/*************************************************************************
 * Copyright (c) 2022-2026, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 *
 * See LICENSE for license information.
 ************************************************************************/

#include <assert.h>
#include <cuda.h>
#include <cuda_fp16.h>
#include <cuda_profiler_api.h>
#include <cuda_runtime.h>
#include <stdint.h>
#include <transformer_engine/softmax.h>

#include <array>
#include <cfloat>
#include <functional>
#include <limits>

#include "../common.h"
#include "../util/logging.h"
#include "../utils.cuh"

namespace transformer_engine {

template <typename Datatype, int ELEMENTS_PER_LDG>
__device__ __inline__ void copy_vector(Datatype *dst, const Datatype *src);

template <>
__device__ __inline__ void copy_vector<bf16, 1>(bf16 *dst, const bf16 *src) {
  *dst = *src;
}

template <>
__device__ __inline__ void copy_vector<bf16, 4>(bf16 *dst, const bf16 *src) {
  *((uint64_t *)dst) = *((uint64_t *)src);  // NOLINT(*)
}

template <>
__device__ __inline__ void copy_vector<fp16, 1>(fp16 *dst, const fp16 *src) {
  *dst = *src;
}

template <>
__device__ __inline__ void copy_vector<fp16, 4>(fp16 *dst, const fp16 *src) {
  *((uint64_t *)dst) = *((uint64_t *)src);  // NOLINT(*)
}

template <>
__device__ __inline__ void copy_vector<uint8_t, 1>(uint8_t *dst, const uint8_t *src) {
  *dst = *src;
}

template <>
__device__ __inline__ void copy_vector<uint8_t, 4>(uint8_t *dst, const uint8_t *src) {
  *((uint32_t *)dst) = *((uint32_t *)src);  // NOLINT(*)
}

template <typename Datatype, int ELEMENTS_PER_LDG>
__device__ __inline__ void copy_zero_vector(Datatype *dst);

template <>
__device__ __inline__ void copy_zero_vector<bf16, 1>(bf16 *dst) {
  *dst = 0.0f;
}

template <>
__device__ __inline__ void copy_zero_vector<bf16, 4>(bf16 *dst) {
  *((float2 *)dst) = make_float2(0.0f, 0.0f);  // NOLINT(*)
}

template <>
__device__ __inline__ void copy_zero_vector<fp16, 1>(fp16 *dst) {
  *dst = 0.0f;
}

template <>
__device__ __inline__ void copy_zero_vector<fp16, 4>(fp16 *dst) {
  *((float2 *)dst) = make_float2(0.0f, 0.0f);  // NOLINT(*)
}

template <typename T>
struct Add {
  __device__ __forceinline__ T operator()(T a, T b) const { return a + b; }
};

template <typename T>
struct Max {
  __device__ __forceinline__ T operator()(T a, T b) const { return a < b ? b : a; }
};

template <typename T>
__device__ __forceinline__ T WARP_SHFL_XOR_NATIVE(T value, int laneMask, int width = warpSize,
                                                  unsigned int mask = 0xffffffff) {
#if CUDA_VERSION >= 9000
  return __shfl_xor_sync(mask, value, laneMask, width);
#else
  return __shfl_xor(value, laneMask, width);
#endif
}

template <typename acc_t, int WARP_ROWS, int WARP_SIZE, template <typename> class ReduceOp>
__device__ __forceinline__ void warp_reduce(acc_t *sum) {
  ReduceOp<acc_t> r;
#pragma unroll
  for (int offset = WARP_SIZE / 2; offset > 0; offset /= 2) {
#pragma unroll
    for (int i = 0; i < WARP_ROWS; ++i) {
      acc_t b = WARP_SHFL_XOR_NATIVE(sum[i], offset, WARP_SIZE);
      sum[i] = r(sum[i], b);
    }
  }
}

