import warnings

import torch
import torch.nn as nn

try:
    from apex.normalization import FusedRMSNorm as RMSNorm
except ImportError:
    warnings.warn("Cannot import apex RMSNorm, switch to vanilla implementation")

    class RMSNorm(torch.nn.Module):
        def __init__(self, dim: int, eps: float = 1e-6):
            """
            Initialize the RMSNorm normalization layer.

            Args:
                dim (int): The dimension of the input tensor.
                eps (float, optional): A small value added to the denominator for numerical stability. Default is 1e-6.

            Attributes:
                eps (float): A small value added to the denominator for numerical stability.
                weight (nn.Parameter): Learnable scaling parameter.

            """
            super().__init__()
            self.eps = eps
            self.weight = nn.Parameter(torch.ones(dim))

        def _norm(self, x):
            """
            Apply the RMSNorm normalization to the input tensor.

            Args:
                x (torch.Tensor): The input tensor.

            Returns:
                torch.Tensor: The normalized tensor.

            """
            return x * torch.rsqrt(x.pow(2).mean(-1, keepdim=True) + self.eps)

        def forward(self, x):
            """
            Forward pass through the RMSNorm layer.

            Args:
                x (torch.Tensor): The input tensor.

            Returns:
                torch.Tensor: The output tensor after applying RMSNorm.

            """
            output = self._norm(x.float()).type_as(x)
            return output * self.weight