import torch
import torch.nn as nn
from torch.utils.model_zoo import load_url as load_state_dict_from_url
from typing import Any


__all__ = ['AlexNet', 'alexnet']


model_urls = {
    'alexnet': 'https://download.pytorch.org/models/alexnet-owt-4df8aa71.pth',
}


class AlexNet(nn.Module):
    '''
    AlexNet modified (features) for CIFAR10. Source: https://github.com/icpm/pytorch-cifar10/blob/master/models/AlexNet.py. 
    '''
    def __init__(self, num_classes: int = 1000) -> None:
        super(AlexNet, self).__init__()
        self.features = nn.Sequential(
            nn.Conv2d(3, 64, kernel_size=3, stride=2, padding=1),
            nn.ReLU(inplace=True),
            nn.MaxPool2d(kernel_size=2),
            nn.Conv2d(64, 192, kernel_size=3, padding=1),
            nn.ReLU(inplace=True),
            nn.MaxPool2d(kernel_size=2),
            nn.Conv2d(192, 384, kernel_size=3, padding=1),
            nn.ReLU(inplace=True),
            nn.Conv2d(384, 256, kernel_size=3, padding=1),
            nn.ReLU(inplace=True),
            nn.Conv2d(256, 256, kernel_size=3, padding=1),
            nn.ReLU(inplace=True),
            nn.MaxPool2d(kernel_size=2),
        )
        # self.avgpool = nn.AdaptiveAvgPool2d((6, 6))
        self.fc_block = nn.Sequential(
            nn.Linear(256 * 2 * 2, 4096, bias=False),
            nn.BatchNorm1d(4096),
            nn.ReLU(inplace=True),
            nn.Linear(4096, 4096, bias=False),
            nn.BatchNorm1d(4096),
            nn.ReLU(inplace=True),
        )
        self.classifier = nn.Sequential(
            nn.Linear(4096, num_classes),
        )
        self.penultimate_active = False

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        x = self.features(x)
        # x = self.avgpool(x)
        x = torch.flatten(x, 1)
        z = self.fc_block(x)
        x = self.classifier(z)
        if self.penultimate_active:
            return z, x
        return x


def alexnet(pretrained: bool = False, progress: bool = True, **kwargs: Any) -> AlexNet:
    r"""AlexNet model architecture from the
    `"One weird trick..." <https://arxiv.org/abs/1404.5997>`_ paper.
    Args:
        pretrained (bool): If True, returns a model pre-trained on ImageNet
        progress (bool): If True, displays a progress bar of the download to stderr
    """
    model = AlexNet(**kwargs)
    if pretrained:
        state_dict = load_state_dict_from_url(model_urls['alexnet'],
                                              progress=progress)
        model.load_state_dict(state_dict)
    return model