import torch


def _cast_if_autocast_enabled(tensor):
    if torch.is_autocast_enabled():
        if tensor.device.type == "cuda":
            dtype = torch.get_autocast_gpu_dtype()
        elif tensor.device.type == "cpu":
            dtype = torch.get_autocast_cpu_dtype()
        else:
            raise NotImplementedError()
        return tensor.to(dtype=dtype)
    return tensor


class LPLayerNorm(torch.nn.LayerNorm):
    def __init__(
        self,
        normalized_shape,
        eps=1e-05,
        elementwise_affine=True,
        device=None,
        dtype=None,
    ):
        super().__init__(
            normalized_shape=normalized_shape,
            eps=eps,
            elementwise_affine=elementwise_affine,
            device=device,
            dtype=dtype,
        )

    def forward(self, x):
        module_device = x.device
        downcast_x = _cast_if_autocast_enabled(x)
        downcast_weight = (
            _cast_if_autocast_enabled(self.weight)
            if self.weight is not None
            else self.weight
        )
        downcast_bias = (
            _cast_if_autocast_enabled(self.bias) if self.bias is not None else self.bias
        )
        with torch.autocast(enabled=False, device_type=module_device.type):
            return torch.nn.functional.layer_norm(
                downcast_x,
                self.normalized_shape,
                downcast_weight,
                downcast_bias,
                self.eps,
            )


def rms_norm(x, weight=None, eps=1e-05):
    output = x / torch.rsqrt(x.pow(2).mean(-1, keepdim=True) + eps)
    if weight is not None:
        return output * weight
    return output


class RMSNorm(torch.nn.Module):
    def __init__(
        self, normalized_shape, eps=1e-05, weight=True, dtype=None, device=None
    ):
        super().__init__()
        self.eps = eps
        if weight:
            self.weight = torch.nn.Parameter(
                torch.ones(normalized_shape, dtype=dtype, device=device)
            )
        else:
            self.register_parameter("weight", None)

    def forward(self, x):
        return rms_norm(x.float(), self.weight, self.eps).to(dtype=x.dtype)


class LPRMSNorm(RMSNorm):
    def __init__(
        self, normalized_shape, eps=1e-05, weight=True, dtype=None, device=None
    ):
        super().__init__(
            normalized_shape=normalized_shape,
            eps=eps,
            weight=weight,
            dtype=dtype,
            device=device,
        )

    def forward(self, x):
        downcast_x = _cast_if_autocast_enabled(x)
        downcast_weight = (
            _cast_if_autocast_enabled(self.weight)
            if self.weight is not None
            else self.weight
        )
        with torch.autocast(enabled=False, device_type=x.device.type):
            return rms_norm(downcast_x, downcast_weight, self.eps).to(dtype=x.dtype)


NORM_CLASS_REGISTRY = {
    "layernorm": torch.nn.LayerNorm,
    "low_precision_layernorm": LPLayerNorm,
    "rmsnorm": RMSNorm,
    "low_precision_rmsnorm": LPRMSNorm,
}