/*
 * Extended softmax (from native aten pytorch) with the following additional features
 * 1) input scaling
 * 2) implicit causal masking
 *
 * works for all cases:
 *  k > q
 *  k < q
 *  k = q
 *
 * where:
 * microbatches = batches * attn_heads * query_seq_len
 * rows = query_seq_len
 * cols = key_seq_len
 */
template <typename input_t, typename output_t, typename acc_t, int log2_elements>
__global__ void scaled_aligned_causal_masked_softmax_warp_forward(output_t *dst, const input_t *src,
                                                                  const acc_t scale,
                                                                  const int microbatches,
                                                                  const int rows, const int cols) {
  // 1) WARP_WIDTH must match the value of warp_size
  // 2) WARP_ROWS must match the value of rows_per_warp
  // of the dispatch_scaled_aligned_causal_masked_softmax_forward method.
  constexpr int next_power_of_two = 1 << log2_elements;
  constexpr int WARP_WIDTH =
      (next_power_of_two < THREADS_PER_WARP) ? next_power_of_two : THREADS_PER_WARP;
  constexpr int WARP_ITERATIONS = next_power_of_two / WARP_WIDTH;
  constexpr int WARP_ROWS = (next_power_of_two <= 128) ? 2 : 1;
  constexpr int ELEMENTS_PER_LDG_STG = (WARP_ITERATIONS < 4) ? 1 : 4;

  const int global_row_idx = (blockIdx.x * blockDim.y + threadIdx.y) * WARP_ROWS;
  const int col = threadIdx.x * ELEMENTS_PER_LDG_STG;

  const size_t thread_offset = global_row_idx * cols + col;

  src += thread_offset;
  dst += thread_offset;

  // load data from global memory into registers WITH scaling
  acc_t elements[WARP_ROWS][WARP_ITERATIONS];
  input_t temp_data[ELEMENTS_PER_LDG_STG];

#pragma unroll
  for (int w = 0; w < WARP_ROWS; ++w) {
    const int microbatch = global_row_idx + w;
    const int i = microbatch % rows;  // local row index of attention matrix
    const int masked_elements = i + cols - rows + 1;

    if (microbatch >= microbatches) {
      break;
    }

#pragma unroll
    for (int it = 0; it < WARP_ITERATIONS; it += ELEMENTS_PER_LDG_STG) {
      const int j = col + it * WARP_WIDTH;
      const int itr_idx = w * cols + it * WARP_WIDTH;

      if (j < masked_elements) {
        copy_vector<input_t, ELEMENTS_PER_LDG_STG>(temp_data, src + itr_idx);
#pragma unroll
        for (int element = 0; element < ELEMENTS_PER_LDG_STG; ++element) {
          if (j + element < masked_elements) {
            elements[w][it + element] = (acc_t)temp_data[element] * scale;
          } else {
            elements[w][it + element] = (acc_t)(-10'000);
          }
        }
      } else {
#pragma unroll
        for (int element = 0; element < ELEMENTS_PER_LDG_STG; ++element) {
          elements[w][it + element] = (acc_t)(-10'000);
        }
      }
    }
  }

  // compute max_value
  acc_t max_value[WARP_ROWS];
#pragma unroll
  for (int w = 0; w < WARP_ROWS; ++w) {
    max_value[w] = elements[w][0];
#pragma unroll
    for (int it = 1; it < WARP_ITERATIONS; ++it) {
      max_value[w] = (max_value[w] > elements[w][it]) ? max_value[w] : elements[w][it];
    }
  }
  warp_reduce<acc_t, WARP_ROWS, WARP_WIDTH, Max>(max_value);

  acc_t sum[WARP_ROWS]{0.0f};
#pragma unroll
  for (int w = 0; w < WARP_ROWS; ++w) {
#pragma unroll
    for (int it = 0; it < WARP_ITERATIONS; ++it) {
      elements[w][it] = expf((elements[w][it] - max_value[w]));
      sum[w] += elements[w][it];
    }
  }
  warp_reduce<acc_t, WARP_ROWS, WARP_WIDTH, Add>(sum);

  output_t out[ELEMENTS_PER_LDG_STG]{0.0f};
// store result
#pragma unroll
  for (int w = 0; w < WARP_ROWS; ++w) {
    const int microbatch = global_row_idx + w;
    const int i = microbatch % rows;
    const int masked_elements = i + cols - rows + 1;

    // out of Attention matrix bounds (rows)
    if (microbatch >= microbatches) {
      break;
    }

