import torch
import torch.nn.functional as F


def training_loop(model, optimizer, loss_function, train, validation, epochs=10):
    """A rudimentary PyTorch training loop for classification with training and validation data."""
    for epoch in range(epochs):
        # Switch to training mode.
        model.train()
        tloss = 0.0
        num_train = len(train)  # in batches
        for inp, target in train:  # batch loop (training)
            optimizer.zero_grad()
            output = model(inp)
            loss = loss_function(output, target)
            loss.backward()
            optimizer.step()
            tloss += loss.data.item()

        # Switch to inference mode.
        model.eval()
        vloss = 0.0
        num_validation = len(validation)  # in batches
        num_correct = 0
        num_total = 0
        for inp, target in validation:  # batch loop (validation)
            output = model(inp)
            loss = loss_function(output, target)
            vloss += loss.data.item()
            correct = torch.eq(torch.max(F.softmax(output), dim=1)[1], target).view(-1)
            num_correct += torch.sum(correct).item()
            num_total += correct.shape[0]

        # Report stats.
        print(
            "Epoch {:d}, Training loss = {:.2f} #{:d}, Validation loss = {:.2f} #{:d}, Accuracy = {:.2f} #{:d}".format(
                epoch,
                (tloss / num_train) if num_train != 0 else 0,
                num_train,
                (vloss / num_validation) if num_validation != 0 else 0,
                num_validation,
                (num_correct / num_total) if num_total != 0 else 0,
                num_total,
            )
        )