# Copyright (c) 2021, EleutherAI
# This file is based on code by the authors denoted below and has been modified from its original version.
#
# Copyright 2018 The Open AI Team Authors and The HuggingFace Inc. team.
#
# 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.

"""Tokenization classes for OpenAI GPT."""

from __future__ import absolute_import, division, print_function, unicode_literals

import sys
import json
import logging
import os
import regex as re
from io import open

from functools import lru_cache


logger = logging.getLogger(__name__)

PRETRAINED_VOCAB_ARCHIVE_MAP = {
    "gpt2": "https://s3.amazonaws.com/models.huggingface.co/bert/gpt2-vocab.json",
}
PRETRAINED_MERGES_ARCHIVE_MAP = {
    "gpt2": "https://s3.amazonaws.com/models.huggingface.co/bert/gpt2-merges.txt",
}
PRETRAINED_VOCAB_POSITIONAL_EMBEDDINGS_SIZE_MAP = {
    "gpt2": 1024,
}

VOCAB_NAME = "vocab.json"
MERGES_NAME = "merges.txt"
SPECIAL_TOKENS_NAME = "special_tokens.txt"


@lru_cache()
def bytes_to_unicode():
    """
    Returns list of utf-8 byte and a corresponding list of unicode strings.
    The reversible bpe codes work on unicode strings.
    This means you need a large # of unicode characters in your vocab if you want to avoid UNKs.
    When you're at something like a 10B token dataset you end up needing around 5K for decent coverage.
    This is a significant percentage of your normal, say, 32K bpe vocab.
    To avoid that, we want lookup tables between utf-8 bytes and unicode strings.
    And avoids mapping to whitespace/control characters the bpe code barfs on.
    """
    _chr = unichr if sys.version_info[0] == 2 else chr
    bs = (
        list(range(ord("!"), ord("~") + 1))
        + list(range(ord("¡"), ord("¬") + 1))
        + list(range(ord("®"), ord("ÿ") + 1))
    )
    cs = bs[:]
    n = 0
    for b in range(2**8):
        if b not in bs:
            bs.append(b)
            cs.append(2**8 + n)
            n += 1
    cs = [_chr(n) for n in cs]
    return dict(zip(bs, cs))


def get_pairs(word):
    """Return set of symbol pairs in a word.

    Word is represented as tuple of symbols (symbols being variable-length strings).
    """
    pairs = set()
    prev_char = word[0]
    for char in word[1:]:
        pairs.add((prev_char, char))
        prev_char = char
    return pairs


class GPT2Tokenizer(object):
    """
    GPT-2 BPE tokenizer. Peculiarities:
        - Byte-level BPE
    """

    @classmethod
    def from_pretrained(
        cls, pretrained_model_name_or_path, cache_dir=None, *inputs, **kwargs
    ):
        """
        Instantiate a PreTrainedBertModel from a pre-trained model file.
        Download and cache the pre-trained model file if needed.
        """
        if pretrained_model_name_or_path in PRETRAINED_VOCAB_ARCHIVE_MAP:
            vocab_file = PRETRAINED_VOCAB_ARCHIVE_MAP[pretrained_model_name_or_path]
            merges_file = PRETRAINED_MERGES_ARCHIVE_MAP[pretrained_model_name_or_path]
            special_tokens_file = None
        else:
            vocab_file = os.path.join(pretrained_model_name_or_path, VOCAB_NAME)
            merges_file = os.path.join(pretrained_model_name_or_path, MERGES_NAME)
            special_tokens_file = os.path.join(
                pretrained_model_name_or_path, SPECIAL_TOKENS_NAME
            )
            if not os.path.exists(special_tokens_file):
                special_tokens_file = None
            else:
                logger.info(
                    "loading special tokens file {}".format(special_tokens_file)
                )
        # redirect to the cache, if necessary
        try:
            from .file_utils import cached_path