#pragma unroll
    for (int it = 0; it < WARP_ITERATIONS; it += ELEMENTS_PER_LDG_STG) {
      const int j = col + it * WARP_WIDTH;  // index of the first column
      const int itr_idx = w * cols + it * WARP_WIDTH;

      if (j < masked_elements) {
#pragma unroll
        for (int element = 0; element < ELEMENTS_PER_LDG_STG; ++element) {
          if (j + element < masked_elements) {
            out[element] = elements[w][it + element] / sum[w];
          } else {
            out[element] = (output_t)(0.0f);
          }
        }
        copy_vector<output_t, ELEMENTS_PER_LDG_STG>(dst + itr_idx, out);
      } else if (j < cols) {
        copy_zero_vector<output_t, ELEMENTS_PER_LDG_STG>(dst + itr_idx);
      } else {
        break;
      }
    }
  }
}

template <typename input_t, typename output_t, typename acc_t, int log2_elements>
__global__ void scaled_aligned_causal_masked_softmax_warp_backward(
    output_t *gradInput, const input_t *grad, const input_t *softmax_output, const acc_t scale,
    const int microbatches, const int rows, const int cols) {
  // 1) WARP_WIDTH must match the value of warp_size
  // 2) WARP_ROWS must match the value of rows_per_warp
  // of the dispatch_scaled_aligned_causal_masked_softmax_forward method.
  constexpr int next_power_of_two = 1 << log2_elements;
  constexpr int WARP_WIDTH =
      (next_power_of_two < THREADS_PER_WARP) ? next_power_of_two : THREADS_PER_WARP;
  constexpr int WARP_ITERATIONS = next_power_of_two / WARP_WIDTH;
  constexpr int WARP_ROWS = (next_power_of_two <= 128) ? 2 : 1;
  constexpr int ELEMENTS_PER_LDG_STG = (WARP_ITERATIONS < 4) ? 1 : 4;

  const int global_row_idx = (blockIdx.x * blockDim.y + threadIdx.y) * WARP_ROWS;
  const int col = threadIdx.x * ELEMENTS_PER_LDG_STG;

  const size_t thread_offset = global_row_idx * cols + col;

  grad += thread_offset;
  softmax_output += thread_offset;
  gradInput += thread_offset;

  // load data from global memory into registers
  acc_t grad_reg[WARP_ROWS][WARP_ITERATIONS]{0.0f};
  acc_t softmax_output_reg[WARP_ROWS][WARP_ITERATIONS]{0.0f};
  input_t temp_grad[ELEMENTS_PER_LDG_STG];
  input_t temp_output[ELEMENTS_PER_LDG_STG];

#pragma unroll
  for (int w = 0; w < WARP_ROWS; ++w) {
    const int microbatch = global_row_idx + w;
    const int i = microbatch % rows;  // local row index of attention matrix
    const int masked_elements = i + cols - rows + 1;

    if (microbatch >= microbatches) {
      break;
    }

#pragma unroll
    for (int it = 0; it < WARP_ITERATIONS; it += ELEMENTS_PER_LDG_STG) {
      const int j = col + it * WARP_WIDTH;  // index of the first column
      const int itr_idx = w * cols + it * WARP_WIDTH;

      if (j < masked_elements) {
        copy_vector<input_t, ELEMENTS_PER_LDG_STG>(temp_grad, grad + itr_idx);
        copy_vector<input_t, ELEMENTS_PER_LDG_STG>(temp_output, softmax_output + itr_idx);
#pragma unroll
        for (int element = 0; element < ELEMENTS_PER_LDG_STG; ++element) {
          if (j + element < masked_elements) {
            softmax_output_reg[w][it + element] = (acc_t)temp_output[element];
            grad_reg[w][it + element] =
                (acc_t)temp_grad[element] * softmax_output_reg[w][it + element];
          }
        }
      }
    }
  }

  acc_t sum[WARP_ROWS];
#pragma unroll
  for (int w = 0; w < WARP_ROWS; ++w) {
    sum[w] = grad_reg[w][0];
#pragma unroll
    for (int it = 1; it < WARP_ITERATIONS; ++it) {
      sum[w] += grad_reg[w][it];
    }
  }

  warp_reduce<acc_t, WARP_ROWS, WARP_WIDTH, Add>(sum);

// store result
#pragma unroll
  for (int w = 0; w < WARP_ROWS; ++w) {
    const int microbatch = global_row_idx + w;
    if (microbatch >= microbatches) {
      break;
    }

