# 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 contextlib
import copy
import logging
import math
import re
from argparse import Namespace
from dataclasses import dataclass, field
from typing import Any, Optional

import numpy as np
import torch
import torch.nn as nn
import torch.nn.functional as F
from omegaconf import II, MISSING, open_dict

from fairseq import checkpoint_utils, tasks, utils
from fairseq.dataclass import FairseqDataclass
from fairseq.dataclass.utils import convert_namespace_to_omegaconf
from fairseq.models import (
    BaseFairseqModel,
    FairseqEncoder,
    FairseqEncoderDecoderModel,
    FairseqIncrementalDecoder,
    register_model,
)
from fairseq.models.wav2vec.wav2vec2 import MASKING_DISTRIBUTION_CHOICES, LAYER_TYPE_CHOICES, AdapterFast
from fairseq.modules import LayerNorm, PositionalEmbedding, TransformerDecoderLayer
from fairseq.tasks import FairseqTask

logger = logging.getLogger(__name__)


@dataclass
class Wav2Vec2AsrConfig(FairseqDataclass):
    w2v_path: str = field(
        default=MISSING, metadata={"help": "path to wav2vec 2.0 model"}
    )
    no_pretrained_weights: bool = field(
        default=False, metadata={"help": "if true, does not load pretrained weights"}
    )
    dropout_input: float = field(
        default=0.0,
        metadata={"help": "dropout to apply to the input (after feat extr)"},
    )

    final_dropout: float = field(
        default=0.0,
        metadata={"help": "dropout after transformer and before final projection"},
    )
    dropout: float = field(
        default=0.0, metadata={"help": "dropout probability inside wav2vec 2.0 model"}
    )
    attention_dropout: float = field(
        default=0.0,
        metadata={
            "help": "dropout probability for attention weights inside wav2vec 2.0 model"
        },
    )
    activation_dropout: float = field(
        default=0.0,
        metadata={
            "help": "dropout probability after activation in FFN inside wav2vec 2.0 model"
        },
    )

    # masking
    apply_mask: bool = field(
        default=False, metadata={"help": "apply masking during fine-tuning"}
    )
    mask_length: int = field(
        default=10, metadata={"help": "repeat the mask indices multiple times"}
    )
    mask_prob: float = field(
        default=0.5,
        metadata={
            "help": "probability of replacing a token with mask (normalized by length)"
        },
    )
    mask_selection: MASKING_DISTRIBUTION_CHOICES = field(
        default="static", metadata={"help": "how to choose masks"}
    )
    mask_other: float = field(
        default=0,
        metadata={
            "help": "secondary mask argument (used for more complex distributions), "
            "see help in compute_mask_indices"
        },
    )
    no_mask_overlap: bool = field(
        default=False, metadata={"help": "whether to allow masks to overlap"}
    )
    mask_min_space: Optional[int] = field(
        default=1,
        metadata={"help": "min space between spans (if no overlap is enabled)"},
    )
    require_same_masks: bool = field(
        default=True,
        metadata={
            "help": "whether to number of masked timesteps must be the same across all "
            "examples in a batch"
        },
    )
    mask_dropout: float = field(
        default=0.0,
        metadata={"help": "percent of masks to unmask for each sample"},
    )

    # channel masking
    mask_channel_length: int = field(
        default=10, metadata={"help": "length of the mask for features (channels)"}
    )
    mask_channel_prob: float = field(
        default=0.0, metadata={"help": "probability of replacing a feature with 0"}
    )
    mask_channel_selection: MASKING_DISTRIBUTION_CHOICES = field(
        default="static",
        metadata={"help": "how to choose mask length for channel masking"},
    )
    mask_channel_other: float = field(
        default=0,
        metadata={
            "help": "secondary mask argument (used for more complex distributions), "
            "see help in compute_mask_indicesh"
        },
    )
    no_mask_channel_overlap: bool = field(
        default=False, metadata={"help": "whether to allow channel masks to overlap"}
    )
    freeze_finetune_updates: int = field(
        default=0, metadata={"help": "dont finetune wav2vec for this many updates"}
    )
    feature_grad_mult: float = field(
        default=0.0, metadata={"help": "reset feature grad mult in wav2vec 2.0 to this"}
    )
    layerdrop: float = field(
        default=0.0, metadata={"help": "probability of dropping a layer in wav2vec 2.0"}
    )
    drop_path: float = 0
    mask_channel_min_space: Optional[int] = field(
        default=1,
        metadata={"help": "min space between spans (if no overlap is enabled)"},
    )
    mask_channel_before: bool = False
    normalize: bool = II("task.normalize")
    update_alibi: bool = True
    data: str = II("task.data")
    # this holds the loaded wav2vec args
    w2v_args: Any = None
    offload_activations: bool = field(
        default=False, metadata={"help": "offload_activations"}
    )
    min_params_to_wrap: int = field(
        default=int(1e8),
        metadata={
            "help": "minimum number of params for a layer to be wrapped with FSDP() when "
            "training with --ddp-backend=fully_sharded. Smaller values will "
            "improve memory efficiency, but may make torch.distributed "
            "communication less efficient due to smaller input sizes. This option "
            "is set to 0 (i.e., always wrap) when --checkpoint-activations or "
            "--offload-activations are passed."
        },
    )

