from __future__ import annotations

import os
from pathlib import Path
from typing import List, Optional, Union

from tokenizers import Tokenizer as BaseTokenizer

from .aliases import PathOrStr
from .config import ModelConfig, TokenizerConfig, TrainConfig, TruncationDirection
from .exceptions import InstellaConfigurationError

__all__ = ["Tokenizer"]


class Tokenizer:
    """
    A :class:`Tokenizer` is a light-weight wrapper around a HuggingFace :class:`tokenizers.Tokenizer`.

    :param base_tokenizer: The :class:`tokenizers.Tokenizer` to use.
    :param eos_token_id: The token ID corresponding to the "end-of-sentence" token.
    :param truncate_to: Truncate when tokenizing to this number of token IDs.
    :param truncate_direction: The direction to truncate in. "right" means truncate the tokens
        on the right. "left" means truncate the tokens on the left. If ``truncate_to`` is null,
        this setting has no effect.
    """

    def __init__(
        self,
        base_tokenizer: BaseTokenizer,
        eos_token_id: int,
        pad_token_id: Optional[int] = None,
        truncate_to: Optional[int] = None,
        truncate_direction: Union[str, TruncationDirection] = TruncationDirection.right,
    ):
        self.base_tokenizer = base_tokenizer
        self.base_tokenizer.no_truncation()
        self.eos_token_id = eos_token_id
        self.pad_token_id = pad_token_id if pad_token_id is not None else eos_token_id
        self.truncate_to = truncate_to
        self.truncate_direction = TruncationDirection(truncate_direction)

    @property
    def vocab_size(self) -> int:
        return self.base_tokenizer.get_vocab_size()

    @property
    def eos_token(self) -> str:
        return self.decode([self.eos_token_id], skip_special_tokens=False)

    @property
    def pad_token(self) -> str:
        return self.decode([self.pad_token_id], skip_special_tokens=False)

    @classmethod
    def from_train_config(cls, config: TrainConfig) -> Tokenizer:
        tokenizer_identifier = config.tokenizer.identifier
        if Path(tokenizer_identifier).is_file():
            tokenizer = cls.from_file(
                tokenizer_identifier,
                eos_token_id=config.model.eos_token_id,
                pad_token_id=config.model.pad_token_id,
            )
        else:
            tokenizer = cls.from_pretrained(
                tokenizer_identifier,
                eos_token_id=config.model.eos_token_id,
                pad_token_id=config.model.pad_token_id,
            )
        if config.model.vocab_size != tokenizer.vocab_size:
            raise InstellaConfigurationError("vocab size mismatch between config and tokenizer")
        return tokenizer

    @classmethod
    def from_pretrained(cls, identifier: str, **kwargs) -> Tokenizer:
        """
        Initialize a tokenizer from a pretrained tokenizer on the HuggingFace Hub.

        :param identifier: The identifier of a model on the Hub that contains a
            ``tokenizer.json`` file.
        :param kwargs: Other key word arguments passed to :class:`Tokenizer`.
        """
        base_tokenizer = BaseTokenizer.from_pretrained(identifier)
        eos_token_id = kwargs.pop("eos_token_id", base_tokenizer.get_vocab_size() - 1)
        return cls(base_tokenizer, eos_token_id, **kwargs)

    @classmethod
    def from_file(cls, filename: PathOrStr, **kwargs) -> Tokenizer:
        """
        Initialize a tokenizer from a file.

        You can create those files with ``BaseTokenizer.save()``.

        :param filename: The name of a file containing a tokenizer specification.
        :param kwargs: Other key word arguments passed to :class:`Tokenizer`.
        """
        base_tokenizer = BaseTokenizer.from_file(filename)
        eos_token_id = kwargs.pop("eos_token_id", base_tokenizer.get_vocab_size() - 1)
        return cls(base_tokenizer, eos_token_id, **kwargs)

    @classmethod
    def from_checkpoint(cls, checkpoint_dir: PathOrStr) -> Tokenizer:
        """
        Load a tokenizer from a checkpoint.
        """
        from cached_path import cached_path

        # Load configs.
        config_path = cached_path(os.path.join(checkpoint_dir, "config.yaml"))
        tokenizer_config = TokenizerConfig.load(config_path, key="tokenizer")
        model_config = ModelConfig.load(config_path, key="model")

        # Initialize tokenizer and validate vocab size.
        if Path(tokenizer_config.identifier).is_file():
            tokenizer = cls.from_file(
                tokenizer_config.identifier,
                eos_token_id=model_config.eos_token_id,
                pad_token_id=model_config.pad_token_id,
            )
        else:
            tokenizer = cls.from_pretrained(
                tokenizer_config.identifier,
                eos_token_id=model_config.eos_token_id,
                pad_token_id=model_config.pad_token_id,
            )
        if model_config.vocab_size != tokenizer.vocab_size:
            raise InstellaConfigurationError("vocab size mismatch between config and tokenizer")
        return tokenizer

    def add_special_tokens(self, input_ids: List[int]) -> List[int]:
        """
        Add special tokens in-place (if not already present) to the given token IDs.
        """
        if not input_ids or input_ids[-1] != self.eos_token_id:
            input_ids.append(self.eos_token_id)
        return input_ids

    def num_special_tokens_to_add(self, is_pair: bool = False) -> int:
        return 2 if is_pair else 1

    def _truncate(
        self, input_ids: List[int], truncate_to: Optional[int], direction: TruncationDirection
    ) -> list[int]:
        if truncate_to is None or len(input_ids) <= truncate_to:
            return input_ids
        elif direction == TruncationDirection.left:
            return input_ids[len(input_ids) - truncate_to :]
        else:
            return input_ids[: -(len(input_ids) - truncate_to)]

    def encode(self, input: str, add_special_tokens: bool = True) -> List[int]:
        """
        Encode a string into token IDs.
        """
        return self.encode_batch([input], add_special_tokens=add_special_tokens)[0]

    def encode_batch(self, inputs: List[str], add_special_tokens: bool = True) -> List[List[int]]:
        """
        Encode a batch of strings into token IDs.
        """
        truncate_to = self.truncate_to
        if truncate_to is not None and add_special_tokens:
            truncate_to -= self.num_special_tokens_to_add(False)

        batch_encoding = self.base_tokenizer.encode_batch(inputs)

        all_input_ids = []
        for encoding in batch_encoding:
            input_ids = self._truncate(encoding.ids, truncate_to, self.truncate_direction)
            if add_special_tokens:
                input_ids = self.add_special_tokens(input_ids)
            all_input_ids.append(input_ids)

        return all_input_ids

    def decode(self, token_ids: List[int], skip_special_tokens: bool = True) -> str:
        """
        Decode a list of token IDs to a string.
        """
        return self.base_tokenizer.decode(token_ids, skip_special_tokens=skip_special_tokens)
