#!/usr/bin/env python3
# -*- coding: utf-8 -*-
#
# Copyright 2016-2099 Ailemon.net
#
# This file is part of ASRT Speech Recognition Tool.
#
# ASRT is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# ASRT is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with ASRT.  If not, see <https://www.gnu.org/licenses/>.
# ============================================================================

"""
@author: nl8590687
ASRT语音识别的语言模型

基于N-Gram的语言模型
"""

import os

from utils.ops import get_symbol_dict, get_language_model

class ModelLanguage:
    '''
    ASRT专用N-Gram语言模型
    '''
    def __init__(self, model_path: str):
        self.model_path = model_path
        self.dict_pinyin = dict()
        self.model1 = dict()
        self.model2 = dict()

    def load_model(self):
        '''
        加载N-Gram语言模型到内存
        '''
        self.dict_pinyin = get_symbol_dict('dict.txt')
        self.model1 = get_language_model(os.path.join(self.model_path, 'language_model1.txt'))
        self.model2 = get_language_model(os.path.join(self.model_path, 'language_model2.txt'))
        model = (self.dict_pinyin, self.model1, self.model2 )
        return model

    def pinyin_to_text(self, list_pinyin: list, beam_size: int=100) -> str:
        '''
        拼音转文本，一次性取得全部结果
        '''
        result = list()
        tmp_result_last = list()
        for item_pinyin in list_pinyin:
            tmp_result = self.pinyin_stream_decode(tmp_result_last, item_pinyin, beam_size)
            if len(tmp_result) == 0 and len(tmp_result_last) > 0:
                result.append(tmp_result_last[0][0])
                tmp_result = self.pinyin_stream_decode([], item_pinyin, beam_size)
                if len(tmp_result) > 0:
                    result.append(tmp_result[0][0])
                tmp_result = []
            tmp_result_last = tmp_result

        if len(tmp_result_last) > 0:
            result.append(tmp_result_last[0][0])

        return ''.join(result)

    def pinyin_stream_decode(self, temple_result: list,
                            item_pinyin: str,
                            beam_size: int = 100) -> list:
        '''
        拼音流式解码，逐字转换，每次返回中间结果
        '''
        # 如果这个拼音不在汉语拼音字典里的话，直接返回空列表，不做decode
        if item_pinyin not in self.dict_pinyin:
            return []

        # 获取拼音下属的字的列表，cur_words包含了该拼音对应的所有的字
        cur_words = self.dict_pinyin[item_pinyin]
        # 第一个字做初始处理
        if len(temple_result) == 0:
            lst_result = list()
            for word in cur_words:
                # 添加该字到可能的句子列表，设置初始概率为1.0
                lst_result.append([word, 1.0])
            return lst_result

        # 开始处理已经至少有一个字的中间结果情况
        new_result = list()
        for sequence in temple_result:
            for cur_word in cur_words:
                # 得到2-gram的汉字子序列
                tuple2_word = sequence[0][-1] + cur_word
                if tuple2_word not in self.model2:
                    # 如果2-gram子序列不存在
                    continue
                # 计算状态转移概率
                prob_origin = sequence[1] # 原始概率
                count_two_word = float(self.model2[tuple2_word]) # 二字频数
                count_one_word = float(self.model1[tuple2_word[-2]]) # 单字频数
                cur_probility = prob_origin * count_two_word / count_one_word
                new_result.append([sequence[0]+cur_word, cur_probility])

        new_result = sorted(new_result, key=lambda x:x[1], reverse=True)
        if len(new_result) > beam_size:
            return new_result[0:beam_size]
        return new_result


if __name__=='__main__':
    ml = ModelLanguage('model_language')
    ml.load_model()

    _str_pinyin = ['zhe4', 'zhen1', 'shi4', 'ji2', 'hao3', 'de5']
    _RESULT = ml.pinyin_to_text(_str_pinyin)
    print('语音转文字结果:\n', _RESULT)