    checkpoint_activations: bool = field(
        default=False,
        metadata={"help": "recompute activations and save memory for extra compute"},
    )
    ddp_backend: str = II("distributed_training.ddp_backend")

    zero_mask: bool = False
    load_ema: bool = False

    layer_decay: float = 1


    layer_type: LAYER_TYPE_CHOICES = field(
        default="transformer", metadata={"help": "layer type in encoder"}
    )
    # Adapter num
    adp_num: int = field(
        default=-1
    )
    adp_dim: int = field(
        default=64
    )
    adp_act_fn: str = field(
        default="relu"
    )
    adp_trf_idx: str = field(
        default="all",
    )

    freeze_regex: Optional[str] = field(
        default=None,
    )

@dataclass
class Wav2Vec2CtcConfig(Wav2Vec2AsrConfig):
    blank_weight: float = 0
    blank_mode: str = "add"


@register_model("wav2vec_ctc", dataclass=Wav2Vec2CtcConfig)
class Wav2VecCtc(BaseFairseqModel):
    def __init__(self, cfg: Wav2Vec2CtcConfig, w2v_encoder: BaseFairseqModel):
        super().__init__()
        self.cfg = cfg
        self.w2v_encoder = w2v_encoder
        self.blank_weight = cfg.blank_weight
        self.blank_mode = cfg.blank_mode

    def upgrade_state_dict_named(self, state_dict, name):
        super().upgrade_state_dict_named(state_dict, name)
        return state_dict

    @classmethod
    def build_model(cls, cfg: Wav2Vec2CtcConfig, task: FairseqTask):
        """Build a new model instance."""
        w2v_encoder = Wav2VecEncoder(cfg, len(task.target_dictionary))
        return cls(cfg, w2v_encoder)

    def get_logits(self, net_output, normalize=False):
        logits = net_output["encoder_out"]
        if self.blank_weight != 0:
            if self.blank_mode == "add":
                logits[..., 0] += self.blank_weight
            elif self.blank_mode == "set":
                logits[..., 0] = self.blank_weight
            else:
                raise Exception(f"invalid blank mode {self.blank_mode}")

        if net_output["padding_mask"] is not None and net_output["padding_mask"].any():
            number_of_classes = logits.size(-1)
            masking_tensor = torch.ones(
                number_of_classes, device=logits.device
            ) * float("-inf")
            masking_tensor[0] = 0

            if logits.size(0) > net_output["padding_mask"].size(1):
                net_output["padding_mask"] = F.pad(
                    net_output["padding_mask"], (1, 0), value=False
                )

            logits[net_output["padding_mask"].T] = masking_tensor.type_as(logits)

        if normalize:
            logits = utils.log_softmax(logits.float(), dim=-1)

        return logits

    def get_normalized_probs(self, net_output, log_probs):
        """Get normalized probabilities (or log probs) from a net's output."""

        logits = self.get_logits(net_output)

        if log_probs:
            return utils.log_softmax(logits.float(), dim=-1)
        else:
            return utils.softmax(logits.float(), dim=-1)

    def forward(self, **kwargs):
        x = self.w2v_encoder(**kwargs)
        return x


