# The implementation is modified from original resent implementaiton, which is
#  also open-sourced by the authors as Yang Liu,
#  and is available publicly on  https://github.com/damo-cv/MogFace

import torch.nn as nn


def conv3x3(in_planes, out_planes, stride=1, groups=1, dilation=1):
    """3x3 convolution with padding"""
    return nn.Conv2d(
        in_planes,
        out_planes,
        kernel_size=3,
        stride=stride,
        padding=dilation,
        groups=groups,
        bias=False,
        dilation=dilation)


def conv1x1(in_planes, out_planes, stride=1):
    """1x1 convolution"""
    return nn.Conv2d(
        in_planes, out_planes, kernel_size=1, stride=stride, bias=False)


class Bottleneck(nn.Module):
    expansion = 4

    def __init__(self,
                 inplanes,
                 planes,
                 stride=1,
                 downsample=None,
                 groups=1,
                 base_width=64,
                 dilation=1,
                 norm_layer=None):
        super(Bottleneck, self).__init__()
        if norm_layer is None:
            norm_layer = nn.BatchNorm2d
        width = int(planes * (base_width / 64.)) * groups
        # Both self.conv2 and self.downsample layers downsample the input when stride != 1
        self.conv1 = conv1x1(inplanes, width)
        self.bn1 = norm_layer(width)
        self.conv2 = conv3x3(width, width, stride, groups, dilation)
        self.bn2 = norm_layer(width)
        self.conv3 = conv1x1(width, planes * self.expansion)
        self.bn3 = norm_layer(planes * self.expansion)
        self.relu = nn.ReLU(inplace=True)
        self.downsample = downsample
        self.stride = stride

    def forward(self, x):
        identity = x

        out = self.conv1(x)
        out = self.bn1(out)
        out = self.relu(out)

        out = self.conv2(out)
        out = self.bn2(out)
        out = self.relu(out)

        out = self.conv3(out)
        out = self.bn3(out)

        if self.downsample is not None:
            identity = self.downsample(x)

        out += identity
        out = self.relu(out)

        return out


class ResNet(nn.Module):

    def __init__(self,
                 depth=50,
                 groups=1,
                 width_per_group=64,
                 replace_stride_with_dilation=None,
                 norm_layer=None,
                 inplanes=64,
                 shrink_ch_ratio=1):
        super(ResNet, self).__init__()
        if norm_layer is None:
            norm_layer = nn.BatchNorm2d
        self._norm_layer = norm_layer

        if depth == 50:
            block = Bottleneck
            layers = [3, 4, 6, 3]
        elif depth == 101:
            block = Bottleneck
            layers = [3, 4, 23, 3]
        elif depth == 152:
            block = Bottleneck
            layers = [3, 4, 36, 3]
        elif depth == 18:
            block = BasicBlock
            layers = [2, 2, 2, 2]
        else:
            raise ValueError('only support depth in [18, 50, 101, 152]')

        shrink_input_ch = int(inplanes * shrink_ch_ratio)
        self.inplanes = int(inplanes * shrink_ch_ratio)
        if shrink_ch_ratio == 0.125:
            layers = [2, 3, 3, 3]

        self.dilation = 1
        if replace_stride_with_dilation is None:
            # each element in the tuple indicates if we should replace
            # the 2x2 stride with a dilated convolution instead
            replace_stride_with_dilation = [False, False, False]
        if len(replace_stride_with_dilation) != 3:
            raise ValueError('replace_stride_with_dilation should be None '
                             'or a 3-element tuple, got {}'.format(
                                 replace_stride_with_dilation))
        self.groups = groups
        self.base_width = width_per_group
        self.conv1 = nn.Conv2d(
            3, self.inplanes, kernel_size=7, stride=2, padding=3, bias=False)
        self.bn1 = norm_layer(self.inplanes)
        self.relu = nn.ReLU(inplace=True)
        self.maxpool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1)
        self.layer1 = self._make_layer(block, shrink_input_ch, layers[0])
        self.layer2 = self._make_layer(
            block,
            shrink_input_ch * 2,
            layers[1],
            stride=2,
            dilate=replace_stride_with_dilation[0])
        self.layer3 = self._make_layer(
            block,
            shrink_input_ch * 4,
            layers[2],
            stride=2,
            dilate=replace_stride_with_dilation[1])
        self.layer4 = self._make_layer(
            block,
            shrink_input_ch * 8,
            layers[3],
            stride=2,
            dilate=replace_stride_with_dilation[2])

    def _make_layer(self, block, planes, blocks, stride=1, dilate=False):
        norm_layer = self._norm_layer
        downsample = None
        previous_dilation = self.dilation
        if dilate:
            self.dilation *= stride
            stride = 1
        if stride != 1 or self.inplanes != planes * block.expansion:
            downsample = nn.Sequential(
                conv1x1(self.inplanes, planes * block.expansion, stride),
                norm_layer(planes * block.expansion),
            )

        layers = []
        layers.append(
            block(self.inplanes, planes, stride, downsample, self.groups,
                  self.base_width, previous_dilation, norm_layer))
        self.inplanes = planes * block.expansion
        for _ in range(1, blocks):
            layers.append(
                block(
                    self.inplanes,
                    planes,
                    groups=self.groups,
                    base_width=self.base_width,
                    dilation=self.dilation,
                    norm_layer=norm_layer))

        return nn.Sequential(*layers)

    def forward(self, x):
        x = self.conv1(x)
        x = self.bn1(x)
        x = self.relu(x)
        x = self.maxpool(x)
        four_conv_layer = []
        x = self.layer1(x)
        four_conv_layer.append(x)
        x = self.layer2(x)
        four_conv_layer.append(x)
        x = self.layer3(x)
        four_conv_layer.append(x)
        x = self.layer4(x)
        four_conv_layer.append(x)

        return four_conv_layer
