import torch
from torch import nn

from detectron2.layers import Conv2d


class _NewEmptyTensorOp(torch.autograd.Function):
    @staticmethod
    def forward(ctx, x, new_shape):
        ctx.shape = x.shape
        return x.new_empty(new_shape)

    @staticmethod
    def backward(ctx, grad):
        shape = ctx.shape
        return _NewEmptyTensorOp.apply(grad, shape), None


class DFConv2d(nn.Module):
    """
    Deformable convolutional layer with configurable
    deformable groups, dilations and groups.

    Code is from:
    https://github.com/facebookresearch/maskrcnn-benchmark/blob/master/maskrcnn_benchmark/layers/misc.py


    """
    def __init__(
            self,
            in_channels,
            out_channels,
            with_modulated_dcn=True,
            kernel_size=3,
            stride=1,
            groups=1,
            dilation=1,
            deformable_groups=1,
            bias=False,
            padding=None
    ):
        super(DFConv2d, self).__init__()
        if isinstance(kernel_size, (list, tuple)):
            assert isinstance(stride, (list, tuple))
            assert isinstance(dilation, (list, tuple))
            assert len(kernel_size) == 2
            assert len(stride) == 2
            assert len(dilation) == 2
            padding = (
                dilation[0] * (kernel_size[0] - 1) // 2,
                dilation[1] * (kernel_size[1] - 1) // 2
            )
            offset_base_channels = kernel_size[0] * kernel_size[1]
        else:
            padding = dilation * (kernel_size - 1) // 2
            offset_base_channels = kernel_size * kernel_size
        if with_modulated_dcn:
            from detectron2.layers.deform_conv import ModulatedDeformConv
            offset_channels = offset_base_channels * 3  # default: 27
            conv_block = ModulatedDeformConv
        else:
            from detectron2.layers.deform_conv import DeformConv
            offset_channels = offset_base_channels * 2  # default: 18
            conv_block = DeformConv
        self.offset = Conv2d(
            in_channels,
            deformable_groups * offset_channels,
            kernel_size=kernel_size,
            stride=stride,
            padding=padding,
            groups=1,
            dilation=dilation
        )
        for l in [self.offset, ]:
            nn.init.kaiming_uniform_(l.weight, a=1)
            torch.nn.init.constant_(l.bias, 0.)
        self.conv = conv_block(
            in_channels,
            out_channels,
            kernel_size=kernel_size,
            stride=stride,
            padding=padding,
            dilation=dilation,
            groups=groups,
            deformable_groups=deformable_groups,
            bias=bias
        )
        self.with_modulated_dcn = with_modulated_dcn
        self.kernel_size = kernel_size
        self.stride = stride
        self.padding = padding
        self.dilation = dilation
        self.offset_split = offset_base_channels * deformable_groups * 2

    def forward(self, x, return_offset=False):
        if x.numel() > 0:
            if not self.with_modulated_dcn:
                offset_mask = self.offset(x)
                x = self.conv(x, offset_mask)
            else:
                offset_mask = self.offset(x)
                offset = offset_mask[:, :self.offset_split, :, :]
                mask = offset_mask[:, self.offset_split:, :, :].sigmoid()
                x = self.conv(x, offset, mask)
            if return_offset:
                return x, offset_mask
            return x
        # get output shape
        output_shape = [
            (i + 2 * p - (di * (k - 1) + 1)) // d + 1
            for i, p, di, k, d in zip(
                x.shape[-2:],
                self.padding,
                self.dilation,
                self.kernel_size,
                self.stride
            )
        ]
        output_shape = [x.shape[0], self.conv.weight.shape[0]] + output_shape
        return _NewEmptyTensorOp.apply(x, output_shape)
