import io
from dataclasses import dataclass

import fitz  # pymupdf
from docx import Document


SUPPORTED_TYPES = {"pdf", "md", "docx", "xlsx"}


class UnsupportedFileType(Exception):
    pass


@dataclass(frozen=True)
class ExtractedPage:
    page: int
    text: str


def extract(data: bytes, file_type: str, filename: str) -> list[ExtractedPage]:
    file_type = file_type.lower().lstrip(".")
    if file_type not in SUPPORTED_TYPES:
        raise UnsupportedFileType(file_type)

    if file_type == "pdf":
        return _extract_pdf(data)
    if file_type == "md":
        return _extract_md(data)
    if file_type == "docx":
        return _extract_docx(data)
    if file_type == "xlsx":
        return [ExtractedPage(page=1, text=f"Tabelle: {filename}")]

    raise UnsupportedFileType(file_type)  # unreachable


def _extract_pdf(data: bytes) -> list[ExtractedPage]:
    pages: list[ExtractedPage] = []
    with fitz.open(stream=data, filetype="pdf") as doc:
        for i, page in enumerate(doc, start=1):
            pages.append(ExtractedPage(page=i, text=page.get_text() or ""))
    return pages


def _extract_md(data: bytes) -> list[ExtractedPage]:
    return [ExtractedPage(page=1, text=data.decode("utf-8", errors="replace"))]


def _extract_docx(data: bytes) -> list[ExtractedPage]:
    doc = Document(io.BytesIO(data))
    text = "\n\n".join(p.text for p in doc.paragraphs if p.text)
    return [ExtractedPage(page=1, text=text)]