@dataclass
class Wav2Vec2Seq2SeqConfig(Wav2Vec2AsrConfig):
    decoder_embed_dim: int = field(
        default=768, metadata={"help": "decoder embedding dimension"}
    )
    decoder_ffn_embed_dim: int = field(
        default=3072, metadata={"help": "decoder embedding dimension for FFN"}
    )
    decoder_layers: int = field(default=6, metadata={"help": "num of decoder layers"})
    decoder_layerdrop: float = field(
        default=0.0, metadata={"help": "decoder layerdrop chance"}
    )
    decoder_attention_heads: int = field(
        default=4, metadata={"help": "num decoder attention heads"}
    )
    decoder_learned_pos: bool = field(
        default=False,
        metadata={"help": "use learned positional embeddings in the decoder"},
    )
    decoder_normalize_before: bool = field(
        default=False, metadata={"help": "apply layernorm before each decoder block"}
    )
    no_token_positional_embeddings: bool = field(
        default=False,
        metadata={
            "help": "if set, disables positional embeddings (outside self attention)"
        },
    )
    decoder_dropout: float = field(
        default=0.0, metadata={"help": "dropout probability in the decoder"}
    )
    decoder_attention_dropout: float = field(
        default=0.0,
        metadata={
            "help": "dropout probability for attention weights inside the decoder"
        },
    )
    decoder_activation_dropout: float = field(
        default=0.0,
        metadata={
            "help": "dropout probability after activation in FFN inside the decoder"
        },
    )
    max_target_positions: int = field(
        default=2048, metadata={"help": "max target positions"}
    )
    share_decoder_input_output_embed: bool = field(
        default=False, metadata={"help": "share decoder input and output embeddings"}
    )
    autoregressive: bool = II("task.autoregressive")


@register_model("wav2vec_seq2seq", dataclass=Wav2Vec2Seq2SeqConfig)
class Wav2Vec2Seq2SeqModel(FairseqEncoderDecoderModel):
    def __init__(self, encoder, decoder):
        super().__init__(encoder, decoder)

    @classmethod
    def build_model(cls, cfg: Wav2Vec2Seq2SeqConfig, task: FairseqTask):
        """Build a new model instance."""

        assert (
            cfg.autoregressive
        ), "Please set task.autoregressive=true for seq2seq asr models"

        src_dict, tgt_dict = task.source_dictionary, task.target_dictionary

        def build_embedding(dictionary, embed_dim):
            num_embeddings = len(dictionary)
            padding_idx = dictionary.pad()
            emb = Embedding(num_embeddings, embed_dim, padding_idx)
            return emb

        decoder_embed_tokens = build_embedding(tgt_dict, cfg.decoder_embed_dim)

        encoder = cls.build_encoder(cfg)
        decoder = cls.build_decoder(cfg, tgt_dict, decoder_embed_tokens)

        return Wav2Vec2Seq2SeqModel(encoder, decoder)

    @classmethod
    def build_encoder(cls, cfg: Wav2Vec2AsrConfig):
        return Wav2VecEncoder(cfg)

    @classmethod
    def build_decoder(cls, cfg: Wav2Vec2Seq2SeqConfig, tgt_dict, embed_tokens):
        return TransformerDecoder(cfg, tgt_dict, embed_tokens)

    def forward(self, **kwargs):
        encoder_out = self.encoder(**kwargs)
        decoder_out = self.decoder(encoder_out=encoder_out, **kwargs)
        return decoder_out

    def upgrade_state_dict_named(self, state_dict, name):
        super().upgrade_state_dict_named(state_dict, name)
        return state_dict


class Wav2VecEncoder(FairseqEncoder):
    def __init__(self, cfg: Wav2Vec2AsrConfig, output_size=None):
        self.apply_mask = cfg.apply_mask

