# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
import torch

from fairseq import utils
from fairseq.criterions import register_criterion
from fairseq.criterions.label_smoothed_cross_entropy import (
    LabelSmoothedCrossEntropyCriterion,
    LabelSmoothedCrossEntropyCriterionConfig,
    label_smoothed_nll_loss,
)


@register_criterion(
    "speech_text_pretrain_cross_entropy",
    dataclass=LabelSmoothedCrossEntropyCriterionConfig,
)
class SpeechTextPreTrainCrossEntCriterion(LabelSmoothedCrossEntropyCriterion):
    def __init__(self, task, sentence_avg, label_smoothing, report_accuracy=False):
        super().__init__(
            task, sentence_avg, label_smoothing, report_accuracy=report_accuracy
        )

    def forward(self, model, sample, reduce=True):
        net_output = model(**sample["net_input"])
        loss, nll_loss, nsentences, ntokens, n_correct = self.compute_loss(
            model, net_output, sample, reduce=reduce
        )
        sample_size = nsentences if self.sentence_avg else ntokens
        logging_output = {
            "loss": loss.data,
            "nll_loss": nll_loss.data,
            "ntokens": ntokens,
            "nsentences": nsentences,
            "sample_size": sample_size,
        }
        if self.report_accuracy:
            logging_output["n_correct"] = utils.item(n_correct)
            logging_output["total"] = utils.item(ntokens)
        return loss, sample_size, logging_output

    def get_lprobs_and_target(self, model, net_output, sample):
        lprobs = model.get_normalized_probs(net_output, log_probs=True)
        target = model.get_targets(sample, net_output)
        assert self.ignore_prefix_size == 0
        if self.ignore_prefix_size > 0:
            if getattr(lprobs, "batch_first", False):
                lprobs = lprobs[:, self.ignore_prefix_size :, :].contiguous()
                target = target[:, self.ignore_prefix_size :].contiguous()
            else:
                lprobs = lprobs[self.ignore_prefix_size :, :, :].contiguous()
                target = target[self.ignore_prefix_size :, :].contiguous()
        return lprobs, target

    def compute_loss(self, model, net_output, sample, reduce=True):
        lprobs, target = self.get_lprobs_and_target(model, net_output, sample)
        n_correct = 0
        if isinstance(target, dict):
            t_lprobs = target["target_logprobs"]

            if not lprobs.batch_first:
                lprobs = lprobs.transpose(0, 1)
                t_lprobs = t_lprobs.transpose(0, 1)
            nsentences, seq_len = lprobs.size()[:2]
            ntokens = nsentences * seq_len
            t_probs = t_lprobs.exp()
            mask_indices = (
                net_output[1]["mask_indices"][0]
                if len(net_output[1]["mask_indices"]) > 0
                else None
            )

            # mask_indices is True for those masking frames
            if mask_indices is not None:  # B X T
                t_probs = t_probs.masked_fill(mask_indices.eq(False).unsqueeze(-1), 0)
                ntokens = mask_indices.int().sum()
            t_probs = t_probs.detach()
            t_lprobs = t_lprobs.detach()
            loss = (
                -(t_probs * (lprobs - t_lprobs)).sum()
                if reduce
                else -(t_probs * (lprobs - t_lprobs)).sum(-1, keepdim=True)
            )
            nll_loss = loss
        else:
            nsentences = target.size(0)
            mask = target.ne(self.padding_idx)
            loss, nll_loss = label_smoothed_nll_loss(
                lprobs.view(-1, lprobs.size(-1)),
                target.view(-1),
                self.eps,
                ignore_index=self.padding_idx,
                reduce=reduce,
            )
            n_correct = torch.sum(
                lprobs.argmax(-1).masked_select(mask).eq(target.masked_select(mask))
            )
            ntokens = torch.sum(mask)
        return loss, nll_loss, nsentences, ntokens, n_correct