# --------------------------------------------------------
# Pre-Training Transformer Decoder for End-to-End ASR Model with Unpaired Speech Data (https://arxiv.org/abs/2203.17113)
# Github source: https://github.com/microsoft/SpeechT5/tree/main/Speech2C
# Copyright (c) 2022 Microsoft
# Licensed under The MIT License [see LICENSE for details]
# Based on fairseq code bases
# https://github.com/pytorch/fairseq
# --------------------------------------------------------

import math
import re
from dataclasses import dataclass, field

import torch
import torch.nn.functional as F
from fairseq import metrics, utils
from fairseq.criterions import FairseqCriterion, register_criterion
from fairseq.criterions.label_smoothed_cross_entropy import label_smoothed_nll_loss
from fairseq.criterions.hubert_criterion import HubertCriterionConfig

@dataclass
class Speech2cCriterionConfig(HubertCriterionConfig):
    dec_weight: float = field(
        default=1.0,
        metadata={"help": "weights for decoder CE Loss, loss will be (hubert_loss + dec_weight * CE_Loss)"},
    )
    report_accuracy: bool = field(
        default=True,
        metadata={"help": "report decoder accuracy metric"},
    )
    ignore_prefix_size: int = field(
        default=0,
        metadata={"help": "Ignore first N tokens"},
    )
    label_smoothing: float = field(
        default=0.0,
        metadata={"help": "epsilon for label smoothing, 0 means no label smoothing"},
    )


@register_criterion("speech2c", dataclass=Speech2cCriterionConfig)
class Speech2cCriterion(FairseqCriterion):
    def __init__(self, task, pred_masked_weight, pred_nomask_weight, loss_weights=None, log_keys=None, dec_weight=1.0, report_accuracy=False, ignore_prefix_size=0, label_smoothing=0.0):
        super().__init__(task)
        self.pred_masked_weight = pred_masked_weight
        self.pred_nomask_weight = pred_nomask_weight
        self.loss_weights = loss_weights
        self.log_keys = [] if log_keys is None else log_keys
        self.dec_weight = dec_weight
        self.report_accuracy = report_accuracy
        self.ignore_prefix_size = ignore_prefix_size
        self.eps = label_smoothing
        self.padding_idx = task.dictionaries[0].pad()

    def forward(self, model, sample, reduce=True, log_pred=False):
        """Compute the loss for the given sample.
        Returns a tuple with three elements:
        1) the loss
        2) the sample size, which is used as the denominator for the gradient
        3) logging outputs to display while training
        """
        net_output = model(target_list=sample["target_list"], **sample["net_input"])
        loss = 0.0
        sample_size = 0
        logging_output = {}
        reduction = "sum" if reduce else "none"

        loss_m_list = []
        logp_m_list = model.get_logits(net_output, True)
        targ_m_list = model.get_targets(net_output, True)
        assert self.pred_masked_weight == 0 or len(logp_m_list) > 0
        for i, (logp_m, targ_m) in enumerate(zip(logp_m_list, targ_m_list)):
            loss_m = F.cross_entropy(logp_m, targ_m, reduction=reduction)
            loss_m_list.append(loss_m)
            logging_output[f"loss_m_{i}"] = loss_m.detach().item()
        if self.pred_masked_weight > 0:
            loss += self.pred_masked_weight * sum(loss_m_list)
            sample_size += targ_m_list[0].numel()

        loss_u_list = []
        logp_u_list = model.get_logits(net_output, False)
        targ_u_list = model.get_targets(net_output, False)
        assert self.pred_nomask_weight == 0 or len(logp_u_list) > 0
        for i, (logp_u, targ_u) in enumerate(zip(logp_u_list, targ_u_list)):
            loss_u = F.cross_entropy(logp_u, targ_u, reduction=reduction)
            loss_u_list.append(loss_u)
            logging_output[f"loss_u_{i}"] = loss_u.detach().item()
        if self.pred_nomask_weight > 0:
            loss += self.pred_nomask_weight * sum(loss_u_list)
            sample_size += targ_u_list[0].numel()

        if self.loss_weights is not None:
            assert hasattr(model, "get_extra_losses")
            extra_losses, names = model.get_extra_losses(net_output)
            if torch.is_tensor(extra_losses):
                extra_losses = [extra_losses]
                names = [names]
            if len(self.loss_weights) == 1 and len(extra_losses) != 1:
                self.loss_weights = [self.loss_weights[0]] * len(extra_losses)
            assert len(extra_losses) == len(
                self.loss_weights
            ), f"{len(extra_losses)}, {len(self.loss_weights)}"
            for p, n, coef in zip(extra_losses, names, self.loss_weights):
                if coef != 0 and p is not None:
                    p = coef * p.float() * sample_size
                    loss += p
                    logging_output[f"loss_{n}"] = p.item()

        if "decoder_target" in sample:
            dec_sample_size = sample["dec_ntokens"]
            dec_loss, dec_nll_loss = self.compute_ce_loss(model, net_output["decoder_out"], sample, reduce=reduce)
            loss = loss + (self.dec_weight * dec_loss *  sample_size / dec_sample_size)
            logging_output["dec_loss"] = dec_loss.item()
            logging_output["dec_nll_loss"] = dec_nll_loss.item()
            logging_output["dec_sample_size"] = dec_sample_size

            if self.report_accuracy:
                n_correct, total = self.compute_accuracy(model, net_output["decoder_out"], sample)
                logging_output["dec_n_correct"] = utils.item(n_correct.data)
                logging_output["total"] = utils.item(total.data)

