from distutils.version import LooseVersion

import torch
import torch.nn as nn
import torch.nn.functional as F

from mmcv.utils import TORCH_VERSION, build_from_cfg
from .registry import ACTIVATION_LAYERS

for module in [
        nn.ReLU, nn.LeakyReLU, nn.PReLU, nn.RReLU, nn.ReLU6, nn.ELU,
        nn.Sigmoid, nn.Tanh
]:
    ACTIVATION_LAYERS.register_module(module=module)


@ACTIVATION_LAYERS.register_module(name='Clip')
@ACTIVATION_LAYERS.register_module()
class Clamp(nn.Module):
    """Clamp activation layer.

    This activation function is to clamp the feature map value within
    :math:`[min, max]`. More details can be found in ``torch.clamp()``.

    Args:
        min (Number | optional): Lower-bound of the range to be clamped to.
            Default to -1.
        max (Number | optional): Upper-bound of the range to be clamped to.
            Default to 1.
    """

    def __init__(self, min=-1., max=1.):
        super(Clamp, self).__init__()
        self.min = min
        self.max = max

    def forward(self, x):
        """Forward function.

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

        Returns:
            torch.Tensor: Clamped tensor.
        """
        return torch.clamp(x, min=self.min, max=self.max)


class GELU(nn.Module):
    r"""Applies the Gaussian Error Linear Units function:

    .. math::
        \text{GELU}(x) = x * \Phi(x)
    where :math:`\Phi(x)` is the Cumulative Distribution Function for
    Gaussian Distribution.

    Shape:
        - Input: :math:`(N, *)` where `*` means, any number of additional
          dimensions
        - Output: :math:`(N, *)`, same shape as the input

    .. image:: scripts/activation_images/GELU.png

    Examples::

        >>> m = nn.GELU()
        >>> input = torch.randn(2)
        >>> output = m(input)
    """

    def forward(self, input):
        return F.gelu(input)


if (TORCH_VERSION == 'parrots'
        or LooseVersion(TORCH_VERSION) < LooseVersion('1.4')):
    ACTIVATION_LAYERS.register_module(module=GELU)
else:
    ACTIVATION_LAYERS.register_module(module=nn.GELU)


def build_activation_layer(cfg):
    """Build activation layer.

    Args:
        cfg (dict): The activation layer config, which should contain:
            - type (str): Layer type.
            - layer args: Args needed to instantiate an activation layer.

    Returns:
        nn.Module: Created activation layer.
    """
    return build_from_cfg(cfg, ACTIVATION_LAYERS)
