import torch
import torch.nn as nn

__all__ = ['resnet50']

class PSConv2d(nn.Module):
    def __init__(self, in_channels, out_channels, kernel_size=3, stride=1, padding=1, dilation=2, parts=4, bias=False):
        super(PSConv2d, self).__init__()
        self.gwconv = nn.Conv2d(in_channels, out_channels, kernel_size, stride, dilation, dilation, groups=parts, bias=bias)
        self.gwconv_shift = nn.Conv2d(in_channels, out_channels, kernel_size, stride, 2 * dilation, 2 * dilation, groups=parts, bias=bias)
        self.conv = nn.Conv2d(in_channels, out_channels, kernel_size, stride, padding, bias=bias)

        def backward_hook(grad):
            out = grad.clone()
            out[self.mask] = 0
            return out

        # self.mask = torch.zeros(self.conv.weight.shape).byte().cuda()
        self.mask = torch.zeros(self.conv.weight.shape).byte()

        _in_channels = in_channels // parts
        _out_channels = out_channels // parts
        for i in range(parts):
            self.mask[i * _out_channels: (i + 1) * _out_channels, i * _in_channels: (i + 1) * _in_channels, : , :] = 1
            self.mask[(i + parts//2)%parts * _out_channels: ((i + parts//2)%parts + 1) * _out_channels, i * _in_channels: (i + 1) * _in_channels, :, :] = 1
        self.conv.weight.data[self.mask] = 0
        self.conv.weight.register_hook(backward_hook)

    def forward(self, x):
        x1, x2 = x.chunk(2, dim=1)
        x_shift = self.gwconv_shift(torch.cat((x2, x1), dim=1))
        return self.gwconv(x) + self.conv(x) + x_shift


# PSConv-based Group Convolution
class PSGConv2d(nn.Module):
    def __init__(self, in_channels, out_channels, kernel_size=3, stride=1, padding=1, dilation=2, groups=4, parts=4, bias=False):
        super(PSGConv2d, self).__init__()
        self.gwconv = nn.Conv2d(in_channels, out_channels, kernel_size, stride, dilation, dilation, groups=groups * parts, bias=bias)
        self.gwconv_shift = nn.Conv2d(in_channels, out_channels, kernel_size, stride, 2 * dilation, 2 * dilation, groups=groups * parts, bias=bias)
        self.conv = nn.Conv2d(in_channels, out_channels, kernel_size, stride, padding, groups=groups, bias=bias)

        def backward_hook(grad):
            out = grad.clone()
            out[self.mask] = 0
            return out

        # self.mask = torch.zeros(self.conv.weight.shape).byte().cuda()
        self.mask = torch.zeros(self.conv.weight.shape).byte()

        _in_channels = in_channels // (groups * parts)
        _out_channels = out_channels // (groups * parts)
        for i in range(parts):
            for j in range(groups):
                self.mask[(i + j * groups) * _out_channels: (i + j * groups + 1) * _out_channels, i * _in_channels: (i + 1) * _in_channels, : , :] = 1
                self.mask[((i + parts // 2) % parts + j * groups) * _out_channels: ((i + parts // 2) % parts + j * groups + 1) * _out_channels, i * _in_channels: (i + 1) * _in_channels, :, :] = 1
        self.conv.weight.data[self.mask] = 0
        self.conv.weight.register_hook(backward_hook)
        self.groups = groups

    def forward(self, x):
        x_split = (z.chunk(2, dim=1) for z in x.chunk(self.groups, dim=1))
        x_merge = torch.cat(tuple(torch.cat((x2, x1), dim=1) for (x1, x2) in x_split), dim=1)
        x_shift = self.gwconv_shift(x_merge)
        return self.gwconv(x) + self.conv(x) + x_shift



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


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 BasicBlock(nn.Module):
    expansion = 1

    def __init__(self, inplanes, planes, stride=1, downsample=None):
        super(BasicBlock, self).__init__()
        self.conv1 = PSConv2d(inplanes, planes, stride)
        self.bn1 = nn.BatchNorm2d(planes)
        self.relu = nn.ReLU(inplace=True)
        self.conv2 = PSConv2d(planes, planes)
        self.bn2 = nn.BatchNorm2d(planes)
        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)

