from __future__ import annotations

import copy
import logging
from abc import ABC, abstractmethod
from dataclasses import dataclass
from enum import Enum
from typing import (
    TYPE_CHECKING,
    Any,
    Callable,
    Literal,
    Optional,
    TypeVar,
    Union,
)

from langchain_core.documents import BaseDocumentTransformer, Document
from typing_extensions import Self

if TYPE_CHECKING:
    from collections.abc import Collection, Iterable, Sequence
    from collections.abc import Set as AbstractSet

logger = logging.getLogger(__name__)

TS = TypeVar("TS", bound="TextSplitter")


class TextSplitter(BaseDocumentTransformer, ABC):
    """Interface for splitting text into chunks."""

    def __init__(
        self,
        chunk_size: int = 4000,
        chunk_overlap: int = 200,
        length_function: Callable[[str], int] = len,
        keep_separator: Union[bool, Literal["start", "end"]] = False,  # noqa: FBT001,FBT002
        add_start_index: bool = False,  # noqa: FBT001,FBT002
        strip_whitespace: bool = True,  # noqa: FBT001,FBT002
    ) -> None:
        """Create a new TextSplitter.

        Args:
            chunk_size: Maximum size of chunks to return
            chunk_overlap: Overlap in characters between chunks
            length_function: Function that measures the length of given chunks
            keep_separator: Whether to keep the separator and where to place it
                            in each corresponding chunk (True='start')
            add_start_index: If `True`, includes chunk's start index in metadata
            strip_whitespace: If `True`, strips whitespace from the start and end of
                              every document
        """
        if chunk_size <= 0:
            msg = f"chunk_size must be > 0, got {chunk_size}"
            raise ValueError(msg)
        if chunk_overlap < 0:
            msg = f"chunk_overlap must be >= 0, got {chunk_overlap}"
            raise ValueError(msg)
        if chunk_overlap > chunk_size:
            msg = (
                f"Got a larger chunk overlap ({chunk_overlap}) than chunk size "
                f"({chunk_size}), should be smaller."
            )
            raise ValueError(msg)
        self._chunk_size = chunk_size
        self._chunk_overlap = chunk_overlap
        self._length_function = length_function
        self._keep_separator = keep_separator
        self._add_start_index = add_start_index
        self._strip_whitespace = strip_whitespace

    @abstractmethod
    def split_text(self, text: str) -> list[str]:
        """Split text into multiple components."""

    def create_documents(
        self, texts: list[str], metadatas: Optional[list[dict[Any, Any]]] = None
    ) -> list[Document]:
        """Create documents from a list of texts."""
        _metadatas = metadatas or [{}] * len(texts)
        documents = []
        for i, text in enumerate(texts):
            index = 0
            previous_chunk_len = 0
            for chunk in self.split_text(text):
                metadata = copy.deepcopy(_metadatas[i])
                if self._add_start_index:
                    offset = index + previous_chunk_len - self._chunk_overlap
                    index = text.find(chunk, max(0, offset))
                    metadata["start_index"] = index
                    previous_chunk_len = len(chunk)
                new_doc = Document(page_content=chunk, metadata=metadata)
                documents.append(new_doc)
        return documents

    def split_documents(self, documents: Iterable[Document]) -> list[Document]:
        """Split documents."""
        texts, metadatas = [], []
        for doc in documents:
            texts.append(doc.page_content)
            metadatas.append(doc.metadata)
        return self.create_documents(texts, metadatas=metadatas)

    def _join_docs(self, docs: list[str], separator: str) -> Optional[str]:
        text = separator.join(docs)
        if self._strip_whitespace:
            text = text.strip()
        if text == "":
            return None
        return text

    def _merge_splits(self, splits: Iterable[str], separator: str) -> list[str]:
        # We now want to combine these smaller pieces into medium size
        # chunks to send to the LLM.
        separator_len = self._length_function(separator)

        docs = []
        current_doc: list[str] = []
        total = 0
        for d in splits:
            _len = self._length_function(d)
            if (
                total + _len + (separator_len if len(current_doc) > 0 else 0)
                > self._chunk_size
            ):
                if total > self._chunk_size:
                    logger.warning(
                        f"Created a chunk of size {total}, "
                        f"which is longer than the specified {self._chunk_size}"
                    )
                if len(current_doc) > 0:
                    doc = self._join_docs(current_doc, separator)
                    if doc is not None:
                        docs.append(doc)
                    # Keep on popping if:
                    # - we have a larger chunk than in the chunk overlap
                    # - or if we still have any chunks and the length is long
                    while total > self._chunk_overlap or (
                        total + _len + (separator_len if len(current_doc) > 0 else 0)
                        > self._chunk_size
                        and total > 0
                    ):
                        total -= self._length_function(current_doc[0]) + (
                            separator_len if len(current_doc) > 1 else 0
                        )
                        current_doc = current_doc[1:]
            current_doc.append(d)
            total += _len + (separator_len if len(current_doc) > 1 else 0)
        doc = self._join_docs(current_doc, separator)
        if doc is not None:
            docs.append(doc)
        return docs

    @classmethod
    def from_huggingface_tokenizer(cls, tokenizer: Any, **kwargs: Any) -> TextSplitter:
        """Text splitter that uses HuggingFace tokenizer to count length."""
        try:
            from transformers.tokenization_utils_base import PreTrainedTokenizerBase

            if not isinstance(tokenizer, PreTrainedTokenizerBase):
                msg = (
                    "Tokenizer received was not an instance of PreTrainedTokenizerBase"
                )
                raise ValueError(msg)

            def _huggingface_tokenizer_length(text: str) -> int:
                return len(tokenizer.tokenize(text))

        except ImportError as err:
            msg = (
                "Could not import transformers python package. "
                "Please install it with `pip install transformers`."
            )
            raise ValueError(msg) from err
        return cls(length_function=_huggingface_tokenizer_length, **kwargs)

