# Copyright The Lightning 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.
import math
import os
from collections import Counter, defaultdict
from typing import TYPE_CHECKING, Any, Callable, Optional, Union

import torch
from torch import Tensor
from torch.utils.data import DataLoader, Dataset

from torchmetrics.utilities.data import _cumsum
from torchmetrics.utilities.imports import _TQDM_AVAILABLE, _TRANSFORMERS_GREATER_EQUAL_4_4

if TYPE_CHECKING:
    if _TQDM_AVAILABLE:
        import tqdm
    if _TRANSFORMERS_GREATER_EQUAL_4_4:
        from transformers import PreTrainedModel, PreTrainedTokenizerBase


def _process_attention_mask_for_special_tokens(attention_mask: Tensor) -> Tensor:
    """Process attention mask to be zero for special [CLS] and [SEP] tokens as they're not included in BERT score.

    Args:
        attention_mask: An attention mask to be returned, for example, by a `transformers` tokenizer.

    Return:
        A processed attention mask.

    """
    # Make attention_mask zero for [CLS] token
    attention_mask[:, 0] = 0
    # Make attention_mask zero for [SEP] token
    sep_token_position = _cumsum((attention_mask - 0.1), dim=-1).argmax(-1)
    attention_mask[torch.arange(attention_mask.size(0)).long(), sep_token_position] = 0
    return attention_mask


def _input_data_collator(
    batch: dict[str, Tensor], device: Optional[Union[str, torch.device]] = None
) -> dict[str, Tensor]:
    """Trim model inputs.

    This function trims the model inputs to the longest sequence within the batch and put the input on the proper
    device.

    """
    max_len = int(batch["attention_mask"].sum(1).max().item())
    input_ids = batch["input_ids"][:, :max_len].to(device)
    attention_mask = batch["attention_mask"][:, :max_len].to(device)
    batch.update({"input_ids": input_ids, "attention_mask": attention_mask})
    return batch


def _output_data_collator(model_output: Tensor, attention_mask: Tensor, target_len: int) -> tuple[Tensor, Tensor]:
    """Pad the model output and attention mask to the target length."""
    zeros_shape = list(model_output.shape)
    zeros_shape[2] = target_len - zeros_shape[2]
    model_output = torch.cat(
        [model_output, torch.zeros(zeros_shape, dtype=model_output.dtype).to(model_output.device)], dim=2
    )
    zeros = torch.zeros(zeros_shape[0], zeros_shape[2], dtype=attention_mask.dtype).to(attention_mask.device)
    attention_mask = torch.cat([attention_mask, zeros], dim=1)
    return model_output, attention_mask


def _sort_data_according_length(input_ids: Tensor, attention_mask: Tensor) -> tuple[Tensor, Tensor, Tensor]:
    """Sort tokenized sentence from the shortest to the longest one."""
    sorted_indices = attention_mask.sum(1).argsort()
    input_ids = input_ids[sorted_indices]
    attention_mask = attention_mask[sorted_indices]
    return input_ids, attention_mask, sorted_indices


def _preprocess_text(
    text: list[str],
    tokenizer: Any,
    max_length: int = 512,
    truncation: bool = True,
    sort_according_length: bool = True,
    own_tokenizer: bool = False,
) -> tuple[dict[str, Tensor], Optional[Tensor]]:
    """Text pre-processing function using `transformers` `AutoTokenizer` instance.

    Args:
        text:
            An iterable of sentences.
        tokenizer:
            Either `AutoTokenizer` instance from `transformers` package, or a user's own tokenizer.
        max_length:
            A maximum sequence length.
        truncation:
            An indication of whether tokenized sequences should be padded only to the length of the longest sequence.
        sort_according_length:
            An indication of whether tokenized sequences should be sorted from shortest to longest. This is appropriate
            to do for leveraging dynamic padding during embedding calculation and thereby to hasten inference.
        own_tokenizer:
            An indication of whether a non-default user's own tokenizer is used.

    Return:
        A dictionary of tokenized sentences including input_ids and attention_mask.

    Raises:
        BaseException:
            If a tokenization with a user's own tokenizer is not successful.

    """
    if not own_tokenizer:
        tokenized_data = tokenizer(
            text, padding="max_length", max_length=max_length, truncation=truncation, return_tensors="pt"
        )
    else:
        try:
            tokenized_data = tokenizer(text, max_length)
        except BaseException as ex:
            raise RuntimeError(f"Tokenization was not successful: {ex}") from ex

    if sort_according_length:
        input_ids, attention_mask, sorting_indices = _sort_data_according_length(
            tokenized_data["input_ids"], tokenized_data["attention_mask"]
        )
        input_dict = {"input_ids": input_ids, "attention_mask": attention_mask}
    else:
        input_dict = {"input_ids": tokenized_data["input_ids"], "attention_mask": tokenized_data["attention_mask"]}
        sorting_indices = None

    return input_dict, sorting_indices


def _get_progress_bar(dataloader: DataLoader, verbose: bool = False) -> Union[DataLoader, "tqdm.auto.tqdm"]:
    """Wrap dataloader in progressbar if asked for.

    Function will return either the dataloader itself when `verbose = False`, or it wraps the dataloader with
    `tqdm.auto.tqdm`, when `verbose = True` to display a progress bar during the embbeddings calculation.