            resolved_vocab_file = cached_path(vocab_file, cache_dir=cache_dir)
            resolved_merges_file = cached_path(merges_file, cache_dir=cache_dir)
        except EnvironmentError:
            logger.error(
                "Model name '{}' was not found in model name list ({}). "
                "We assumed '{}' was a path or url but couldn't find files {} and {} "
                "at this path or url.".format(
                    pretrained_model_name_or_path,
                    ", ".join(PRETRAINED_VOCAB_ARCHIVE_MAP.keys()),
                    pretrained_model_name_or_path,
                    vocab_file,
                    merges_file,
                )
            )
            return None
        if resolved_vocab_file == vocab_file and resolved_merges_file == merges_file:
            logger.info("loading vocabulary file {}".format(vocab_file))
            logger.info("loading merges file {}".format(merges_file))
        else:
            logger.info(
                "loading vocabulary file {} from cache at {}".format(
                    vocab_file, resolved_vocab_file
                )
            )
            logger.info(
                "loading merges file {} from cache at {}".format(
                    merges_file, resolved_merges_file
                )
            )
        if (
            pretrained_model_name_or_path
            in PRETRAINED_VOCAB_POSITIONAL_EMBEDDINGS_SIZE_MAP
        ):
            # if we're using a pretrained model, ensure the tokenizer won't index sequences longer
            # than the number of positional embeddings
            max_len = PRETRAINED_VOCAB_POSITIONAL_EMBEDDINGS_SIZE_MAP[
                pretrained_model_name_or_path
            ]
            kwargs["max_len"] = min(kwargs.get("max_len", int(1e12)), max_len)
        # Instantiate tokenizer.
        if special_tokens_file and "special_tokens" not in kwargs:
            special_tokens = (
                open(special_tokens_file, encoding="utf-8").read().split("\n")[:-1]
            )
        else:
            special_tokens = kwargs.pop("special_tokens", [])
        tokenizer = cls(
            resolved_vocab_file,
            resolved_merges_file,
            special_tokens=special_tokens,
            *inputs,
            **kwargs
        )
        return tokenizer

    def __init__(
        self,
        vocab_file,
        merges_file,
        errors="replace",
        special_tokens=None,
        max_len=None,
    ):
        self.max_len = max_len if max_len is not None else int(1e12)
        self.encoder = json.load(open(vocab_file))
        self.decoder = {v: k for k, v in self.encoder.items()}
        self.errors = errors  # how to handle errors in decoding
        self.byte_encoder = bytes_to_unicode()
        self.byte_decoder = {v: k for k, v in self.byte_encoder.items()}
        bpe_data = open(merges_file, encoding="utf-8").read().split("\n")[1:-1]
        bpe_merges = [tuple(merge.split()) for merge in bpe_data]
        self.bpe_ranks = dict(zip(bpe_merges, range(len(bpe_merges))))

        # Should haved added re.IGNORECASE so BPE merges can happen for
        # capitalized versions of contractions
        self.pat = re.compile(
            r"""'s|'t|'re|'ve|'m|'ll|'d| ?\p{L}+| ?\p{N}+| ?[^\s\p{L}\p{N}]+|\s+(?!\S)|\s+"""
        )

        self.special_tokens = {}
        self.special_tokens_decoder = {}
        self.set_special_tokens(special_tokens)

    def __len__(self):
        return len(self.encoder) + len(self.special_tokens)

    def set_special_tokens(self, special_tokens):
        """Add a list of additional tokens to the encoder.
        The additional tokens are indexed starting from the last index of the
        current vocabulary in the order of the `special_tokens` list.
        """
        if not special_tokens:
            self.special_tokens = {}
            self.special_tokens_decoder = {}
            return
        self.special_tokens = dict(
            (tok, len(self.encoder) + i) for i, tok in enumerate(special_tokens)
        )
        self.special_tokens_decoder = {v: k for k, v in self.special_tokens.items()}
        logger.info("Special tokens {}".format(self.special_tokens))