        arg_overrides = {
            "dropout": cfg.dropout,
            "activation_dropout": cfg.activation_dropout,
            "dropout_input": cfg.dropout_input,
            "attention_dropout": cfg.attention_dropout,
            "mask_length": cfg.mask_length,
            "mask_prob": cfg.mask_prob,
            "require_same_masks": getattr(cfg, "require_same_masks", True),
            "pct_holes": getattr(cfg, "mask_dropout", 0),
            "mask_selection": cfg.mask_selection,
            "mask_other": cfg.mask_other,
            "no_mask_overlap": cfg.no_mask_overlap,
            "mask_channel_length": cfg.mask_channel_length,
            "mask_channel_prob": cfg.mask_channel_prob,
            "mask_channel_before": cfg.mask_channel_before,
            "mask_channel_selection": cfg.mask_channel_selection,
            "mask_channel_other": cfg.mask_channel_other,
            "no_mask_channel_overlap": cfg.no_mask_channel_overlap,
            "encoder_layerdrop": cfg.layerdrop,
            "feature_grad_mult": cfg.feature_grad_mult,
            "checkpoint_activations": cfg.checkpoint_activations,
            "offload_activations": cfg.offload_activations,
            "min_params_to_wrap": cfg.min_params_to_wrap,
            # d2v multi args
            "encoder_dropout": cfg.dropout,
            "drop_path": getattr(cfg, "drop_path", 0),
            "mask_dropout": getattr(cfg, "mask_dropout", 0),
            "zero_mask": getattr(cfg, "zero_mask", False),
            "local_grad_mult": cfg.feature_grad_mult,
            "layerdrop": cfg.layerdrop,
            "prenet_layerdrop": cfg.layerdrop,
            "prenet_dropout": cfg.dropout,
            "post_mlp_drop": cfg.dropout,
            "encoder_zero_mask": getattr(cfg, "zero_mask", False),
            "inverse_mask": False,
            "learned_alibi_scale": getattr(cfg, "update_alibi", True),
        }

        if cfg.w2v_args is None:
            state = checkpoint_utils.load_checkpoint_to_cpu(cfg.w2v_path, arg_overrides)
            w2v_args = state.get("cfg", None)
            if w2v_args is None:
                w2v_args = convert_namespace_to_omegaconf(state["args"])
            w2v_args.criterion = None
            w2v_args.lr_scheduler = None

            cfg.w2v_args = w2v_args

            logger.info(w2v_args)

        else:
            state = None
            w2v_args = cfg.w2v_args
            if isinstance(w2v_args, Namespace):
                cfg.w2v_args = w2v_args = convert_namespace_to_omegaconf(w2v_args)

        self.is_d2v_multi = "data2vec_multi" in w2v_args.model.get("_name", None)

        if not self.is_d2v_multi:
            model_normalized = w2v_args.task.get(
                "normalize", w2v_args.model.get("normalize", False)
            )
            assert cfg.normalize == model_normalized, (
                "Fine-tuning works best when data normalization is the same. "
                "Please check that --normalize is set or unset for both pre-training and here"
            )

            with open_dict(w2v_args):
                args_replacement = ["checkpoint_activations", "layer_type", 
                    "adp_num", "adp_dim",
                    "adp_act_fn", "adp_trf_idx"]
                for _args in args_replacement:
                    if hasattr(cfg, _args) and getattr(cfg, _args, None) is not None:
                        w2v_args.model[_args] = getattr(cfg, _args, None)

            if hasattr(cfg, "checkpoint_activations") and cfg.checkpoint_activations:
                with open_dict(w2v_args):
                    w2v_args.model.checkpoint_activations = cfg.checkpoint_activations

            w2v_args.task.data = cfg.data
            task = tasks.setup_task(w2v_args.task, from_checkpoint=True)
            model = task.build_model(w2v_args.model, from_checkpoint=True)
            model.remove_pretraining_modules()
            d = w2v_args.model.encoder_embed_dim
        else:
            assert cfg.normalize

            if hasattr(w2v_args.task, "audio"):
                w2v_args.task.audio.data = cfg.data
            else:
                w2v_args.task.data = cfg.data
            task = tasks.setup_task(w2v_args.task, from_checkpoint=True)

            model = task.build_model(w2v_args.model, from_checkpoint=True)

            model.remove_pretraining_modules(modality="audio")
            d = w2v_args.model.embed_dim

        if state is not None and not cfg.no_pretrained_weights:
            if cfg.load_ema:
                assert "_ema" in state["model"]
                for k in state["model"]["_ema"]:
                    mk = "encoder." + k
                    assert mk in state["model"], mk
                    state["model"][mk] = state["model"]["_ema"][k]
            self.load_model_weights(state, model, cfg)

        super().__init__(task.source_dictionary)

