"""Read the first pages of a file to learn its text and page count. Sync: run in a thread."""
import html
import io
import logging
import os
import re
import zipfile
from dataclasses import dataclass
from typing import Optional

log = logging.getLogger(__name__)


@dataclass
class DocInfo:
    text: str = ""
    pages: Optional[int] = None


def _pdf(data: bytes) -> DocInfo:
    try:
        from pypdf import PdfReader
    except ImportError:
        return DocInfo()
    logging.getLogger("pypdf").setLevel(logging.ERROR)
    reader = PdfReader(io.BytesIO(data))
    pages = len(reader.pages)
    chunks = []
    for i in range(min(3, pages)):
        chunks.append(reader.pages[i].extract_text() or "")
    return DocInfo(text=" ".join(chunks), pages=pages)


def _pptx(data: bytes) -> DocInfo:
    with zipfile.ZipFile(io.BytesIO(data)) as z:
        slides = sorted(
            (n for n in z.namelist() if re.fullmatch(r"ppt/slides/slide\d+\.xml", n)),
            key=lambda n: int(re.findall(r"\d+", n)[0]),
        )
        chunks = []
        for name in slides[:3]:
            xml = z.read(name).decode("utf-8", "ignore")
            chunks.append(" ".join(html.unescape(t) for t in re.findall(r"<a:t>([^<]*)</a:t>", xml)))
    return DocInfo(text=" ".join(chunks), pages=len(slides))


def _docx(data: bytes) -> DocInfo:
    with zipfile.ZipFile(io.BytesIO(data)) as z:
        xml = z.read("word/document.xml").decode("utf-8", "ignore")
    text = " ".join(html.unescape(t) for t in re.findall(r"<w:t[^>]*>([^<]*)</w:t>", xml))
    return DocInfo(text=text)


def analyze(file_name: Optional[str], data: bytes) -> DocInfo:
    ext = os.path.splitext(file_name or "")[1].lower()
    try:
        if ext == ".pdf":
            info = _pdf(data)
        elif ext == ".pptx":
            info = _pptx(data)
        elif ext == ".docx":
            info = _docx(data)
        else:
            return DocInfo()
    except Exception as exc:  # encrypted / scanned / corrupt files must never break an upload
        log.info("Could not read %s: %r", file_name, exc)
        return DocInfo()
    info.text = re.sub(r"\s+", " ", info.text)[:6000]
    return info