    @classmethod
    def from_tiktoken_encoder(
        cls,
        encoding_name: str = "gpt2",
        model_name: Optional[str] = None,
        allowed_special: Union[Literal["all"], AbstractSet[str]] = set(),
        disallowed_special: Union[Literal["all"], Collection[str]] = "all",
        **kwargs: Any,
    ) -> Self:
        """Text splitter that uses tiktoken encoder to count length."""
        try:
            import tiktoken
        except ImportError as err:
            msg = (
                "Could not import tiktoken python package. "
                "This is needed in order to calculate max_tokens_for_prompt. "
                "Please install it with `pip install tiktoken`."
            )
            raise ImportError(msg) from err

        if model_name is not None:
            enc = tiktoken.encoding_for_model(model_name)
        else:
            enc = tiktoken.get_encoding(encoding_name)

        def _tiktoken_encoder(text: str) -> int:
            return len(
                enc.encode(
                    text,
                    allowed_special=allowed_special,
                    disallowed_special=disallowed_special,
                )
            )

        if issubclass(cls, TokenTextSplitter):
            extra_kwargs = {
                "encoding_name": encoding_name,
                "model_name": model_name,
                "allowed_special": allowed_special,
                "disallowed_special": disallowed_special,
            }
            kwargs = {**kwargs, **extra_kwargs}

        return cls(length_function=_tiktoken_encoder, **kwargs)

    def transform_documents(
        self, documents: Sequence[Document], **kwargs: Any
    ) -> Sequence[Document]:
        """Transform sequence of documents by splitting them."""
        return self.split_documents(list(documents))


class TokenTextSplitter(TextSplitter):
    """Splitting text to tokens using model tokenizer."""

    def __init__(
        self,
        encoding_name: str = "gpt2",
        model_name: Optional[str] = None,
        allowed_special: Union[Literal["all"], AbstractSet[str]] = set(),
        disallowed_special: Union[Literal["all"], Collection[str]] = "all",
        **kwargs: Any,
    ) -> None:
        """Create a new TextSplitter."""
        super().__init__(**kwargs)
        try:
            import tiktoken
        except ImportError as err:
            msg = (
                "Could not import tiktoken python package. "
                "This is needed in order to for TokenTextSplitter. "
                "Please install it with `pip install tiktoken`."
            )
            raise ImportError(msg) from err

        if model_name is not None:
            enc = tiktoken.encoding_for_model(model_name)
        else:
            enc = tiktoken.get_encoding(encoding_name)
        self._tokenizer = enc
        self._allowed_special = allowed_special
        self._disallowed_special = disallowed_special

    def split_text(self, text: str) -> list[str]:
        """Splits the input text into smaller chunks based on tokenization.

        This method uses a custom tokenizer configuration to encode the input text
        into tokens, processes the tokens in chunks of a specified size with overlap,
        and decodes them back into text chunks. The splitting is performed using the
        `split_text_on_tokens` function.

        Args:
            text (str): The input text to be split into smaller chunks.

        Returns:
            List[str]: A list of text chunks, where each chunk is derived from a portion
            of the input text based on the tokenization and chunking rules.
        """

        def _encode(_text: str) -> list[int]:
            return self._tokenizer.encode(
                _text,
                allowed_special=self._allowed_special,
                disallowed_special=self._disallowed_special,
            )

        tokenizer = Tokenizer(
            chunk_overlap=self._chunk_overlap,
            tokens_per_chunk=self._chunk_size,
            decode=self._tokenizer.decode,
            encode=_encode,
        )

        return split_text_on_tokens(text=text, tokenizer=tokenizer)


class Language(str, Enum):
    """Enum of the programming languages."""

    CPP = "cpp"
    GO = "go"
    JAVA = "java"
    KOTLIN = "kotlin"
    JS = "js"
    TS = "ts"
    PHP = "php"
    PROTO = "proto"
    PYTHON = "python"
    RST = "rst"
    RUBY = "ruby"
    RUST = "rust"
    SCALA = "scala"
    SWIFT = "swift"
    MARKDOWN = "markdown"
    LATEX = "latex"
    HTML = "html"
    SOL = "sol"
    CSHARP = "csharp"
    COBOL = "cobol"
    C = "c"
    LUA = "lua"
    PERL = "perl"
    HASKELL = "haskell"
    ELIXIR = "elixir"
    POWERSHELL = "powershell"
    VISUALBASIC6 = "visualbasic6"


@dataclass(frozen=True)
class Tokenizer:
    """Tokenizer data class."""

    chunk_overlap: int
    """Overlap in tokens between chunks"""
    tokens_per_chunk: int
    """Maximum number of tokens per chunk"""
    decode: Callable[[list[int]], str]
    """ Function to decode a list of token ids to a string"""
    encode: Callable[[str], list[int]]
    """ Function to encode a string to a list of token ids"""


def split_text_on_tokens(*, text: str, tokenizer: Tokenizer) -> list[str]:
    """Split incoming text and return chunks using tokenizer."""
    splits: list[str] = []
    input_ids = tokenizer.encode(text)
    start_idx = 0
    cur_idx = min(start_idx + tokenizer.tokens_per_chunk, len(input_ids))
    chunk_ids = input_ids[start_idx:cur_idx]
    while start_idx < len(input_ids):
        splits.append(tokenizer.decode(chunk_ids))
        if cur_idx == len(input_ids):
            break
        start_idx += tokenizer.tokens_per_chunk - tokenizer.chunk_overlap
        cur_idx = min(start_idx + tokenizer.tokens_per_chunk, len(input_ids))
        chunk_ids = input_ids[start_idx:cur_idx]
    return splits