        self.w2v_model = model

        self.final_dropout = nn.Dropout(cfg.final_dropout)
        self.freeze_finetune_updates = cfg.freeze_finetune_updates
        self.num_updates = 0

        targ_d = None
        self.proj = None

        if output_size is not None:
            targ_d = output_size
        elif getattr(cfg, "decoder_embed_dim", d) != d:
            targ_d = cfg.decoder_embed_dim

        if targ_d is not None:
            self.proj = Linear(d, targ_d)

        if cfg.freeze_regex is not None:
            self.freeze_regex(cfg.freeze_regex)

        layer_decay = getattr(cfg, "layer_decay", 1)
        if layer_decay < 1:
            mod_encs = list(model.modality_encoders.values())
            assert len(mod_encs) == 1, len(mod_encs)
            blocks = list(mod_encs[0].context_encoder.blocks) + list(model.blocks)
            num_layers = len(blocks) + 1
            layer_scales = list(
                layer_decay ** (num_layers - i) for i in range(num_layers + 1)
            )

            for i, b in enumerate(blocks):
                lid = i + 1
                if layer_scales[lid] == 1.0:
                    continue

                for n, p in b.named_parameters():
                    optim_override = getattr(p, "optim_overrides", {})
                    if "optimizer" not in optim_override:
                        optim_override["optimizer"] = {}

                    optim_override["optimizer"]["lr_scale"] = layer_scales[lid]
                    p.optim_overrides = optim_override

    def freeze_regex(self, pattern):
        unfrozen_names = []
        for name, param in self.named_parameters():
            if re.fullmatch(pattern, name) is not None:
                param.requires_grad_(False)
            else:
                unfrozen_names.append(name)

    def load_model_weights(self, state, model, cfg):
        if cfg.ddp_backend == "fully_sharded":
            from fairseq.distributed import FullyShardedDataParallel

            for name, module in model.named_modules():
                if "encoder.layers" in name and len(name.split(".")) == 3:
                    # Only for layers, we do a special handling and load the weights one by one
                    # We dont load all weights together as that wont be memory efficient and may
                    # cause oom
                    new_dict = {
                        k.replace(name + ".", ""): v
                        for (k, v) in state["model"].items()
                        if name + "." in k
                    }
                    assert isinstance(module, FullyShardedDataParallel)
                    with module.summon_full_params():
                        module.load_state_dict(new_dict, strict=True)
                    module._reset_lazy_init()

            # Once layers are loaded, filter them out and load everything else.
            r = re.compile("encoder.layers.\d.")
            filtered_list = list(filter(r.match, state["model"].keys()))

            new_big_dict = {
                k: v for (k, v) in state["model"].items() if k not in filtered_list
            }

            model.load_state_dict(new_big_dict, strict=False)
        else:
            to_delete = {"_ema", "target_proj", "decoder"}
            for k in to_delete:
                if k in state["model"]:
                    del state["model"][k]

            if hasattr(model, "modality_encoders"):
                if "modality_encoders.AUDIO.encoder_mask" not in state["model"]:
                    model.modality_encoders["AUDIO"].encoder_mask = None
                elif not cfg.zero_mask:
                    model.modality_encoders["AUDIO"].encoder_mask = None
                    del state["model"]["modality_encoders.AUDIO.encoder_mask"]

                for k in list(state["model"].keys()):
                    if k.startswith("modality_encoders.") and not k.startswith(
                        "modality_encoders.AUDIO"
                    ):
                        del state["model"][k]

            print(model)
            model.load_state_dict(state["model"], strict=True)

    def set_num_updates(self, num_updates):
        """Set the number of parameters updates."""
        super().set_num_updates(num_updates)
        self.num_updates = num_updates

    def forward(self, source, padding_mask, **kwargs):

        w2v_args = {
            "source": source,
            "padding_mask": padding_mask,
            "mask": self.apply_mask and self.training,
        }
        if "corpus_key" in kwargs:
            w2v_args["corpus_key"] = kwargs["corpus_key"]

        if self.is_d2v_multi:
            w2v_args["mode"] = "AUDIO"

        ft = self.freeze_finetune_updates <= self.num_updates

        with torch.no_grad() if not ft else contextlib.ExitStack():
            res = self.w2v_model.extract_features(**w2v_args)

            x = res["x"]
            padding_mask = res["padding_mask"]

