# Copyright (c) 2022, NVIDIA CORPORATION.  All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from typing import List

import torch
from torch import nn

from nemo.core.classes import Serialization, Typing, typecheck
from nemo.core.neural_types import LabelsType, LogitsType, LossType, MaskType, NeuralType

__all__ = ["BCEWithLogitsLoss"]


class BCEWithLogitsLoss(nn.BCEWithLogitsLoss, Serialization, Typing):
    """
    BCEWithLogitsLoss

    https://pytorch.org/docs/1.9.1/generated/torch.nn.BCEWithLogitsLoss.html
    """

    @property
    def input_types(self):
        """Returns definitions of module input ports.
        """
        return {
            "logits": NeuralType(["B"] + ["ANY"] * (self._logits_dim - 1), LogitsType()),
            "labels": [NeuralType(["B"] + ["ANY"] * (self._logits_dim - 2), LabelsType())],
            "loss_mask": NeuralType(["B"] + ["ANY"] * (self._logits_dim - 2), MaskType(), optional=True),
        }

    @property
    def output_types(self):
        """Returns definitions of module output ports.
        """
        return {"loss": NeuralType(elements_type=LossType())}

    def __init__(
        self,
        logits_ndim: int = 2,
        weight: torch.Tensor = None,
        reduction: str = "mean",
        pos_weight: torch.Tensor = None,
    ):
        """
        Args:
            logits_ndim: number of dimensions (or rank) of the logits tensor
            weight: list of rescaling weight given to each class
            reduction: type of the reduction over the batch
            pos_weight: weight given to positive samples
        """
        if pos_weight is not None and not torch.is_tensor(pos_weight):
            pos_weight = torch.FloatTensor(pos_weight)

        super().__init__(weight=weight, pos_weight=pos_weight, reduction=reduction)
        self._logits_dim = logits_ndim

    @typecheck()
    def forward(self, logits: float, labels: List[int], loss_mask: torch.Tensor = None):
        """
        Args:
            logits: output of the classifier
            labels: ground truth labels
        """
        labels = torch.stack(labels)
        labels = labels.t().float()

        return super().forward(logits, labels)