import torch
import torch.nn as nn
import math
import torch.utils.model_zoo as model_zoo
from torch.nn import functional as F


__all__ = ['ResNet', 'resnet50', 'resnet101', 'resnet152']


model_urls = {
    'resnet50': 'https://download.pytorch.org/models/resnet50-19c8e357.pth',
    'resnet101': 'https://download.pytorch.org/models/resnet101-5d3b4d8f.pth',
    'resnet152': 'https://download.pytorch.org/models/resnet152-b121ed2d.pth',
}


class ASPP(nn.Module):

    def __init__(self, C, depth, num_classes, conv=nn.Conv2d, norm=nn.BatchNorm2d, momentum=0.0003, mult=1):
        super(ASPP, self).__init__()
        self._C = C
        self._depth = depth
        self._num_classes = num_classes

        self.global_pooling = nn.AdaptiveAvgPool2d(1)
        self.relu = nn.ReLU(inplace=True)
        self.aspp1 = conv(C, depth, kernel_size=1, stride=1, bias=False)
        self.aspp2 = conv(C, depth, kernel_size=3, stride=1,
                               dilation=int(6*mult), padding=int(6*mult),
                               bias=False)
        self.aspp3 = conv(C, depth, kernel_size=3, stride=1,
                               dilation=int(12*mult), padding=int(12*mult),
                               bias=False)
        self.aspp4 = conv(C, depth, kernel_size=3, stride=1,
                               dilation=int(18*mult), padding=int(18*mult),
                               bias=False)
        self.aspp5 = conv(C, depth, kernel_size=1, stride=1, bias=False)
        self.aspp1_bn = norm(depth, momentum)
        self.aspp2_bn = norm(depth, momentum)
        self.aspp3_bn = norm(depth, momentum)
        self.aspp4_bn = norm(depth, momentum)
        self.aspp5_bn = norm(depth, momentum)
        self.conv2 = conv(depth * 5, depth, kernel_size=1, stride=1,
                               bias=False)
        self.bn2 = norm(depth, momentum)
        self.dropout = nn.Dropout(0.5)

    def forward(self, x):
        x1 = self.aspp1(x)
        x1 = self.aspp1_bn(x1)
        x1 = self.relu(x1)
        x2 = self.aspp2(x)
        x2 = self.aspp2_bn(x2)
        x2 = self.relu(x2)
        x3 = self.aspp3(x)
        x3 = self.aspp3_bn(x3)
        x3 = self.relu(x3)
        x4 = self.aspp4(x)
        x4 = self.aspp4_bn(x4)
        x4 = self.relu(x4)
        x5 = self.global_pooling(x)
        x5 = self.aspp5(x5)
        x5 = self.aspp5_bn(x5)
        x5 = self.relu(x5)
        x5 = nn.Upsample((x.shape[2], x.shape[3]), mode='bilinear',
                         align_corners=True)(x5)
        x = torch.cat((x1, x2, x3, x4, x5), 1)
        x = self.conv2(x)
        x = self.bn2(x)
        x = self.relu(x)
        x = self.dropout(x)

        return x


class Bottleneck(nn.Module):
    expansion = 4

    def __init__(self, inplanes, planes, stride=1, downsample=None, dilation=1, conv=None, norm=None):
        super(Bottleneck, self).__init__()
        self.conv1 = conv(inplanes, planes, kernel_size=1, bias=False)
        self.bn1 = norm(planes)
        self.conv2 = conv(planes, planes, kernel_size=3, stride=stride,
                               dilation=dilation, padding=dilation, bias=False)
        self.bn2 = norm(planes)
        self.conv3 = conv(planes, planes * self.expansion, kernel_size=1, bias=False)
        self.bn3 = norm(planes * self.expansion)
        self.relu = nn.ReLU(inplace=True)
        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

    
class Decoder(nn.Module):
    def __init__(self, low_level_inplanes, num_classes, conv=nn.Conv2d, norm=nn.BatchNorm2d, momentum=0.0003):
        super(Decoder, self).__init__()
        
        self.relu = nn.ReLU(inplace=True)
        self.conv1 = conv(low_level_inplanes, 48, 1, stride=1, bias=False)
        self.bn1 = norm(48, momentum)
        self.last_conv = nn.Sequential(conv(304, 256, kernel_size=3, stride=1, padding=1, bias=False),
                                       norm(256, momentum),
                                       nn.ReLU(),
                                       nn.Dropout(0.5),
                                       conv(256, 256, kernel_size=3, stride=1, padding=1, bias=False),
                                       norm(256, momentum),
                                       nn.ReLU(),
                                       nn.Dropout(0.1),
                                       conv(256, num_classes, kernel_size=1, stride=1))
        
