import torch

try:
    import fused_mix_prec_layer_norm_cuda
except:
    fused_mix_prec_layer_norm_cuda = None


class FusedLayerNormAffineFunction1D(torch.autograd.Function):
  r"""
  Layernorm

  :param input: input maxtrix
  :param weight: weight matrix
  :param bias: bias matrix
  :param normalized_shape: input shape from an expected input
        of size. :math:`[* \times \text{normalized_shape}[0] \times \text{normalized_shape}[1] \times \ldots \times \text{normalized_shape}[-1]]`
        If a single integer is used, it is treated as a singleton list, and this module will
        normalize over the last dimension which is expected to be of that specific size.
  :param eps: a value added to the denominator for numerical stability
  """

  @staticmethod
  def forward(ctx, input, weight, bias, normalized_shape, eps):
    ctx.normalized_shape = normalized_shape
    ctx.eps = eps
    input_ = input.contiguous()
    weight_ = weight.contiguous()
    bias_ = bias.contiguous()
    output, mean, invvar = fused_mix_prec_layer_norm_cuda.forward_affine(
        input_, ctx.normalized_shape, weight_, bias_, ctx.eps)
    ctx.save_for_backward(input_, weight_, bias_, mean, invvar)
    return output


  @staticmethod
  def backward(ctx, grad_output):
    input_, weight_, bias_, mean, invvar = ctx.saved_tensors
    grad_input = grad_weight = grad_bias = None
    grad_input, grad_weight, grad_bias \
      = fused_mix_prec_layer_norm_cuda.backward_affine(
        grad_output.contiguous(), mean, invvar,
        input_, ctx.normalized_shape,
        weight_, bias_, ctx.eps)

    return grad_input, grad_weight, grad_bias, None, None