            # B x T x C -> T x B x C
            x = x.transpose(0, 1)

        x = self.final_dropout(x)

        if self.proj:
            x = self.proj(x)

        return {
            "encoder_out": x,  # T x B x C
            "padding_mask": padding_mask,  # B x T,
            "layer_results": res["layer_results"],
        }

    def forward_torchscript(self, net_input):
        if torch.jit.is_scripting():
            return self.forward(net_input["source"], net_input["padding_mask"])
        else:
            return self.forward_non_torchscript(net_input)

    def reorder_encoder_out(self, encoder_out, new_order):
        if encoder_out["encoder_out"] is not None:
            encoder_out["encoder_out"] = encoder_out["encoder_out"].index_select(
                1, new_order
            )
        if encoder_out["padding_mask"] is not None:
            encoder_out["padding_mask"] = encoder_out["padding_mask"].index_select(
                0, new_order
            )
        return encoder_out

    def max_positions(self):
        """Maximum input length supported by the encoder."""
        return None

    def upgrade_state_dict_named(self, state_dict, name):
        return state_dict


class TransformerDecoder(FairseqIncrementalDecoder):
    """
    Transformer decoder consisting of *args.decoder_layers* layers. Each layer
    is a :class:`TransformerDecoderLayer`.

    Args:
        args (argparse.Namespace): parsed command-line arguments
        dictionary (~fairseq.data.Dictionary): decoding dictionary
        embed_tokens (torch.nn.Embedding): output embedding
        no_encoder_attn (bool, optional): whether to attend to encoder outputs
            (default: False).
    """

    def __init__(
        self,
        cfg: Wav2Vec2Seq2SeqConfig,
        dictionary,
        embed_tokens,
        no_encoder_attn=False,
    ):
        super().__init__(dictionary)

        self.dropout = cfg.decoder_dropout
        self.share_input_output_embed = cfg.share_decoder_input_output_embed

        input_embed_dim = embed_tokens.embedding_dim
        embed_dim = cfg.decoder_embed_dim
        self.output_embed_dim = cfg.decoder_embed_dim

        self.layerdrop = cfg.decoder_layerdrop

        self.padding_idx = embed_tokens.padding_idx
        self.max_target_positions = cfg.max_target_positions

        self.embed_tokens = embed_tokens
        self.embed_scale = math.sqrt(embed_dim)  # todo: try with input_embed_dim

        self.project_in_dim = (
            Linear(input_embed_dim, embed_dim, bias=False)
            if embed_dim != input_embed_dim
            else None
        )

        self.embed_positions = (
            PositionalEmbedding(
                cfg.max_target_positions,
                embed_dim,
                self.padding_idx,
                learned=cfg.decoder_learned_pos,
            )
            if not cfg.no_token_positional_embeddings
            else None
        )

        # TODO: update this when transformer gets converted to dataclass configs
        transformer_cfg = copy.deepcopy(cfg)
        with open_dict(transformer_cfg):
            transformer_cfg.dropout = transformer_cfg.decoder_dropout
            transformer_cfg.attention_dropout = (
                transformer_cfg.decoder_attention_dropout
            )
            transformer_cfg.activation_dropout = (
                transformer_cfg.decoder_activation_dropout
            )

        self.layers = nn.ModuleList([])
        self.layers.extend(
            [
                TransformerDecoderLayer(transformer_cfg, no_encoder_attn)
                for _ in range(transformer_cfg.decoder_layers)
            ]
        )

        if not self.share_input_output_embed:
            self.embed_out = nn.Parameter(
                torch.Tensor(len(dictionary), self.output_embed_dim)
            )
            nn.init.normal_(self.embed_out, mean=0, std=self.output_embed_dim**-0.5)

        if transformer_cfg.decoder_normalize_before:
            self.layer_norm = LayerNorm(embed_dim)
        else:
            self.layer_norm = None

    def forward(
        self, prev_output_tokens, encoder_out=None, incremental_state=None, **unused
    ):
        """
        Args:
            prev_output_tokens (LongTensor): previous decoder outputs of shape
                `(batch, tgt_len)`, for teacher forcing
            encoder_out (Tensor, optional): output from the encoder, used for
                encoder-side attention
            incremental_state (dict): dictionary used for storing state during
                :ref:`Incremental decoding`