#pragma unroll
    for (int it = 0; it < WARP_ITERATIONS; it += ELEMENTS_PER_LDG_STG) {
      const int j = col + it * WARP_WIDTH;  // index of the first column
      const int itr_idx = w * cols + it * WARP_WIDTH;

      if (j < cols) {
        output_t out[ELEMENTS_PER_LDG_STG];
#pragma unroll
        for (int element = 0; element < ELEMENTS_PER_LDG_STG; ++element) {
          out[element] = (output_t)(scale * (grad_reg[w][it + element] -
                                             softmax_output_reg[w][it + element] * sum[w]));
        }
        copy_vector<output_t, ELEMENTS_PER_LDG_STG>(gradInput + itr_idx, out);
      }
    }
  }
}

template <typename input_t, typename output_t, typename acc_t, int log2_elements>
void call_kernel_scaled_aligned_causal_masked_softmax_forward(
    dim3 grid_size, dim3 block_size, const int shmem_size, cudaStream_t stream, output_t *dst,
    const input_t *src, const acc_t scale, const int microbatches, const int query_seq_len,
    const int key_seq_len) {
  scaled_aligned_causal_masked_softmax_warp_forward<input_t, output_t, acc_t, log2_elements>
      <<<grid_size, block_size, shmem_size, stream>>>(dst, src, scale, microbatches, query_seq_len,
                                                      key_seq_len);
  NVTE_CHECK_CUDA(cudaGetLastError());
}

template <typename input_t, typename output_t, typename acc_t, int log2_elements>
void call_kernel_scaled_aligned_causal_masked_softmax_backward(
    dim3 grid_size, dim3 block_size, const int shmem_size, cudaStream_t stream, output_t *gradInput,
    const input_t *grad, const input_t *output, const acc_t scale, const int microbatches,
    const int query_seq_len, const int key_seq_len) {
  scaled_aligned_causal_masked_softmax_warp_backward<input_t, output_t, acc_t, log2_elements>
      <<<grid_size, block_size, 0, stream>>>(gradInput, grad, output, scale, microbatches,
                                             query_seq_len, key_seq_len);
  NVTE_CHECK_CUDA(cudaGetLastError());
}

template <typename input_t, typename output_t, typename acc_t>
struct FunctionWrapper {
  using ForwardType =
      std::function<void(dim3 grid_size, dim3 block_size, const int shmem_size, cudaStream_t stream,
                         output_t *dst, const input_t *src, const acc_t scale,
                         const int microbatches, const int query_seq_len, const int key_seq_len)>;
  using BackwardType = std::function<void(
      dim3 grid_size, dim3 block_size, const int shmem_size, cudaStream_t stream,
      output_t *gradInput, const input_t *grad, const input_t *output, const acc_t scale,
      const int microbatches, const int query_seq_len, const int key_seq_len)>;
};

constexpr int MIN_SUPPORTED_POWER = 4;
constexpr int MAX_SUPPORTED_POWER = 14;
constexpr int MIN_POWER = MIN_SUPPORTED_POWER - 1;
constexpr int MAX_POWER = MAX_SUPPORTED_POWER + 1;

// Recursively instantiate the function for the limit of "log2_elements",
// i.e. "MAX_POWER" defined above.
template <typename input_t, typename output_t, typename acc_t, int log2_elements>
struct CompileTimeLoopForward {
  using ForwardFuncType = typename FunctionWrapper<input_t, output_t, acc_t>::ForwardType;
  static void populate(std::array<ForwardFuncType, MAX_POWER> *arr) {
    CompileTimeLoopForward<input_t, output_t, acc_t, log2_elements - 1>::populate(arr);
    (*arr)[log2_elements] =
        &call_kernel_scaled_aligned_causal_masked_softmax_forward<output_t, input_t, acc_t,
                                                                  log2_elements>;
  }
};

template <typename input_t, typename output_t, typename acc_t>
struct CompileTimeLoopForward<input_t, output_t, acc_t, MIN_POWER> {
  using ForwardFuncType = typename FunctionWrapper<input_t, output_t, acc_t>::ForwardType;
  static void populate(std::array<ForwardFuncType, MAX_POWER> *arr) { (*arr)[MIN_POWER] = nullptr; }
};