    @lru_cache(maxsize=131072)
    def bpe(self, token):
        word = tuple(token)
        pairs = get_pairs(word)

        if not pairs:
            return token

        while True:
            bigram = min(pairs, key=lambda pair: self.bpe_ranks.get(pair, float("inf")))
            if bigram not in self.bpe_ranks:
                break
            first, second = bigram
            new_word = []
            i = 0
            while i < len(word):
                try:
                    j = word.index(first, i)
                    new_word.extend(word[i:j])
                    i = j
                except BaseException:
                    new_word.extend(word[i:])
                    break

                if word[i] == first and i < len(word) - 1 and word[i + 1] == second:
                    new_word.append(first + second)
                    i += 2
                else:
                    new_word.append(word[i])
                    i += 1
            new_word = tuple(new_word)
            word = new_word
            if len(word) == 1:
                break
            else:
                pairs = get_pairs(word)
        word = " ".join(word)
        return word

    def tokenize(self, text):
        """Tokenize a string."""
        bpe_tokens = []
        for token in re.findall(self.pat, text):
            if sys.version_info[0] == 2:
                token = "".join(self.byte_encoder[ord(b)] for b in token)
            else:
                token = "".join(self.byte_encoder[b] for b in token.encode("utf-8"))
            bpe_tokens.extend(bpe_token for bpe_token in self.bpe(token).split(" "))
        return bpe_tokens

    def convert_tokens_to_ids(self, tokens):
        """Converts a sequence of tokens into ids using the vocab."""
        ids = []
        if isinstance(tokens, str) or (
            sys.version_info[0] == 2 and isinstance(tokens, unicode)
        ):
            if tokens in self.special_tokens:
                return self.special_tokens[tokens]
            else:
                return self.encoder.get(tokens, 0)
        for token in tokens:
            if token in self.special_tokens:
                ids.append(self.special_tokens[token])
            else:
                ids.append(self.encoder.get(token, 0))
        if len(ids) > self.max_len:
            logger.warning(
                "Token indices sequence length is longer than the specified maximum "
                " sequence length for this OpenAI GPT model ({} > {}). Running this"
                " sequence through the model will result in indexing errors".format(
                    len(ids), self.max_len
                )
            )
        return ids

    def convert_ids_to_tokens(self, ids, skip_special_tokens=False):
        """Converts a sequence of ids in BPE tokens using the vocab."""
        tokens = []
        for i in ids:
            if i in self.special_tokens_decoder:
                if not skip_special_tokens:
                    tokens.append(self.special_tokens_decoder[i])
            else:
                tokens.append(self.decoder[i])
        return tokens

    def encode(self, text):
        return self.convert_tokens_to_ids(self.tokenize(text))

    def decode(self, tokens):
        text = "".join([self.decoder[token] for token in tokens])
        text = bytearray([self.byte_decoder[c] for c in text]).decode(
            "utf-8", errors=self.errors
        )
        return text

    def save_vocabulary(self, vocab_path):
        """Save the tokenizer vocabulary and merge files to a directory."""
        if not os.path.isdir(vocab_path):
            logger.error(
                "Vocabulary path ({}) should be a directory".format(vocab_path)
            )
            return
        vocab_file = os.path.join(vocab_path, VOCAB_NAME)
        merge_file = os.path.join(vocab_path, MERGES_NAME)
        special_tokens_file = os.path.join(vocab_path, SPECIAL_TOKENS_NAME)

        with open(vocab_file, "w", encoding="utf-8") as f:
            f.write(json.dumps(self.encoder, ensure_ascii=False))

        index = 0
        with open(merge_file, "w", encoding="utf-8") as writer:
            writer.write("#version: 0.2\n")
            for bpe_tokens, token_index in sorted(
                self.bpe_ranks.items(), key=lambda kv: kv[1]
            ):
                if index != token_index:
                    logger.warning(
                        "Saving vocabulary to {}: BPE merge indices are not consecutive."
                        " Please check that the tokenizer is not corrupted!".format(
                            merge_file
                        )
                    )
                    index = token_index
                writer.write(" ".join(bpe_tokens) + "\n")
                index += 1

        index = len(self.encoder)
        with open(special_tokens_file, "w", encoding="utf-8") as writer:
            for token, token_index in sorted(
                self.special_tokens.items(), key=lambda kv: kv[1]
            ):
                if index != token_index:
                    logger.warning(
                        "Saving special tokens vocabulary to {}: BPE indices are not consecutive."
                        " Please check that the tokenizer is not corrupted!".format(
                            special_tokens_file
                        )
                    )
                    index = token_index
                writer.write(token + "\n")
                index += 1

        return vocab_file, merge_file, special_tokens_file