# Originated from https://github.com/NVIDIA/DeepLearningExamples/tree/master/PyTorch/Classification/RN50v1.5
# now code is at https://github.com/NVIDIA/DeepLearningExamples/tree/master/PyTorch/Classification/ConvNets
import torch.nn as nn

__all__ = ['ResNet', 'build_resnet', 'resnet_versions', 'resnet_configs']

# ResNetBuilder {{{


class ResNetBuilder(object):
    def __init__(self, version, config):
        self.config = config

        self.L = sum(version['layers'])
        self.M = version['block'].M

        self.layer_index = 0

    def conv(self, kernel_size, in_planes, out_planes, stride=1):
        if kernel_size == 3:
            conv = self.config['conv'](
                in_planes,
                out_planes,
                kernel_size=3,
                stride=stride,
                padding=1,
                bias=False,
            )
        elif kernel_size == 1:
            conv = nn.Conv2d(
                in_planes, out_planes, kernel_size=1, stride=stride, bias=False
            )
        elif kernel_size == 5:
            conv = nn.Conv2d(
                in_planes,
                out_planes,
                kernel_size=5,
                stride=stride,
                padding=2,
                bias=False,
            )
        elif kernel_size == 7:
            conv = nn.Conv2d(
                in_planes,
                out_planes,
                kernel_size=7,
                stride=stride,
                padding=3,
                bias=False,
            )
        else:
            return None

        if self.config['nonlinearity'] == 'relu':
            nn.init.kaiming_normal_(
                conv.weight,
                mode=self.config['conv_init'],
                nonlinearity=self.config['nonlinearity'],
            )

        return conv

    def conv3x3(self, in_planes, out_planes, stride=1):
        """3x3 convolution with padding"""
        c = self.conv(3, in_planes, out_planes, stride=stride)
        return c

    def conv1x1(self, in_planes, out_planes, stride=1):
        """1x1 convolution with padding"""
        c = self.conv(1, in_planes, out_planes, stride=stride)
        return c

    def conv7x7(self, in_planes, out_planes, stride=1):
        """7x7 convolution with padding"""
        c = self.conv(7, in_planes, out_planes, stride=stride)
        return c

    def conv5x5(self, in_planes, out_planes, stride=1):
        """5x5 convolution with padding"""
        c = self.conv(5, in_planes, out_planes, stride=stride)
        return c

    def batchnorm(self, planes, last_bn=False):
        bn = nn.BatchNorm2d(planes)
        gamma_init_val = 0 if last_bn and self.config['last_bn_0_init'] else 1
        nn.init.constant_(bn.weight, gamma_init_val)
        nn.init.constant_(bn.bias, 0)

        return bn

    def activation(self):
        return self.config['activation']()


# ResNetBuilder }}}


# BasicBlock {{{
class BasicBlock(nn.Module):
    M = 2
    expansion = 1

    def __init__(self, builder, inplanes, planes, stride=1, downsample=None):
        super(BasicBlock, self).__init__()
        self.conv1 = builder.conv3x3(inplanes, planes, stride)
        self.bn1 = builder.batchnorm(planes)
        self.relu = builder.activation()
        self.conv2 = builder.conv3x3(planes, planes)
        self.bn2 = builder.batchnorm(planes, last_bn=True)
        self.downsample = downsample
        self.stride = stride

    def forward(self, x):
        residual = x

        out = self.conv1(x)
        if self.bn1 is not None:
            out = self.bn1(out)

        out = self.relu(out)

        out = self.conv2(out)

        if self.bn2 is not None:
            out = self.bn2(out)

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

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

        return out


# BasicBlock }}}


# Bottleneck {{{
class Bottleneck(nn.Module):
    M = 3
    expansion = 4

    def __init__(self, builder, inplanes, planes, stride=1, downsample=None):
        super(Bottleneck, self).__init__()
        self.conv1 = builder.conv1x1(inplanes, planes)
        self.bn1 = builder.batchnorm(planes)
        self.conv2 = builder.conv3x3(planes, planes, stride=stride)
        self.bn2 = builder.batchnorm(planes)
        self.conv3 = builder.conv1x1(planes, planes * self.expansion)
        self.bn3 = builder.batchnorm(planes * self.expansion, last_bn=True)
        self.relu = builder.activation()
        self.downsample = downsample
        self.stride = stride

    def forward(self, x):
        residual = 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:
            residual = self.downsample(x)

        out += residual

        out = self.relu(out)

        return out


# Bottleneck }}}


# ResNet {{{
class ResNet(nn.Module):
    def __init__(self, builder, block, layers, num_classes=1000):
        self.inplanes = 64
        super(ResNet, self).__init__()
        self.conv1 = builder.conv7x7(3, 64, stride=2)
        self.bn1 = builder.batchnorm(64)
        self.relu = builder.activation()
        self.maxpool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1)
        self.layer1 = self._make_layer(builder, block, 64, layers[0])
        self.layer2 = self._make_layer(builder, block, 128, layers[1], stride=2)
        self.layer3 = self._make_layer(builder, block, 256, layers[2], stride=2)
        self.layer4 = self._make_layer(builder, block, 512, layers[3], stride=2)
        self.avgpool = nn.AdaptiveAvgPool2d(1)
        self.fc = nn.Linear(512 * block.expansion, num_classes)

    def _make_layer(self, builder, block, planes, blocks, stride=1):
        downsample = None
        if stride != 1 or self.inplanes != planes * block.expansion:
            dconv = builder.conv1x1(
                self.inplanes, planes * block.expansion, stride=stride
            )
            dbn = builder.batchnorm(planes * block.expansion)
            if dbn is not None:
                downsample = nn.Sequential(dconv, dbn)
            else:
                downsample = dconv

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

        builder.layer_index += 1

        return nn.Sequential(*layers)

    def forward(self, x):
        x = self.conv1(x)
        if self.bn1 is not None:
            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


# ResNet }}}


resnet_configs = {
    'classic': {
        'conv': nn.Conv2d,
        'conv_init': 'fan_out',
        'nonlinearity': 'relu',
        'last_bn_0_init': False,
        'activation': lambda: nn.ReLU(inplace=True),
    },
    'fanin': {
        'conv': nn.Conv2d,
        'conv_init': 'fan_in',
        'nonlinearity': 'relu',
        'last_bn_0_init': False,
        'activation': lambda: nn.ReLU(inplace=True),
    },
}

resnet_versions = {
    'resnet18': {
        'net': ResNet,
        'block': BasicBlock,
        'layers': [2, 2, 2, 2],
        'num_classes': 1000,
    },
    'resnet34': {
        'net': ResNet,
        'block': BasicBlock,
        'layers': [3, 4, 6, 3],
        'num_classes': 1000,
    },
    'resnet50': {
        'net': ResNet,
        'block': Bottleneck,
        'layers': [3, 4, 6, 3],
        'num_classes': 1000,
    },
    'resnet101': {
        'net': ResNet,
        'block': Bottleneck,
        'layers': [3, 4, 23, 3],
        'num_classes': 1000,
    },
    'resnet152': {
        'net': ResNet,
        'block': Bottleneck,
        'layers': [3, 8, 36, 3],
        'num_classes': 1000,
    },
}


def build_resnet(version, config, model_state=None):
    version = resnet_versions[version]
    config = resnet_configs[config]

    builder = ResNetBuilder(version, config)
    print("Version: {}".format(version))
    print("Config: {}".format(config))
    model = version['net'](
        builder, version['block'], version['layers'], version['num_classes']
    )

    return model