template <typename input_t, typename output_t, typename acc_t, int log2_elements>
struct CompileTimeLoopBackward {
  using BackwardFuncType = typename FunctionWrapper<input_t, output_t, acc_t>::BackwardType;
  static void populate(std::array<BackwardFuncType, MAX_POWER> *arr) {
    CompileTimeLoopBackward<input_t, output_t, acc_t, log2_elements - 1>::populate(arr);
    (*arr)[log2_elements] =
        &call_kernel_scaled_aligned_causal_masked_softmax_backward<output_t, input_t, acc_t,
                                                                   log2_elements>;
  }
};

template <typename input_t, typename output_t, typename acc_t>
struct CompileTimeLoopBackward<input_t, output_t, acc_t, MIN_POWER> {
  using BackwardFuncType = typename FunctionWrapper<input_t, output_t, acc_t>::BackwardType;
  static void populate(std::array<BackwardFuncType, MAX_POWER> *arr) {
    (*arr)[MIN_POWER] = nullptr;
  }
};

template <typename input_t, typename output_t, typename acc_t>
void dispatch_scaled_aligned_causal_masked_softmax_forward(output_t *dst, const input_t *src,
                                                           const input_t scale, int query_seq_len,
                                                           int key_seq_len, int batches,
                                                           int attn_heads, cudaStream_t stream) {
  NVTE_CHECK(key_seq_len >= 0 && key_seq_len <= 16384, "Unsupported shape.");

  if (key_seq_len == 0) {
    return;
  }
  int log2_elements = log2_ceil(key_seq_len);
  const int next_power_of_two = 1 << log2_elements;

  // This value must match the WARP_WIDTH constexpr
  // value computed inside scaled_aligned_causal_masked_softmax_warp_forward.
  int warp_width = (next_power_of_two < THREADS_PER_WARP) ? next_power_of_two : THREADS_PER_WARP;

  // This value must match the WARP_ROWS constexpr
  // value computed inside scaled_aligned_causal_masked_softmax_warp_forward.
  int microbatches_per_warp = (next_power_of_two <= 128) ? 2 : 1;

  // use 128 threads per block to maximimize gpu utilization
  constexpr int threads_per_block = 128;

  int warps_per_block = threads_per_block / warp_width;
  int microbatches_per_block = warps_per_block * microbatches_per_warp;
  int microbatches = batches * attn_heads * query_seq_len;
  int blocks = DIVUP(microbatches, microbatches_per_block);

  dim3 block_size(warp_width, warps_per_block);
  dim3 grid_size(blocks);

  // create an array of pointers to functions
  using ForwardFuncType = typename FunctionWrapper<input_t, output_t, acc_t>::ForwardType;
  static std::array<ForwardFuncType, MAX_POWER> forwardFunctionArray;
  static bool is_initialized = false;
  if (!is_initialized) {
    CompileTimeLoopForward<input_t, output_t, acc_t, MAX_SUPPORTED_POWER>::populate(
        &forwardFunctionArray);
    is_initialized = true;
  }
  // Call the corresponding kernel
  forwardFunctionArray[log2_elements](grid_size, block_size, 0, stream, dst, src, scale,
                                      microbatches, query_seq_len, key_seq_len);
}

template <typename input_t, typename output_t, typename acc_t>
void dispatch_scaled_aligned_causal_masked_softmax_backward(
    output_t *grad_input, const input_t *grad, const input_t *output, const acc_t scale,
    int query_seq_len, int key_seq_len, int batches, int attn_heads, cudaStream_t stream) {
  NVTE_CHECK(key_seq_len >= 0 && key_seq_len <= 16384, "Unsupported shape.");

  if (key_seq_len == 0) {
    return;
  }
  int log2_elements = log2_ceil(key_seq_len);
  const int next_power_of_two = 1 << log2_elements;

  // This value must match the WARP_WIDTH constexpr
  // value computed inside scaled_aligned_causal_masked_softmax_warp_forward.
  int warp_width = (next_power_of_two < THREADS_PER_WARP) ? next_power_of_two : THREADS_PER_WARP;

  // This value must match the WARP_ROWS constexpr
  // value computed inside scaled_aligned_causal_masked_softmax_warp_forward.
  int microbatches_per_warp = (next_power_of_two <= 128) ? 2 : 1;