    def forward(self, x, low_level_feat):
        low_level_feat = self.conv1(low_level_feat)
        low_level_feat = self.bn1(low_level_feat)
        low_level_feat = self.relu(low_level_feat)

        x = F.interpolate(x, size=low_level_feat.size()[2:], mode='bilinear', align_corners=True)
        x = torch.cat((x, low_level_feat), dim=1)
        x = self.last_conv(x)
        
        return x
    
class ResNetPlus(nn.Module):

    def __init__(self, block, layers, num_classes, num_subtypes=0):
        self.inplanes = 64
        self.norm = lambda planes, momentum=0.05: nn.BatchNorm2d(planes, momentum=momentum)
        self.conv = nn.Conv2d
        self.num_subtypes = num_subtypes

        super(ResNetPlus, self).__init__()
        self.conv1 = self.conv(3, 64, kernel_size=7, stride=2, padding=3,bias=False)
        self.bn1 = self.norm(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=1,
                                       dilation=2)
        self.aspp = ASPP(512 * block.expansion, 256, num_classes, conv=self.conv, norm=self.norm)
        self.decoder = Decoder(256, num_classes, conv=self.conv, norm=self.norm)
        
        if self.num_subtypes>0:
            self.classifier = nn.Sequential(
                nn.AdaptiveAvgPool2d(1),
                self.conv(512 * block.expansion, self.num_subtypes, kernel_size=1))

        for m in self.modules():
            if isinstance(m, self.conv):
                n = m.kernel_size[0] * m.kernel_size[1] * m.out_channels
                m.weight.data.normal_(0, math.sqrt(2. / n))
            elif isinstance(m, nn.BatchNorm2d):
                m.weight.data.fill_(1)
                m.bias.data.zero_()

    def _make_layer(self, block, planes, blocks, stride=1, dilation=1):
        downsample = None
        if stride != 1 or dilation != 1 or self.inplanes != planes * block.expansion:
            downsample = nn.Sequential(
                self.conv(self.inplanes, planes * block.expansion,
                          kernel_size=1, stride=stride, dilation=max(1, dilation/2), bias=False),
                self.norm(planes * block.expansion),
            )

        layers = []
        layers.append(block(self.inplanes, planes, stride, downsample, dilation=max(1, dilation/2), conv=self.conv, norm=self.norm))
        self.inplanes = planes * block.expansion
        for i in range(1, blocks):
            layers.append(block(self.inplanes, planes, dilation=dilation, conv=self.conv, norm=self.norm))

        return nn.Sequential(*layers)

    def forward(self, x):
        input_size = (x.shape[2], x.shape[3])
        x = self.conv1(x)
        x = self.bn1(x)
        x = self.relu(x)
        x = self.maxpool(x)

        x = self.layer1(x)
        low_level_feat = x
        x = self.layer2(x)
        x = self.layer3(x)
        x = self.layer4(x)
        if self.num_subtypes > 0:
            y = self.classifier(x)

        x = self.aspp(x)
        x = self.decoder(x, low_level_feat)
        
        x = F.interpolate(x, size=input_size, mode='bilinear', align_corners=True)
        
        if self.num_subtypes > 0:
            return x,y
        
        return x


def resnet50(pretrained=False, **kwargs):
    """Constructs a ResNet-50 model.

    Args:
        pretrained (bool): If True, returns a model pre-trained on ImageNet
    """
    model = ResNetPlus(Bottleneck, [3, 4, 6, 3], **kwargs)
    if pretrained:
        model.load_state_dict(model_zoo.load_url(model_urls['resnet50']))
    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 = ResNetPlus(Bottleneck, [3, 4, 23, 3], **kwargs)
    if pretrained:
        model_dict = model.state_dict()
        pretrained_dict = model_zoo.load_url(model_urls['resnet101'])
        overlap_dict = {k: v for k, v in pretrained_dict.items() if k in model_dict}
        model_dict.update(overlap_dict)
        model.load_state_dict(model_dict)
        
    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 = ResNetPlus(Bottleneck, [3, 8, 36, 3], **kwargs)
    if pretrained:
        model.load_state_dict(model_zoo.load_url(model_urls['resnet152']))
    return model
