PaddleSpeech/runtime/engine/asr/decoder/ctc_prefix_beam_search_decoder.h

// Copyright (c) 2020 Mobvoi Inc (Binbin Zhang)
// Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// modified from
// https://github.com/wenet-e2e/wenet/blob/main/runtime/core/decoder/ctc_prefix_beam_search.cc

#pragma once

#include "decoder/ctc_beam_search_opt.h"
#include "decoder/ctc_prefix_beam_search_score.h"
#include "decoder/decoder_itf.h"
#include "fst/symbol-table.h"

namespace ppspeech {
class ContextGraph;
class CTCPrefixBeamSearch : public DecoderBase {
  public:
    CTCPrefixBeamSearch(const std::string& vocab_path,
                        const CTCBeamSearchOptions& opts);
    ~CTCPrefixBeamSearch() {}

    SearchType Type() const { return SearchType::kPrefixBeamSearch; }

    void InitDecoder() override;

    void Reset() override;

    void AdvanceDecode(
        const std::shared_ptr<kaldi::DecodableInterface>& decodable) override;

    std::string GetFinalBestPath() override;
    std::string GetPartialResult() override;

    void FinalizeSearch();

    const std::shared_ptr<fst::SymbolTable> WordSymbolTable() const override {
        return unit_table_;
    }

    const std::vector<std::vector<int>>& Inputs() const { return hypotheses_; }
    const std::vector<std::vector<int>>& Outputs() const { return outputs_; }
    const std::vector<float>& Likelihood() const { return likelihood_; }
    const std::vector<float>& ViterbiLikelihood() const {
        return viterbi_likelihood_;
    }
    const std::vector<std::vector<int>>& Times() const { return times_; }

  protected:
    std::string GetBestPath() override;
    std::vector<std::pair<double, std::string>> GetNBestPath() override;
    std::vector<std::pair<double, std::string>> GetNBestPath(int n) override;

  private:
    std::string GetBestPath(int index);

    void AdvanceDecoding(
        const std::vector<std::vector<kaldi::BaseFloat>>& logp);

    void UpdateOutputs(const std::pair<std::vector<int>, PrefixScore>& prefix);
    void UpdateHypotheses(
        const std::vector<std::pair<std::vector<int>, PrefixScore>>& prefix);
    void UpdateFinalContext();


  private:
    CTCBeamSearchOptions opts_;
    std::shared_ptr<fst::SymbolTable> unit_table_{nullptr};

    std::unordered_map<std::vector<int>, PrefixScore, PrefixScoreHash>
        cur_hyps_;

    // n-best list and corresponding likelihood, in sorted order
    std::vector<std::vector<int>> hypotheses_;
    std::vector<float> likelihood_;

    std::vector<std::vector<int>> times_;
    std::vector<float> viterbi_likelihood_;

    // Outputs contain the hypotheses_ and tags lik: <context> and </context>
    std::vector<std::vector<int>> outputs_;

    std::shared_ptr<ContextGraph> context_graph_{nullptr};

    DISALLOW_COPY_AND_ASSIGN(CTCPrefixBeamSearch);
};


}  // namespace ppspeech