model.py

from transformers import PreTrainedModel, PretrainedConfig, Wav2Vec2ForCTC
import json
import torch
from torch import nn
from torch.nn.utils.rnn import pad_sequence
import math
from typing import Optional

# x: torch.FloatTensor [T, B, D]
# mask: torch.BoolTensor [B, T], where True indicates padding
# returns: torch.LongTensor [B]
def get_lengths(x, mask=None):
    if mask is not None:
        return (~mask).long().sum(dim=1)
    else:
        return torch.LongTensor([x.size(0)] * x.size(1)).to(x.device)

# lens: torch.LongTensor [B]
# returns: torch.BoolTensor [B, max_lens], where True indicates padding
def lengths_to_padding_mask(lens):
    bsz, max_lens = lens.size(0), torch.max(lens).item()
    mask = torch.arange(max_lens).to(lens.device).view(1, max_lens)
    mask = mask.expand(bsz, -1) >= lens.view(bsz, 1).expand(-1, max_lens)
    return mask

# input_lengths: torch.LongTensor [B]
def get_output_lengths(input_lengths):
    conv_feature_layers = "[(512, 10, 5)] + [(512, 3, 2)] * 4 + [(512,2,2)] + [(512,2,2)]"
    conv_cfg_list = eval(conv_feature_layers)

    def _conv_out_length(input_length, kernel_size, stride):
        return torch.floor((input_length - kernel_size) / stride + 1)

    for i in range(len(conv_cfg_list)):
        input_lengths = _conv_out_length(
            input_lengths, conv_cfg_list[i][1], conv_cfg_list[i][2]
        )

    return input_lengths.to(torch.long)

class ZeroSwotEncoderConfig(PretrainedConfig):
    model_type = "zero_swot_encoder"
    def __init__(
        self,
        wav2vec2_model_name_or_path="",
        compression_adapter=None,
        embed_dim=1024,
        **kwargs
    ):
        super().__init__(**kwargs)
        self.wav2vec2_model_name_or_path = wav2vec2_model_name_or_path
        self.compression_adapter = compression_adapter
        self.embed_dim = embed_dim

    @classmethod
    def from_json_file(cls, json_file):
        with open(json_file, "r") as reader:
            text = reader.read()
        config_dict = json.loads(text)
        return cls(**config_dict)

class ZeroSwotEncoderModel(PreTrainedModel):
    config_class = ZeroSwotEncoderConfig
    model_type = "zero_swot_encoder"

    def __init__(self, config):
        super().__init__(config)

        self.wav2vec2 = Wav2Vec2ForCTC.from_pretrained(config.wav2vec2_model_name_or_path)
        self.compression_adapter = CompressionAdapter(config.compression_adapter)
        self.speech_embedder = SpeechEmbedder(config.embed_dim)

    def forward(self, input_values, attention_mask=None):
        input_lens = get_lengths(input_values, ~attention_mask)

        # Forward pass through wav2vec2 encoder
        x = self.wav2vec2.wav2vec2(input_values, attention_mask)[0]  # [B, T, D]
        # CTC predictions
        preds = self.wav2vec2.lm_head(x).argmax(-1)  # [B, T]
        # Get output lengths for x
        output_lens = get_output_lengths(input_lens)

        # Compression
        x, mask, _ = self.compression_adapter(x, preds, output_lens) # [B, N, D] with N << T

        # BOS and EOS embeddings
        x, mask = self.speech_embedder(x, mask) # [B, N+2, D]

        return x, mask     


class SpeechEmbedder(nn.Module):
    def __init__(self, embed_dim):
        super().__init__()

        self.embed_dim = embed_dim
        self.bos_emb = nn.Parameter(torch.empty(embed_dim))
        self.eos_emb = nn.Parameter(torch.empty(embed_dim))

        self.scale = self.embed_dim ** 0.5
        
    def forward(self, x, padding_mask=None):
        """Add special embedding and positional embedding.
        Args:
            x (FloatTensor): (B, T, C)
            padding_mask (ByteTensor): (B, T)
        Outputs:
            x (FloatTensor): (B, T+2, C)
            padding_mask (ByteTensor): (B, T+2)
        """
        B = x.size(0)
        lengths = get_lengths(x.transpose(0, 1), padding_mask)
        assert B == len(lengths)
        
        if padding_mask is not None:
            x = x * (1 - padding_mask.unsqueeze(-1).type_as(x))
                