  // use 128 threads per block to maximimize gpu utilization
  constexpr int threads_per_block = 128;

  int warps_per_block = threads_per_block / warp_width;
  int microbatches_per_block = warps_per_block * microbatches_per_warp;
  int microbatches = batches * attn_heads * query_seq_len;
  int blocks = DIVUP(microbatches, microbatches_per_block);

  dim3 block_size(warp_width, warps_per_block);
  dim3 grid_size(blocks);

  // create an array of pointers to functions
  using BackwardFuncType = typename FunctionWrapper<input_t, output_t, acc_t>::BackwardType;
  static std::array<BackwardFuncType, MAX_POWER> backwardFunctionArray;
  static bool is_initialized = false;
  if (!is_initialized) {
    CompileTimeLoopBackward<input_t, output_t, acc_t, MAX_SUPPORTED_POWER>::populate(
        &backwardFunctionArray);
    is_initialized = true;
  }
  // Call the corresponding kernel
  backwardFunctionArray[log2_elements](grid_size, block_size, 0, stream, grad_input, grad, output,
                                       scale, microbatches, query_seq_len, key_seq_len);
}

void scaled_aligned_causal_masked_softmax_forward(const Tensor &input, Tensor *softmax_results,
                                                  float scale_factor, cudaStream_t stream) {
  const int batches = input.data.shape[0];
  const int attn_heads = input.data.shape[1];
  const int query_seq_len = input.data.shape[2];
  const int key_seq_len = input.data.shape[3];

  TRANSFORMER_ENGINE_TYPE_SWITCH_16BIT(
      input.data.dtype, softmax_type,
      dispatch_scaled_aligned_causal_masked_softmax_forward<softmax_type, softmax_type, float>(
          reinterpret_cast<softmax_type *>(softmax_results->data.dptr),
          reinterpret_cast<const softmax_type *>(input.data.dptr), scale_factor, query_seq_len,
          key_seq_len, batches, attn_heads, stream););
}

void scaled_aligned_causal_masked_softmax_backward(Tensor output_grads, const Tensor incoming_grads,
                                                   const Tensor softmax_results, float scale_factor,
                                                   cudaStream_t stream) {
  // output grads is a 4d tensor with dimensions [batches, attn_heads, seq_len, seq_len]
  const int batches = output_grads.data.shape[0];
  const int attn_heads = output_grads.data.shape[1];
  const int query_seq_len = output_grads.data.shape[2];
  const int key_seq_len = output_grads.data.shape[3];

  // Softmax Grad
  TRANSFORMER_ENGINE_TYPE_SWITCH_16BIT(
      output_grads.data.dtype, softmax_type,
      dispatch_scaled_aligned_causal_masked_softmax_backward<softmax_type, softmax_type, float>(
          reinterpret_cast<softmax_type *>(output_grads.data.dptr),
          reinterpret_cast<softmax_type const *>(incoming_grads.data.dptr),
          reinterpret_cast<softmax_type const *>(softmax_results.data.dptr), scale_factor,
          query_seq_len, key_seq_len, batches, attn_heads, stream););
}
}  // end namespace transformer_engine

void nvte_scaled_aligned_causal_masked_softmax_forward(const NVTETensor input,
                                                       NVTETensor softmax_results,
                                                       float scale_factor, cudaStream_t stream) {
  NVTE_API_CALL(nvte_scaled_aligned_causal_masked_softmax_forward);
  using namespace transformer_engine;
  scaled_aligned_causal_masked_softmax_forward(*convertNVTETensorCheck(input),
                                               convertNVTETensorCheck(softmax_results),
                                               scale_factor, stream);
}

void nvte_scaled_aligned_causal_masked_softmax_backward(const NVTETensor incoming_grads,
                                                        const NVTETensor softmax_results,
                                                        NVTETensor output_grads, float scale_factor,
                                                        cudaStream_t stream) {
  NVTE_API_CALL(nvte_scaled_aligned_causal_masked_softmax_backward);
  using namespace transformer_engine;
  scaled_aligned_causal_masked_softmax_backward(
      *convertNVTETensorCheck(output_grads), *convertNVTETensorCheck(incoming_grads),
      *convertNVTETensorCheck(softmax_results), scale_factor, stream);
}