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

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

        return out


class Bottleneck(nn.Module):
    expansion = 4

    def __init__(self, inplanes, planes, stride=1, downsample=None):
        super(Bottleneck, self).__init__()
        self.conv1 = conv1x1(inplanes, planes)
        self.bn1 = nn.BatchNorm2d(planes)
        self.conv2 = PSConv2d(planes, planes, stride=stride)
        self.bn2 = nn.BatchNorm2d(planes)
        self.conv3 = conv1x1(planes, planes * self.expansion)
        self.bn3 = nn.BatchNorm2d(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, block, layers, num_classes=365, zero_init_residual=False):
        super(ResNet, self).__init__()
        self.inplanes = 64
        self.conv1 = nn.Conv2d(3, 64, kernel_size=7, stride=2, padding=3,
                               bias=False)
        self.bn1 = nn.BatchNorm2d(64)
        self.relu = nn.ReLU(inplace=True)
        self.maxpool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1)
        self.layer1 = self._make_layer(block, 64, layers[0])
        self.layer2 = self._make_layer(block, 128, layers[1], stride=2)
        self.layer3 = self._make_layer(block, 256, layers[2], stride=2)
        self.layer4 = self._make_layer(block, 512, layers[3], stride=2)
        self.avgpool = nn.AdaptiveAvgPool2d((1, 1))
        self.fc = nn.Linear(512 * block.expansion, num_classes)

        for m in self.modules():
            if isinstance(m, nn.Conv2d):
                nn.init.kaiming_normal_(m.weight, mode='fan_out', nonlinearity='relu')
            elif isinstance(m, nn.BatchNorm2d):
                nn.init.constant_(m.weight, 1)
                nn.init.constant_(m.bias, 0)

        # Zero-initialize the last BN in each residual branch,
        # so that the residual branch starts with zeros, and each residual block behaves like an identity.
        # This improves the model by 0.2~0.3% according to https://arxiv.org/abs/1706.02677
        if zero_init_residual:
            for m in self.modules():
                if isinstance(m, Bottleneck):
                    nn.init.constant_(m.bn3.weight, 0)
                elif isinstance(m, BasicBlock):
                    nn.init.constant_(m.bn2.weight, 0)

    def _make_layer(self, block, planes, blocks, stride=1):
        downsample = None
        if stride != 1 or self.inplanes != planes * block.expansion:
            downsample = nn.Sequential(
                conv1x1(self.inplanes, planes * block.expansion, stride),
                nn.BatchNorm2d(planes * block.expansion),
            )

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

        return nn.Sequential(*layers)

    def forward(self, x):
        x = self.conv1(x)
        x = self.bn1(x)
        x = self.relu(x)
        x = self.maxpool(x)

        x = self.layer1(x)
        x = self.layer2(x)
        x = self.layer3(x)
        x = self.layer4(x)

        x = self.avgpool(x)
        x = x.view(x.size(0), -1)
        x = self.fc(x)

        return x


def resnet18(pretrained=False, **kwargs):
    """Constructs a ResNet-18 model.
    Args:
        pretrained (bool): If True, returns a model pre-trained on ImageNet
    """
    model = ResNet(BasicBlock, [2, 2, 2, 2], **kwargs)
    return model


def resnet34(pretrained=False, **kwargs):
    """Constructs a ResNet-34 model.
    Args:
        pretrained (bool): If True, returns a model pre-trained on ImageNet
    """
    model = ResNet(BasicBlock, [3, 4, 6, 3], **kwargs)
    return model


def resnet50(pretrained=False, **kwargs):
    """Constructs a ResNet-50 model.
    Args:
        pretrained (bool): If True, returns a model pre-trained on ImageNet
    """
    model = ResNet(Bottleneck, [3, 4, 6, 3], **kwargs)
    return model


def resnet101(pretrained=False, **kwargs):
    """Constructs a ResNet-101 model.
    Args:
        pretrained (bool): If True, returns a model pre-trained on ImageNet
    """
    model = ResNet(Bottleneck, [3, 4, 23, 3], **kwargs)
    return model


def resnet152(pretrained=False, **kwargs):
    """Constructs a ResNet-152 model.
    Args:
        pretrained (bool): If True, returns a model pre-trained on ImageNet
    """
    model = ResNet(Bottleneck, [3, 8, 36, 3], **kwargs)
    return model


def demo():
    from torchstat import stat
    net = resnet50(num_classes=365)
    y = net(torch.randn(5, 3, 224, 224))
    print(y.size())
    stat(net, (3, 224, 224))

# demo()
