1 files changed, 149 insertions, 20 deletions
diff --git a/swr2_asr/utils/decoder.py b/swr2_asr/utils/decoder.py
index fcddb79..1fd002a 100644
--- a/swr2_asr/utils/decoder.py
+++ b/swr2_asr/utils/decoder.py
@@ -1,26 +1,155 @@
 """Decoder for CTC-based ASR.""" ""
+import os
+from dataclasses import dataclass
+
 import torch
+from torchaudio.datasets.utils import _extract_tar
+from torchaudio.models.decoder import ctc_decoder
 
+from swr2_asr.utils.data import create_lexicon
 from swr2_asr.utils.tokenizer import CharTokenizer
 
 
-# TODO: refactor to use torch CTC decoder class
-def greedy_decoder(output, labels, label_lengths, tokenizer: CharTokenizer, collapse_repeated=True):
-    """Greedily decode a sequence."""
-    blank_label = tokenizer.get_blank_token()
-    arg_maxes = torch.argmax(output, dim=2)  # pylint: disable=no-member
-    decodes = []
-    targets = []
-    for i, args in enumerate(arg_maxes):
-        decode = []
-        targets.append(tokenizer.decode(labels[i][: label_lengths[i]].tolist()))
-        for j, index in enumerate(args):
-            if index != blank_label:
-                if collapse_repeated and j != 0 and index == args[j - 1]:
-                    continue
-                decode.append(index.item())
-        decodes.append(tokenizer.decode(decode))
-    return decodes, targets
-
-
-# TODO: add beam search decoder
+@dataclass
+class DecoderOutput:
+    """Decoder output."""
+
+    words: list[str]
+
+
+def decoder_factory(decoder_type: str = "greedy") -> callable:
+    """Decoder factory."""
+    if decoder_type == "greedy":
+        return get_greedy_decoder
+    if decoder_type == "lm":
+        return get_beam_search_decoder
+    raise NotImplementedError
+
+
+def get_greedy_decoder(
+    tokenizer: CharTokenizer,  # pylint: disable=redefined-outer-name
+    *_,
+):
+    """Greedy decoder."""
+    return GreedyDecoder(tokenizer)
+
+
+def get_beam_search_decoder(
+    tokenizer: CharTokenizer,  # pylint: disable=redefined-outer-name
+    hparams: dict,  # pylint: disable=redefined-outer-name
+):
+    """Beam search decoder."""
+    hparams = hparams.get("lm", {})
+    language, lang_model_path, n_gram, beam_size, beam_threshold, n_best, lm_weight, word_score = (
+        hparams["language"],
+        hparams["language_model_path"],
+        hparams["n_gram"],
+        hparams["beam_size"],
+        hparams["beam_threshold"],
+        hparams["n_best"],
+        hparams["lm_weight"],
+        hparams["word_score"],
+    )
+
+    if not os.path.isdir(os.path.join(lang_model_path, f"mls_lm_{language}")):
+        url = f"https://dl.fbaipublicfiles.com/mls/mls_lm_{language}.tar.gz"
+        torch.hub.download_url_to_file(url, f"data/mls_lm_{language}.tar.gz")
+        _extract_tar("data/mls_lm_{language}.tar.gz", overwrite=True)
+
+    tokens_path = os.path.join(lang_model_path, f"mls_lm_{language}", "tokens.txt")
+    if not os.path.isfile(tokens_path):
+        tokenizer.create_tokens_txt(tokens_path)
+
+    lexicon_path = os.path.join(lang_model_path, f"mls_lm_{language}", "lexicon.txt")
+    if not os.path.isfile(lexicon_path):
+        occurences_path = os.path.join(lang_model_path, f"mls_lm_{language}", "vocab_counts.txt")
+        create_lexicon(occurences_path, lexicon_path)
+
+    lm_path = os.path.join(lang_model_path, f"mls_lm_{language}", f"{n_gram}-gram_lm.arpa")
+
+    decoder = ctc_decoder(
+        lexicon=lexicon_path,
+        tokens=tokens_path,
+        lm=lm_path,
+        blank_token="_",
+        sil_token="<SPACE>",
+        unk_word="<UNK>",
+        nbest=n_best,
+        beam_size=beam_size,
+        beam_threshold=beam_threshold,
+        lm_weight=lm_weight,
+        word_score=word_score,
+    )
+    return decoder
+
+
+class GreedyDecoder:
+    """Greedy decoder."""
+
+    def __init__(self, tokenizer: CharTokenizer):  # pylint: disable=redefined-outer-name
+        self.tokenizer = tokenizer
+
+    def __call__(
+        self, output, greedy_type: str = "inference", labels=None, label_lengths=None
+    ):  # pylint: disable=redefined-outer-name
+        """Greedily decode a sequence."""
+        if greedy_type == "train":
+            res = self.train(output, labels, label_lengths)
+        if greedy_type == "inference":
+            res = self.inference(output)
+
+        res = [x.split(" ") for x in res]
+        res = [[DecoderOutput(x)] for x in res]
+        return res
+
+    def train(self, output, labels, label_lengths):
+        """Greedily decode a sequence with known labels."""
+        blank_label = tokenizer.get_blank_token()
+        arg_maxes = torch.argmax(output, dim=2)  # pylint: disable=no-member
+        decodes = []
+        targets = []
+        for i, args in enumerate(arg_maxes):
+            decode = []
+            targets.append(self.tokenizer.decode(labels[i][: label_lengths[i]].tolist()))
+            for j, index in enumerate(args):
+                if index != blank_label:
+                    if j != 0 and index == args[j - 1]:
+                        continue
+                    decode.append(index.item())
+            decodes.append(self.tokenizer.decode(decode))
+        return decodes, targets
+
+    def inference(self, output):
+        """Greedily decode a sequence."""
+        collapse_repeated = True
+        arg_maxes = torch.argmax(output, dim=2)  # pylint: disable=no-member
+        blank_label = self.tokenizer.get_blank_token()
+        decodes = []
+        for args in arg_maxes:
+            decode = []
+            for j, index in enumerate(args):
+                if index != blank_label:
+                    if collapse_repeated and j != 0 and index == args[j - 1]:
+                        continue
+                    decode.append(index.item())
+            decodes.append(self.tokenizer.decode(decode))
+
+        return decodes
+
+
+if __name__ == "__main__":
+    tokenizer = CharTokenizer.from_file("data/tokenizers/char_tokenizer_german.json")
+    tokenizer.create_tokens_txt("data/tokenizers/tokens_german.txt")
+
+    hparams = {
+        "language": "german",
+        "lang_model_path": "data",
+        "n_gram": 3,
+        "beam_size": 100,
+        "beam_threshold": 100,
+        "n_best": 1,
+        "lm_weight": 0.5,
+        "word_score": 1.0,
+    }
+
+    get_beam_search_decoder(tokenizer, hparams)