# Code adapted from: https://github.com/Cadene/pretrained-models.pytorch
import math
from collections import OrderedDict
from itertools import chain

import torch.nn as nn
from torch.utils import model_zoo

from utils import Flatten


class SEModule(nn.Module):
    def __init__(self, channels, reduction):
        super(SEModule, self).__init__()
        self.avg_pool = nn.AdaptiveAvgPool2d(1)
        self.fc1 = nn.Conv2d(channels, channels // reduction, kernel_size=1, padding=0)
        self.relu = nn.ReLU(inplace=True)
        self.fc2 = nn.Conv2d(channels // reduction, channels, kernel_size=1, padding=0)
        self.sigmoid = nn.Sigmoid()

    def forward(self, x):
        module_input = x
        x = self.avg_pool(x)
        x = self.fc1(x)
        x = self.relu(x)
        x = self.fc2(x)
        x = self.sigmoid(x)
        return module_input * x


class SEResNeXtBottleneck(nn.Module):
    """
    ResNeXt bottleneck type C with a Squeeze-and-Excitation module.
    """
    expansion = 4

    def __init__(self, inplanes, planes, groups, reduction, stride=1, downsample=None, base_width=4):
        super(SEResNeXtBottleneck, self).__init__()
        width = math.floor(planes * (base_width / 64)) * groups
        self.conv1 = nn.Conv2d(inplanes, width, kernel_size=1, bias=False, stride=1)
        self.bn1 = nn.BatchNorm2d(width)
        self.conv2 = nn.Conv2d(width, width, kernel_size=3, stride=stride, padding=1, groups=groups, bias=False)
        self.bn2 = nn.BatchNorm2d(width)
        self.conv3 = nn.Conv2d(width, planes * 4, kernel_size=1, bias=False)
        self.bn3 = nn.BatchNorm2d(planes * 4)
        self.relu = nn.ReLU(inplace=True)
        self.se_module = SEModule(planes * 4, reduction=reduction)
        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 = self.se_module(out) + residual
        out = self.relu(out)

        return out


class SENet(nn.Module):
    def __init__(self, block, layers, groups, reduction, inplanes=128,
                 downsample_kernel_size=3, downsample_padding=1):
        super(SENet, self).__init__()
        self.inplanes = inplanes

        layer0_modules = [
            ('conv1', nn.Conv2d(3, inplanes, kernel_size=7, stride=2, padding=3, bias=False)),
            ('bn1', nn.BatchNorm2d(inplanes)),
            ('relu1', nn.ReLU(inplace=True)),
            # To preserve compatibility with Caffe weights `ceil_mode=True`
            # is used instead of `padding=1`.
            ('pool', nn.MaxPool2d(3, stride=2, ceil_mode=True))
        ]
        self.layer0 = nn.Sequential(OrderedDict(layer0_modules))
        self.layer1 = self._make_layer(
            block,
            planes=64,
            blocks=layers[0],
            groups=groups,
            reduction=reduction,
            downsample_kernel_size=1,
            downsample_padding=0
        )
        self.layer2 = self._make_layer(
            block,
            planes=128,
            blocks=layers[1],
            stride=2,
            groups=groups,
            reduction=reduction,
            downsample_kernel_size=downsample_kernel_size,
            downsample_padding=downsample_padding
        )
        self.layer3 = self._make_layer(
            block,
            planes=256,
            blocks=layers[2],
            stride=2,
            groups=groups,
            reduction=reduction,
            downsample_kernel_size=downsample_kernel_size,
            downsample_padding=downsample_padding
        )
        self.layer4 = self._make_layer(
            block,
            planes=512,
            blocks=layers[3],
            stride=2,
            groups=groups,
            reduction=reduction,
            downsample_kernel_size=downsample_kernel_size,
            downsample_padding=downsample_padding
        )
        self.cls = nn.Sequential(
            nn.AdaptiveAvgPool2d(1),
            Flatten(),
            nn.Linear(512 * block.expansion, 1)
        )

    def _make_layer(self, block, planes, blocks, groups, reduction, stride=1,
                    downsample_kernel_size=1, downsample_padding=0):
        downsample = None
        if stride != 1 or self.inplanes != planes * block.expansion:
            downsample = nn.Sequential(
                nn.Conv2d(self.inplanes, planes * block.expansion,
                          kernel_size=downsample_kernel_size, stride=stride,
                          padding=downsample_padding, bias=False),
                nn.BatchNorm2d(planes * block.expansion),
            )

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

        return nn.Sequential(*layers)

    def paramgroup01(self):
        return chain(
            self.layer0.parameters(),
            self.layer1.parameters(),
        )

    def paramgroup234(self):
        return chain(
            self.layer2.parameters(),
            self.layer3.parameters(),
            self.layer4.parameters(),
        )

    def parameters_classifier(self):
        return self.cls.parameters()

    def forward(self, x):
        x = self.layer0(x)
        x = self.layer1(x)
        x = self.layer2(x)
        x = self.layer3(x)
        x = self.layer4(x)
        c = self.cls(x)
        return c


def get_model():
    model = SENet(SEResNeXtBottleneck, [3, 4, 6, 3], groups=32, reduction=16, inplanes=64,
                  downsample_kernel_size=1, downsample_padding=0)
    checkpoint = model_zoo.load_url('http://data.lip6.fr/cadene/pretrainedmodels/se_resnext50_32x4d-a260b3a4.pth')
    model.load_state_dict(checkpoint, strict=False)
    return model