed_offset.second;

    auto func = [=] __device__(int64_t idx) {
      thrust::minstd_rand engine;
      engine.seed(actual_seed);
      engine.discard(offset + idx * 2);
      thrust::uniform_real_distribution<RealType> dist(min_val, max_val);
      RealType real_val = dist(engine);
      RealType imag_val = dist(engine);
      return T(real_val, imag_val);
    };  // NOLINT(readability/braces)
    IndexKernel<T, decltype(func)>(dev_ctx, out, func);
  }
};

template <typename T, typename Context>
struct UniformKernelImpl<T, Context, false> {
  static void Apply(const Context& dev_ctx,
                    const Scalar& min,
                    const Scalar& max,
                    int seed,
                    DenseTensor* out) {
    if (seed == 0) {
      using MT = typename MPTypeTrait<T>::Type;
      funcs::uniform_distribution<MT> dist;
      funcs::uniform_real_transform<MT, T> trans(static_cast<MT>(min.to<T>()),
                                                 static_cast<MT>(max.to<T>()));
      funcs::distribution_and_transform<T>(dev_ctx, out, dist, trans);
    } else {
      auto func = UniformGenerator<T>(
          static_cast<T>(min.to<float>()),
          static_cast<T>(max.to<float>()),
          seed,
          0,
          0,
          static_cast<T>(0.0));  // NOLINT(readability/braces)
      IndexKernel<T, UniformGenerator<T>>(dev_ctx, out, func);
    }
  }
};

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(shape.GetData());
  dev_ctx.template Alloc<T>(out);

  constexpr bool is_complex = std::is_same<T, dtype::complex<float>>::value ||
                              std::is_same<T, dtype::complex<double>>::value;

  UniformKernelImpl<T, Context, is_complex>::Apply(
      dev_ctx, min, max, seed, out);
}

}  // namespace phi

PD_REGISTER_KERNEL(uniform,
                   GPU,
                   ALL_LAYOUT,
                   phi::UniformKernel,
                   float,
                   double,
                   phi::float16,
                   phi::bfloat16,
                   phi::float8_e4m3fn,
                   phi::complex64,
                   phi::complex128) {}