"""SENet in PyTorch.

SENet is the winner of ImageNet-2017. The paper is not released yet.
"""

from __future__ import annotations

import torch
import torch.nn.functional as F
from torch import nn


class BasicBlock(nn.Module):
    def __init__(self, in_planes, planes, stride=1):
        super().__init__()
        self.conv1 = nn.Conv2d(
            in_planes,
            planes,
            kernel_size=3,
            stride=stride,
            padding=1,
            bias=False,
        )
        self.bn1 = nn.BatchNorm2d(planes)
        self.conv2 = nn.Conv2d(
            planes, planes, kernel_size=3, stride=1, padding=1, bias=False
        )
        self.bn2 = nn.BatchNorm2d(planes)

        self.shortcut = nn.Sequential()
        if stride != 1 or in_planes != planes:
            self.shortcut = nn.Sequential(
                nn.Conv2d(
                    in_planes, planes, kernel_size=1, stride=stride, bias=False
                ),
                nn.BatchNorm2d(planes),
            )

        # SE layers
        self.fc1 = nn.Conv2d(
            planes, planes // 16, kernel_size=1
        )  # Use nn.Conv2d instead of nn.Linear
        self.fc2 = nn.Conv2d(planes // 16, planes, kernel_size=1)

    def forward(self, x):
        out = F.relu(self.bn1(self.conv1(x)))
        out = self.bn2(self.conv2(out))

        # Squeeze
        w = F.avg_pool2d(out, out.size(2))
        w = F.relu(self.fc1(w))
        w = F.sigmoid(self.fc2(w))
        # Excitation
        out = out * w  # New broadcasting feature from v0.2!

        out += self.shortcut(x)
        out = F.relu(out)
        return out


class PreActBlock(nn.Module):
    def __init__(self, in_planes, planes, stride=1):
        super().__init__()
        self.bn1 = nn.BatchNorm2d(in_planes)
        self.nonlin1 = nn.ReLU(True)
        self.conv1 = nn.Conv2d(
            in_planes,
            planes,
            kernel_size=3,
            stride=stride,
            padding=1,
            bias=False,
        )
        self.bn2 = nn.BatchNorm2d(planes)
        self.nonlin2 = nn.ReLU(True)
        self.conv2 = nn.Conv2d(
            planes, planes, kernel_size=3, stride=1, padding=1, bias=False
        )

        if stride != 1 or in_planes != planes:
            self.shortcut = nn.Sequential(
                nn.Conv2d(
                    in_planes, planes, kernel_size=1, stride=stride, bias=False
                )
            )

        # SE layers
        self.fc1 = nn.Conv2d(planes, planes // 16, kernel_size=1)
        self.nonlin3 = nn.ReLU(True)
        self.fc2 = nn.Conv2d(planes // 16, planes, kernel_size=1)
        self.nonlin4 = nn.Sigmoid()

    def forward(self, x):
        out = self.nonlin1(self.bn1(x))
        shortcut = self.shortcut(out) if hasattr(self, "shortcut") else x
        out = self.conv1(out)
        out = self.conv2(self.nonlin2(self.bn2(out)))

        # Squeeze
        w = F.avg_pool2d(out, out.size(2))
        w = self.nonlin3(self.fc1(w))
        w = self.nonlin4(self.fc2(w))
        # Excitation
        out = out * w

        out += shortcut
        return out


class SENet(nn.Module):
    def __init__(self, block, num_blocks, num_classes=10, **kwargs):
        super().__init__()
        self.in_planes = 64

        self.conv1 = nn.Conv2d(
            3, 64, kernel_size=3, stride=1, padding=1, bias=False
        )
        self.bn1 = nn.BatchNorm2d(64)
        self.nonlin1 = nn.ReLU(True)
        self.layer1 = self._make_layer(block, 64, num_blocks[0], stride=1)
        self.layer2 = self._make_layer(block, 128, num_blocks[1], stride=2)
        self.layer3 = self._make_layer(block, 256, num_blocks[2], stride=2)
        self.layer4 = self._make_layer(block, 512, num_blocks[3], stride=2)
        self.linear = nn.Linear(512, num_classes)

    def _make_layer(self, block, planes, num_blocks, stride):
        strides = [stride] + [1] * (num_blocks - 1)
        layers = []
        for stride in strides:
            layers.append(block(self.in_planes, planes, stride))
            self.in_planes = planes
        return nn.Sequential(*layers)

    def forward(self, x):
        out = self.nonlin1(self.bn1(self.conv1(x)))
        out = self.layer1(out)
        out = self.layer2(out)
        out = self.layer3(out)
        out = self.layer4(out)
        out = F.avg_pool2d(out, 4)
        out = out.view(out.size(0), -1)
        out = self.linear(out)
        return out


def SENet18(**kwargs):
    return SENet(PreActBlock, [2, 2, 2, 2], **kwargs)


def test():
    net = SENet18()
    y = net(torch.randn(1, 3, 32, 32))
    print(y.size())