        logging_output = {
            "loss": loss.item() if reduce else loss,
            "ntokens": sample_size,
            "nsentences": sample["id"].numel(),
            "sample_size": sample_size,
            **logging_output,
        }

        for lk in self.log_keys:
            if lk in net_output:
                logging_output[lk] = float((net_output[lk]))

        def compute_correct(logits):
            if logits.numel() == 0:
                return 0, 0
            else:
                assert logits.dim() > 1, logits.shape
                max = logits.argmax(-1) == 0
                min = logits.argmin(-1) == 0
                both = max & min
                corr = max.long().sum().item() - both.long().sum().item()
                count = max.numel()
                return corr, count

        with torch.no_grad():
            for i, logp_m in enumerate(logp_m_list):
                corr_m, count_m = compute_correct(logp_m)
                logging_output[f"correct_m_{i}"] = corr_m
                logging_output[f"count_m_{i}"] = count_m

            for i, logp_u in enumerate(logp_u_list):
                corr_u, count_u = compute_correct(logp_u)
                logging_output[f"correct_u_{i}"] = corr_u
                logging_output[f"count_u_{i}"] = count_u

        return loss, sample_size, logging_output

    def compute_ce_loss(self, model, net_output, sample, reduce=True):
        lprobs, target = self.get_lprobs_and_target(model, net_output, sample)
        loss, nll_loss = label_smoothed_nll_loss(
            lprobs,
            target,
            self.eps,
            ignore_index=self.padding_idx,
            reduce=reduce,
        )
        return loss, nll_loss

    def compute_accuracy(self, model, net_output, sample):
        lprobs, target = self.get_lprobs_and_target(model, net_output, sample)
        mask = target.ne(self.padding_idx)
        n_correct = torch.sum(
            lprobs.argmax(1).masked_select(mask).eq(target.masked_select(mask))
        )
        total = torch.sum(mask)
        return n_correct, total

    def get_lprobs_and_target(self, model, net_output, sample):
        lprobs = model.get_normalized_probs(net_output, log_probs=True)
        target = sample["decoder_target"]
        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.view(-1, lprobs.size(-1)), target.view(-1)

    @staticmethod
    def reduce_metrics(logging_outputs) -> None:
        """Aggregate logging outputs from data parallel training (copied from normal cross entropy)."""
        loss_sum = sum(log.get("loss", 0) for log in logging_outputs)
        ntokens = sum(log.get("ntokens", 0) for log in logging_outputs)
        sample_size = sum(log.get("sample_size", 0) for log in logging_outputs)

        metrics.log_scalar("loss", loss_sum / sample_size / math.log(2), sample_size, round=3)
        if sample_size != ntokens:
            metrics.log_scalar("nll_loss", loss_sum / ntokens / math.log(2), ntokens, round=3)
            metrics.log_derived("ppl", lambda meters: utils.get_perplexity(meters["nll_loss"].avg))
        else:
            metrics.log_derived("ppl", lambda meters: utils.get_perplexity(meters["loss"].avg))

        counts = {}
        for lk in logging_outputs[0].keys():
            if lk.startswith("count_"):
                val = sum(log[lk] for log in logging_outputs)
                metrics.log_scalar(lk, val)
                counts[lk] = val

        for lk in logging_outputs[0].keys():
            if lk.startswith("loss_"):
                val = sum(log[lk] for log in logging_outputs)
                metrics.log_scalar(lk, val / sample_size / math.log(2), round=3)
            elif lk.startswith("correct_"):
                val = sum(log[lk] for log in logging_outputs)
                metrics.log_scalar(lk, val / counts[re.sub("correct", "count", lk)])

        if "dec_loss" in logging_outputs[0]:
            dec_loss_sum = sum(log.get("dec_loss", 0) for log in logging_outputs)
            dec_nll_loss_sum = sum(log.get("dec_nll_loss", 0) for log in logging_outputs)
            dec_sample_size = sum(log.get("dec_sample_size", 0) for log in logging_outputs)
            metrics.log_scalar(
                "dec_loss", dec_loss_sum / dec_sample_size / math.log(2), dec_sample_size, round=3
            )
            metrics.log_scalar(
                "dec_nll_loss", dec_nll_loss_sum / dec_sample_size / math.log(2), dec_sample_size, round=3
            )
            metrics.log_derived(
                "dec_ppl", lambda meters: utils.get_perplexity(meters["dec_nll_loss"].avg)
            )
            total = utils.item(sum(log.get("total", 0) for log in logging_outputs))
            if total > 0:
                metrics.log_scalar("total", total)
                n_correct = utils.item(
                    sum(log.get("dec_n_correct", 0) for log in logging_outputs)
                )
                metrics.log_scalar("dec_n_correct", n_correct)
                metrics.log_derived(
                    "dec_accuracy",
                    lambda meters: round(
                        meters["dec_n_correct"].sum * 100.0 / meters["total"].sum, 3
                    )
                    if meters["total"].sum > 0
                    else float("nan"),
                )

    @staticmethod
    def aggregate_logging_outputs(logging_outputs):
        """Aggregate logging outputs from data parallel training."""
        raise NotImplementedError()

    @staticmethod
    def logging_outputs_can_be_summed() -> bool:
        """
        Whether the logging outputs returned by `forward` can be summed
        across workers prior to calling `reduce_metrics`. Setting this
        to True will improves distributed training speed.
        """
        return False