        # prepend bos
        x = torch.cat([self.bos_emb.view(1, 1, -1).expand(B, 1, -1), x], dim=1)
        lengths += 1
        
        # append padding (zeros) and then convert first padding to eos
        x = torch.cat([x, torch.zeros(B, 1, x.size(-1), device=x.device, dtype=x.dtype)], dim=1)
        for i in range(B):
            x[i, lengths[i], :] = self.eos_emb
        lengths += 1
        
        padding_mask = lengths_to_padding_mask(lengths)

        x = x * self.scale
            
        return x, padding_mask


class PositionalEmbedding(nn.Module):
    def __init__(self, num_embeddings, embedding_dim, padding_idx):
        super().__init__()
        self.embedding_dim = embedding_dim
        self.padding_idx = padding_idx if padding_idx is not None else 0
        num_embeddings += padding_idx + 1
        self.weights = PositionalEmbedding.get_embedding(
            num_embeddings, embedding_dim, padding_idx
        )
        self.register_buffer("_float_tensor", torch.FloatTensor(1))
        self.max_positions = int(1e5)

    @staticmethod
    def get_embedding(
        num_embeddings: int, embedding_dim: int, padding_idx: Optional[int] = None
    ):
        half_dim = embedding_dim // 2
        emb = math.log(10000) / (half_dim - 1)
        emb = torch.exp(torch.arange(half_dim, dtype=torch.float) * -emb)
        emb = torch.arange(num_embeddings, dtype=torch.float).unsqueeze(1) * emb.unsqueeze(0)
        emb = torch.cat([torch.sin(emb), torch.cos(emb)], dim=1).view(num_embeddings, -1)
        if embedding_dim % 2 == 1:
            # zero pad
            emb = torch.cat([emb, torch.zeros(num_embeddings, 1)], dim=1)
        if padding_idx is not None:
            emb[padding_idx, :] = 0
        return emb

    def make_positions(self, x, padding_idx: int):
        mask = x.ne(padding_idx).int()
        return (torch.cumsum(mask, dim=1).type_as(mask) * mask).long() + padding_idx

    def forward(self, input):
        """Input is expected to be of size [bsz x seqlen]."""
        bsz, seq_len = input.size()
        max_pos = self.padding_idx + 1 + seq_len
        if self.weights is None or max_pos > self.weights.size(0):
            # recompute/expand embeddings if needed
            self.weights = PositionalEmbedding.get_embedding(
                max_pos, self.embedding_dim, self.padding_idx
            )
        self.weights = self.weights.to(self._float_tensor)
        positions = self.make_positions(input, self.padding_idx)
        return (
            self.weights.index_select(0, positions.view(-1))
            .view(bsz, seq_len, -1)
            .detach()
        )
    

class CLSPooling(nn.Module):
    def __init__(self, embed_dim, num_transformer_layers, dropout_rate):
        super().__init__()

        self.cls_token = nn.Parameter(torch.empty(1, 1, embed_dim))
        nn.init.normal_(self.cls_token, mean=0.0, std=0.25)

        self.transformer = nn.TransformerEncoder(
            nn.TransformerEncoderLayer(
                embed_dim,
                nhead=16 if embed_dim == 1024 else 8,
                dim_feedforward=4*embed_dim,
                dropout=dropout_rate,
                activation="relu",
                batch_first=True,
                norm_first=True
            ),
            num_layers=num_transformer_layers,
        )
    
        self.pos_emb = PositionalEmbedding(512, embed_dim, 1)
        self.scale = math.sqrt(embed_dim)

    def forward(self, x, lens):
        # x: [B, N, D]
        # lens: [B]

        # prepend cls token
        x = torch.cat(
            [
                self.cls_token.to(dtype=x.dtype, device=x.device).repeat(x.size(0), 1, 1), # B x 1 x D
                x
            ],
        dim=1) # [B, N+1, D]
        
        mask = lengths_to_padding_mask(lens+1)

        x = x + self.pos_emb(mask.long()) / self.scale
        
        x = self.transformer(x, src_key_padding_mask=mask) # [B, N+1, D]
        x = x[:, 0] # [B, D]
        return x


class CompressionAdapter(nn.Module):
    def __init__(self, cfg):
        super().__init__()
        self.embed_dim = cfg["embed_dim"]
        self.transformer_layers = cfg["transformer_layers"]
        self.dropout = cfg["dropout"]
        self.blank_idx = cfg["blank_idx"]
        self.sep_idx = cfg["sep_idx"]

        self.token_pooling_module = CLSPooling(
            self.embed_dim, self.transformer_layers, self.dropout
        )

    def char_compression(self, x, preds, lens):
        # x: B x T x D
        # preds: B x T
        # lens: B
        
        B, T, D = x.size()
        device = x.device
        dtype = x.dtype
        
        # zero-out the padding
        mask = lengths_to_padding_mask(lens) # B x T
        x = x.masked_fill(mask.unsqueeze(-1), 0)
        preds = preds.masked_fill(mask, self.blank_idx)