    """
    import tqdm

    return tqdm.auto.tqdm(dataloader) if verbose else dataloader


def _check_shape_of_model_output(output: Tensor, input_ids: Tensor) -> None:
    """Check if the shape of the user's own model output."""
    bs, seq_len = input_ids.shape[:2]
    invalid_out_shape = len(output.shape) != 3 or output.shape[0] != bs or output.shape[1] != seq_len
    if invalid_out_shape:
        raise ValueError(
            "The model output must be `Tensor` of a shape `[batch_size, seq_len, model_dim]` "
            f"i.e. [{bs}, {seq_len}. , `model_dim`], but got {output.shape}."
        )


def _load_tokenizer_and_model(
    model_name_or_path: Union[str, os.PathLike], device: Optional[Union[str, torch.device]] = None
) -> tuple["PreTrainedTokenizerBase", "PreTrainedModel"]:
    """Load HuggingFace `transformers`' tokenizer and model. This function also handle a device placement.

    Args:
        model_name_or_path:
            A name or a model path used to load `transformers` pretrained model.
        device:
            A device to be used for calculation.

    Return:
        Initialized `transformers`' tokenizer and model.

    """
    from transformers import AutoModelForMaskedLM, AutoTokenizer

    tokenizer = AutoTokenizer.from_pretrained(model_name_or_path)
    model = AutoModelForMaskedLM.from_pretrained(model_name_or_path)
    model.eval()
    model.to(device)
    return tokenizer, model


class TextDataset(Dataset):
    """PyTorch dataset class for storing tokenized sentences and other properties used for BERT score calculation."""

    def __init__(
        self,
        text: list[str],
        tokenizer: Any,
        max_length: int = 512,
        preprocess_text_fn: Callable[
            [list[str], Any, int, bool], Union[dict[str, Tensor], tuple[dict[str, Tensor], Optional[Tensor]]]
        ] = _preprocess_text,
        idf: bool = False,
        tokens_idf: Optional[dict[int, float]] = None,
        truncation: bool = False,
    ) -> None:
        """Initialize text dataset class.

        Args:
            text: An iterable of sentences.
            tokenizer: `AutoTokenizer` instance from `transformers` package.
            max_length: A maximum sequence length.
            preprocess_text_fn: A function used for processing the input sentences.
            idf: An indication of whether calculate token inverse document frequencies to weight the model embeddings.
            tokens_idf: Inverse document frequencies (these should be calculated on reference sentences).
            truncation: An indication of whether tokenized sequences should be padded only to the length of the longest

        """
        _text = preprocess_text_fn(text, tokenizer, max_length, truncation)
        if isinstance(_text, tuple):
            self.text, self.sorting_indices = _text
        else:
            self.text = _text
        self.max_length = self.text["input_ids"].shape[1]
        self.num_sentences = len(text)
        self.idf = idf
        self.tokens_idf = {}
        if idf:
            self.tokens_idf = tokens_idf if tokens_idf is not None else self._get_tokens_idf()

    def __getitem__(self, idx: int) -> dict[str, Tensor]:
        """Get the input ids and attention mask belonging to a specific datapoint."""
        input_ids = self.text["input_ids"][idx, :]
        attention_mask = self.text["attention_mask"][idx, :]
        inputs_dict = {"input_ids": input_ids, "attention_mask": attention_mask}
        if self.idf:
            input_ids_idf = torch.tensor([self.tokens_idf[input_idx] for input_idx in input_ids.tolist()])
            inputs_dict["input_ids_idf"] = input_ids_idf
        return inputs_dict

    def __len__(self) -> int:
        """Return the number of sentences in the dataset."""
        return self.num_sentences

    def _get_tokens_idf(self) -> dict[int, float]:
        """Calculate token inverse document frequencies.

        Return:
            A python dictionary containing inverse document frequencies for token ids.

        """
        token_counter: Counter = Counter()
        for tokens in map(self._set_of_tokens, self.text["input_ids"]):
            token_counter.update(tokens)

        tokens_idf: dict[int, float] = defaultdict(self._get_tokens_idf_default_value)
        tokens_idf.update({
            idx: math.log((self.num_sentences + 1) / (occurrence + 1)) for idx, occurrence in token_counter.items()
        })
        return tokens_idf

    def _get_tokens_idf_default_value(self) -> float:
        """Ensure `defaultdict` can be pickled."""
        return math.log((self.num_sentences + 1) / 1)

    @staticmethod
    def _set_of_tokens(input_ids: Tensor) -> set:
        """Return set of tokens from the `input_ids` :class:`~torch.Tensor`."""
        return set(input_ids.tolist())


class TokenizedDataset(TextDataset):
    """The child class of `TextDataset` class used with already tokenized data."""

    def __init__(
        self,
        input_ids: Tensor,
        attention_mask: Tensor,
        idf: bool = False,
        tokens_idf: Optional[dict[int, float]] = None,
    ) -> None:
        """Initialize the dataset class.

        Args:
            input_ids: Input indexes
            attention_mask: Attention mask
            idf:
                An indication of whether calculate token inverse document frequencies to weight the model embeddings.
            tokens_idf: Inverse document frequencies (these should be calculated on reference sentences).

        """
        text = dict(
            zip(
                ["input_ids", "attention_mask", "sorting_indices"],
                _sort_data_according_length(input_ids, attention_mask),
            )
        )
        self.sorting_indices = text.pop("sorting_indices")
        self.text = _input_data_collator(text)
        self.num_sentences = len(self.text["input_ids"])
        self.max_length = self.text["input_ids"].shape[1]
        self.idf = idf
        self.tokens_idf = {}
        if idf:
            self.tokens_idf = tokens_idf if tokens_idf is not None else self._get_tokens_idf()
