# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.

import torch
import torch.nn as nn
import torch.nn.functional as F
from torch import Tensor, Size
from torch.cuda.amp import autocast


__all__ = ["LayerNorm"]

try:
    from apex.normalization import FusedLayerNorm as _FusedLayerNorm

    has_fused_layernorm = True

    class FusedLayerNorm(_FusedLayerNorm):
        @torch.jit.unused
        def forward(self, x):
            if not x.is_cuda:
                return super().forward(x)
            else:
                with torch.cuda.device(x.device):
                    return super().forward(x)

except ImportError:
    has_fused_layernorm = False


def LayerNorm(normalized_shape, eps=1e-5, elementwise_affine=True, export=False):
    if torch.jit.is_scripting():
        export = True
    if not export and torch.cuda.is_available() and has_fused_layernorm:
        return FusedLayerNorm(normalized_shape, eps, elementwise_affine)
    else:
        return torch.nn.LayerNorm(normalized_shape, eps, elementwise_affine)
    return torch.nn.LayerNorm(normalized_shape, eps, elementwise_affine)

class FP16LayerNorm(torch.nn.LayerNorm):

    def forward(self, input):
        with autocast(enabled=False):
            return F.layer_norm(input.half(), self.normalized_shape, self.weight.half(), self.bias.half(), self.eps)