        # add a vector of -1 to know where each example ends after flattening the batch
        preds = torch.cat([-torch.ones(B, 1, device=device, dtype=torch.long), preds], dim=1).view(-1)
        x = torch.cat([torch.zeros(B, 1, D, device=device, dtype=dtype), x], dim=1).view(-1, D)

        # get points of consecutive preds
        preds, counts = preds.unique_consecutive(return_counts=True)
        
        # split in representations of same chars
        x = torch.split(x, counts.tolist())
        
        # remove blanks
        valid_mask = preds != self.blank_idx
        preds = preds[valid_mask]
        counts = counts[valid_mask] # [N]
        x = [x_i for x_i, v_i in zip(x, valid_mask) if v_i]
        
        # pack into tensor
        x = pad_sequence(x, batch_first=True, padding_value=0)
        
        # char pooling
        x = torch.sum(x, dim=1) / counts.to(dtype=x.dtype).unsqueeze(1) # [B, N, D] -> [B, D]

        # find split points for retrieving the examples
        split_points = (preds == -1).nonzero(as_tuple=True)[0]
        split_points = torch.cat([split_points, torch.tensor([len(preds)], device=device)])
        split_points = (split_points[1:] - split_points[:-1]).tolist()

        # split into examples
        x = torch.split(x, split_points)
        preds = torch.split(preds, split_points)
        lens = torch.tensor([len(x_i) for x_i in x], device=device)

        # pack into tensors
        x = pad_sequence(x, batch_first=True, padding_value=0)
        preds = pad_sequence(preds, batch_first=True, padding_value=self.blank_idx)

        # remove the parts we add to identify the bounds for each example
        x = x[:, 1:]
        preds = preds[:, 1:]
        lens -= 1

        mask = lengths_to_padding_mask(lens)
        
        # account for empty examples (just a sep token)
        empty_examples = lens == 0
        num_empty_examples = empty_examples.sum()
        if num_empty_examples > 0:
            mask[empty_examples, 0] = True
            lens[empty_examples] = 1
            preds[empty_examples, 0] = self.sep_idx
        
        return x, mask, lens, preds, num_empty_examples

    def token_compression(self, x, preds, lens):
        # x: B x T x D
        # preds: B x T
        # lens: B
        
        B, T, D = x.size()
        device = x.device
        dtype = x.dtype
        
        # new lengths after compression
        new_lens = preds.eq(self.sep_idx).sum(dim=1)
        
        # unpad and unpack to list of tensors
        preds = [preds[i, :lens[i]] for i in range(B)]
        x = [x[i, :lens[i]] for i in range(B)]
        
        # make sure every example ends with a separator
        num_examples_without_ending_sep = torch.tensor(0, device=device, dtype=torch.long)
        for i in range(B):
            if preds[i][-1] != self.sep_idx:
                preds[i] = torch.cat([preds[i], torch.tensor([self.sep_idx], device=device, dtype=torch.long)])
                x[i] = torch.cat([x[i], torch.zeros(1, D, device=device, dtype=dtype)])
                new_lens[i] += 1
                num_examples_without_ending_sep += 1
        
        # flatten
        preds = torch.cat(preds)
        x = torch.cat(x)
        
        # split points according to separators
        split_points = preds.eq(self.sep_idx).nonzero(as_tuple=True)[0] + 1
        split_points = torch.cat([torch.tensor([0], device=device, dtype=torch.long), split_points])
        split_points = (split_points[1:] - split_points[:-1]).tolist()
        
        # re-arrange in 3d [total_num_tokens x max(count) x D]
        x = torch.split(x, split_points) # Tuple[2d tensor]

        counts = torch.tensor([len(x_i) for x_i in x], device=device, dtype=torch.long)
        x = pad_sequence(x, batch_first=True, padding_value=0)
        
        # reduce dim 1
        x = self.token_pooling_module(x, counts)
        
        # reconstruct the batch
        split_points = new_lens.cumsum(dim=0)
        split_points = torch.cat([torch.tensor([0], device=device, dtype=torch.long), split_points])
        split_points = (split_points[1:] - split_points[:-1]).tolist()
        x = torch.split(x, split_points)
        x = pad_sequence(x, batch_first=True, padding_value=0) # B x ? x D
        
        mask = lengths_to_padding_mask(new_lens)
        
        return x, mask, new_lens, num_examples_without_ending_sep  

    def forward(self, x, preds, lens):
        x, mask, lens, preds, _ = self.char_compression(x, preds, lens)
        x, mask, lens, _ = self.token_compression(x, preds, lens)
        return x, mask, lens