from __future__ import print_function
import torch
import torch.nn as nn
import torch.nn.functional as F
import torch.optim as optim
from torchvision import datasets, transforms
import numpy as np
import matplotlib.pyplot as plt

# 这里的epsilon先设定为几个值，到时候后面可视化展示它的影响如何
epsilons = [0, .05, .1, .15, .2, .25, .3]
# 这个预训练的模型需要提前下载，放在如下url的指定位置，下载链接如上
pretrained_model = "data/lenet_mnist_model.pth"
use_cuda=True

# 就是一个简单的模型结构
class Net(nn.Module):
    def __init__(self):
        super(Net, self).__init__()
        self.conv1 = nn.Conv2d(1, 10, kernel_size=5)
        self.conv2 = nn.Conv2d(10, 20, kernel_size=5)
        self.conv2_drop = nn.Dropout2d()
        self.fc1 = nn.Linear(320, 50)
        self.fc2 = nn.Linear(50, 10)

    def forward(self, x):
        x = F.relu(F.max_pool2d(self.conv1(x), 2))
        x = F.relu(F.max_pool2d(self.conv2_drop(self.conv2(x)), 2))
        x = x.view(-1, 320)
        x = F.relu(self.fc1(x))
        x = F.dropout(x, training=self.training)
        x = self.fc2(x)
        return F.log_softmax(x, dim=1)

# 运行需要稍等，这里表示下载并加载数据集
test_loader = torch.utils.data.DataLoader(
    datasets.MNIST('../data', train=False, download=True, transform=transforms.Compose([
            transforms.ToTensor(),
            ])),
        batch_size=1, shuffle=True)

# 看看我们有没有配置GPU，没有就是使用cpu
print("CUDA Available: ",torch.cuda.is_available())
device = torch.device("cuda" if (use_cuda and torch.cuda.is_available()) else "cpu")

# Initialize the network
model = Net().to(device)

# 加载前面的预训练模型
model.load_state_dict(torch.load(pretrained_model, map_location='cpu'))

# 设置为验证模式. 
model.eval()

# FGSM attack code
def fgsm_attack(image, epsilon, data_grad):
    # 使用sign（符号）函数，将对x求了偏导的梯度进行符号化
    sign_data_grad = data_grad.sign()
    # 通过epsilon生成对抗样本
    perturbed_image = image + epsilon*sign_data_grad
    # 做一个剪裁的工作，将torch.clamp内部大于1的数值变为1，小于0的数值等于0，防止image越界
    perturbed_image = torch.clamp(perturbed_image, 0, 1)
    # 返回对抗样本
    return perturbed_image

def test( model, device, test_loader, epsilon ):

    # 准确度计数器
    correct = 0
    # 对抗样本
    adv_examples = []

    # 循环所有测试集
    for data, target in test_loader:
        # Send the data and label to the device
        data, target = data.to(device), target.to(device)

        # Set requires_grad attribute of tensor. Important for Attack
        data.requires_grad = True

        # Forward pass the data through the model
        output = model(data)
        init_pred = output.max(1, keepdim=True)[1] # get the index of the max log-probability

        # If the initial prediction is wrong, dont bother attacking, just move on
        if init_pred.item() != target.item():
            continue

        # Calculate the loss
        loss = F.nll_loss(output, target)

        # Zero all existing gradients
        model.zero_grad()

        # Calculate gradients of model in backward pass
        loss.backward()

        # Collect datagrad
        data_grad = data.grad.data

        # Call FGSM Attack
        perturbed_data = fgsm_attack(data, epsilon, data_grad)

        # Re-classify the perturbed image
        output = model(perturbed_data)

        # Check for success
        final_pred = output.max(1, keepdim=True)[1] # get the index of the max log-probability
        if final_pred.item() == target.item():
            correct += 1
            # 这里都是为后面的可视化做准备
            if (epsilon == 0) and (len(adv_examples) < 5):
                adv_ex = perturbed_data.squeeze().detach().cpu().numpy()
                adv_examples.append( (init_pred.item(), final_pred.item(), adv_ex) )
        else:
            # 这里都是为后面的可视化做准备
            if len(adv_examples) < 5:
                adv_ex = perturbed_data.squeeze().detach().cpu().numpy()
                adv_examples.append( (init_pred.item(), final_pred.item(), adv_ex) )

    # Calculate final accuracy for this epsilon
    final_acc = correct/float(len(test_loader))
    print("Epsilon: {}\tTest Accuracy = {} / {} = {}".format(epsilon, correct, len(test_loader), final_acc))

    # Return the accuracy and an adversarial example
    return final_acc, adv_examples