# Copyright (c) 2020 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.

from typing import Dict, Iterable, List
from collections import OrderedDict

__all__ = ["Vocab"]


class Vocab(object):
    """  Vocabulary.

    Parameters
    -----------
    symbols: Iterable[str]
        Common symbols.
    
    padding_symbol: str, optional
        Symbol for pad. Defaults to "<pad>".

    unk_symbol: str, optional
        Symbol for unknow. Defaults to "<unk>"
    
    start_symbol: str, optional
        Symbol for start. Defaults to "<s>"

    end_symbol: str, optional
        Symbol for end. Defaults to "</s>"
    """

    def __init__(self,
                 symbols: Iterable[str],
                 padding_symbol="<pad>",
                 unk_symbol="<unk>",
                 start_symbol="<s>",
                 end_symbol="</s>"):
        self.special_symbols = OrderedDict()
        for i, item in enumerate(
            [padding_symbol, unk_symbol, start_symbol, end_symbol]):
            if item:
                self.special_symbols[item] = len(self.special_symbols)

        self.padding_symbol = padding_symbol
        self.unk_symbol = unk_symbol
        self.start_symbol = start_symbol
        self.end_symbol = end_symbol

        self.stoi = OrderedDict()
        self.stoi.update(self.special_symbols)

        for i, s in enumerate(symbols):
            if s not in self.stoi:
                self.stoi[s] = len(self.stoi)
        self.itos = {v: k for k, v in self.stoi.items()}

    def __len__(self):
        return len(self.stoi)

    @property
    def num_specials(self):
        """ The number of special symbols.
        """
        return len(self.special_symbols)

    # special tokens
    @property
    def padding_index(self):
        """ The index of padding symbol
        """
        return self.stoi.get(self.padding_symbol, -1)

    @property
    def unk_index(self):
        """The index of unknow symbol.
        """
        return self.stoi.get(self.unk_symbol, -1)

    @property
    def start_index(self):
        """The index of start symbol.
        """
        return self.stoi.get(self.start_symbol, -1)

    @property
    def end_index(self):
        """ The index of end symbol.
        """
        return self.stoi.get(self.end_symbol, -1)

    def __repr__(self):
        fmt = "Vocab(size: {},\nstoi:\n{})"
        return fmt.format(len(self), self.stoi)

    def __str__(self):
        return self.__repr__()

    def lookup(self, symbol):
        """ The index that symbol correspond.
        """
        return self.stoi[symbol]

    def reverse(self, index):
        """ The symbol thar index cottespond.
        """
        return self.itos[index]

    def add_symbol(self, symbol):
        """ Add a new symbol in vocab.
        """
        if symbol in self.stoi:
            return
        N = len(self.stoi)
        self.stoi[symbol] = N
        self.itos[N] = symbol

    def add_symbols(self, symbols):
        """ Add multiple symbols in vocab.
        """
        for symbol in symbols:
            self.add_symbol(symbol)