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


class LabelSmoothingCrossEntropy(nn.Module):
    def __init__(self, eps=0.1, reduction="mean"):
        super(LabelSmoothingCrossEntropy, self).__init__()
        self.eps = eps
        self.reduction = reduction

    def forward(self, output, target):
        c = output.size()[-1]
        log_preds = F.log_softmax(output, dim=-1)
        if self.reduction == "sum":
            loss = -log_preds.sum()
        else:
            loss = -log_preds.sum(dim=-1)
            if self.reduction == "mean":
                loss = loss.mean()
        return loss * self.eps / c + (1 - self.eps) * F.nll_loss(
            log_preds, target, reduction=self.reduction
        )
