import argparse
import os

import torch
import torch.nn as nn
import torch.nn.functional as F
import torch.optim as optim
from torchvision import datasets, transforms


# Pytorch model
class NeuralNet(nn.Module):
    def __init__(self, input_size, hidden_size, num_classes):
        super(NeuralNet, self).__init__()
        self.fc1 = nn.Linear(input_size, hidden_size)
        self.relu = nn.ReLU()
        self.fc2 = nn.Linear(hidden_size, num_classes)

    def forward(self, input1):
        out = self.fc1(input1)
        out = self.relu(out)
        out = self.fc2(out)
        return out


def my_loss(x, target, is_train=True):
    if is_train:
        return F.nll_loss(F.log_softmax(x, dim=1), target)
    else:
        return F.nll_loss(F.log_softmax(x, dim=1), target, reduction="sum")


# Helpers
def train(args, model, device, train_loader, optimizer, epoch):
    model.train()
    for batch_idx, (data, target) in enumerate(train_loader):
        if batch_idx == args.train_steps:
            break
        data, target = data.to(device), target.to(device)
        data = data.reshape(data.shape[0], -1)
        optimizer.zero_grad()
        output = model(data)
        loss = my_loss(output, target)
        loss.backward()
        optimizer.step()
        if batch_idx % args.log_interval == 0:
            print(
                "Train Epoch: {} [{}/{} ({:.0f}%)]\tLoss: {:.6f}".format(
                    epoch,
                    batch_idx * len(data),
                    len(train_loader.dataset),
                    100.0 * batch_idx / len(train_loader),
                    loss.item(),
                )
            )


def test(model, device, test_loader):
    model.eval()
    test_loss = 0
    correct = 0
    with torch.no_grad():
        for data, target in test_loader:
            data, target = data.to(device), target.to(device)
            data = data.reshape(data.shape[0], -1)
            output = model(data)
            # Stats
            test_loss += my_loss(output, target, False).item()
            pred = output.argmax(dim=1, keepdim=True)
            correct += pred.eq(target.view_as(pred)).sum().item()

    test_loss /= len(test_loader.dataset)

    print(
        "\nTest set: Average loss: {:.4f}, Accuracy: {}/{} ({:.0f}%)\n".format(
            test_loss, correct, len(test_loader.dataset), 100.0 * correct / len(test_loader.dataset)
        )
    )


def main():
    # Training settings
    parser = argparse.ArgumentParser(description="PyTorch MNIST Example")
    parser.add_argument(
        "--train-steps",
        type=int,
        default=-1,
        metavar="N",
        help="number of steps to train. Set -1 to run through whole dataset (default: -1)",
    )
    parser.add_argument(
        "--batch-size", type=int, default=20, metavar="N", help="input batch size for training (default: 20)"
    )
    parser.add_argument(
        "--test-batch-size", type=int, default=1000, metavar="N", help="input batch size for testing (default: 1000)"
    )
    parser.add_argument("--epochs", type=int, default=1, metavar="N", help="number of epochs to train (default: 1)")
    parser.add_argument("--lr", type=float, default=0.01, metavar="LR", help="learning rate (default: 0.01)")
    parser.add_argument("--no-cuda", action="store_true", default=False, help="disables CUDA training")
    parser.add_argument("--seed", type=int, default=1, metavar="S", help="random seed (default: 1)")
    parser.add_argument(
        "--log-interval",
        type=int,
        default=10,
        metavar="N",
        help="how many batches to wait before logging training status",
    )
    parser.add_argument("--save-path", type=str, default="", help="Path for Saving the current Model")

    # Basic setup
    args = parser.parse_args()
    if not args.no_cuda and torch.cuda.is_available():
        device = "cuda"
    else:
        device = "cpu"
    torch.manual_seed(args.seed)

    # Data loader
    train_loader = torch.utils.data.DataLoader(
        datasets.MNIST(
            "./data",
            train=True,
            download=True,
            transform=transforms.Compose([transforms.ToTensor(), transforms.Normalize((0.1307,), (0.3081,))]),
        ),
        batch_size=args.batch_size,
        shuffle=True,
    )

    if args.test_batch_size > 0:
        test_loader = torch.utils.data.DataLoader(
            datasets.MNIST(
                "./data",
                train=False,
                transform=transforms.Compose([transforms.ToTensor(), transforms.Normalize((0.1307,), (0.3081,))]),
            ),
            batch_size=args.test_batch_size,
            shuffle=True,
        )

    # Modeling
    model = NeuralNet(784, 500, 10).to(device)
    optimizer = optim.SGD(model.parameters(), lr=args.lr)

    # Train loop
    for epoch in range(1, args.epochs + 1):
        train(args, model, device, train_loader, optimizer, epoch)
        if args.test_batch_size > 0:
            test(model, device, test_loader)

    # Save model
    if args.save_path:
        torch.save(model.state_dict(), os.path.join(args.save_path, "mnist_cnn.pt"))


if __name__ == "__main__":
    main()