        Returns:
            tuple:
                - the decoder's output of shape `(batch, tgt_len, vocab)`
                - a dictionary with any model-specific outputs
        """

        if type(prev_output_tokens) == list:
            max_len = max((len(x) for x in prev_output_tokens))
            tmp = torch.zeros(
                [len(prev_output_tokens), max_len], device=prev_output_tokens[0].device
            )
            for (i, p) in enumerate(prev_output_tokens):
                tmp[i, : len(p)] = p
            prev_output_tokens = tmp

        prev_output_tokens = prev_output_tokens.long()
        x, extra = self.extract_features(
            prev_output_tokens, encoder_out, incremental_state
        )
        x = self.output_layer(x)
        return x, extra

    def extract_features(
        self, prev_output_tokens, encoder_out=None, incremental_state=None, **unused
    ):
        """
        Similar to *forward* but only return features.

        Returns:
            tuple:
                - the decoder's features of shape `(batch, tgt_len, embed_dim)`
                - a dictionary with any model-specific outputs
        """

        # embed positions
        positions = (
            self.embed_positions(
                prev_output_tokens, incremental_state=incremental_state
            )
            if self.embed_positions is not None
            else None
        )

        if incremental_state is not None:
            prev_output_tokens = prev_output_tokens[:, -1:]
            if positions is not None:
                positions = positions[:, -1:]

        # embed tokens and positions
        x = self.embed_scale * self.embed_tokens(prev_output_tokens)

        if self.project_in_dim is not None:
            x = self.project_in_dim(x)

        if positions is not None:
            x += positions
        x = F.dropout(x, p=self.dropout, training=self.training)

        # B x T x C -> T x B x C
        x = x.transpose(0, 1)
        attn = None

        inner_states = [x]

        # decoder layers
        self_attn_padding_mask = None
        if prev_output_tokens.eq(self.padding_idx).any():
            self_attn_padding_mask = prev_output_tokens.eq(self.padding_idx)
        for layer in self.layers:
            dropout_probability = np.random.random()
            if not self.training or (dropout_probability > self.layerdrop):
                x, attn, _ = layer(
                    x,
                    encoder_out["encoder_out"] if encoder_out is not None else None,
                    encoder_out["padding_mask"] if encoder_out is not None else None,
                    incremental_state,
                    self_attn_mask=self.buffered_future_mask(x)
                    if incremental_state is None
                    else None,
                    self_attn_padding_mask=self_attn_padding_mask,
                )
                inner_states.append(x)

        if self.layer_norm:
            x = self.layer_norm(x)

        # T x B x C -> B x T x C
        x = x.transpose(0, 1)

        return x, {"attn": attn, "inner_states": inner_states}

    def output_layer(self, features, **kwargs):
        """Project features to the vocabulary size."""
        # project back to size of vocabulary
        if self.share_input_output_embed:
            return F.linear(features, self.embed_tokens.weight)
        else:
            return F.linear(features, self.embed_out)

    def max_positions(self):
        """Maximum output length supported by the decoder."""
        if self.embed_positions is None:
            return self.max_target_positions
        return min(self.max_target_positions, self.embed_positions.max_positions)

    def buffered_future_mask(self, tensor):
        dim = tensor.size(0)
        if (
            not hasattr(self, "_future_mask")
            or self._future_mask is None
            or self._future_mask.device != tensor.device
            or self._future_mask.size(0) < dim
        ):
            self._future_mask = torch.triu(
                utils.fill_with_neg_inf(tensor.new(dim, dim)), 1
            )
        return self._future_mask[:dim, :dim]

    def upgrade_state_dict_named(self, state_dict, name):
        return state_dict


def Embedding(num_embeddings, embedding_dim, padding_idx):
    m = nn.Embedding(num_embeddings, embedding_dim, padding_idx=padding_idx)
    nn.init.normal_(m.weight, mean=0, std=embedding_dim**-0.5)
    nn.init.constant_(m.weight[padding_idx], 0)
    return m


def Linear(in_features, out_features, bias=True):
    m = nn.Linear(in_features, out_features, bias)
    nn.init.xavier_uniform_(m.weight)
    if bias:
        nn.init.constant_(m.bias, 0.0)
    return m
