"""Safe text extraction for the supported import formats."""

from __future__ import annotations

from io import BytesIO
from pathlib import Path
from zipfile import ZipFile

from docx import Document
from pypdf import PdfReader


class ImportExtractionError(ValueError):
    pass


# A docx is a zip: a tiny compressed upload can expand into huge XML and burn
# minutes of parser CPU (measured: 90 KB -> ~30 MB -> 86 s, ~3 s per MB). A real
# resume decompresses to well under 1 MB, so 10 MB is generous and still bounds
# worst-case parse time to seconds.
_MAX_DECOMPRESSED_BYTES = 10 * 1024 * 1024


def _reject_decompression_bomb(content: bytes) -> None:
    try:
        with ZipFile(BytesIO(content)) as archive:
            total = sum(info.file_size for info in archive.infolist())
    except Exception as exc:
        raise ImportExtractionError("invalid_import_file") from exc
    if total > _MAX_DECOMPRESSED_BYTES:
        raise ImportExtractionError("import_file_too_large")


def normalize_upload_name(file_name: str) -> tuple[str, str]:
    safe_name = Path(file_name or "upload").name
    if not safe_name or safe_name in {".", ".."}:
        raise ImportExtractionError("invalid_file_name")
    extension = Path(safe_name).suffix.lower()
    if extension == ".doc":
        raise ImportExtractionError("legacy_doc_unsupported")
    if extension not in {".pdf", ".docx"}:
        raise ImportExtractionError("unsupported_import_format")
    return safe_name, extension


def validate_upload(*, extension: str, declared_mime: str | None, content: bytes) -> str:
    if not content:
        raise ImportExtractionError("empty_import_file")
    if extension == ".pdf":
        if not content.startswith(b"%PDF-"):
            raise ImportExtractionError("invalid_import_file")
        return "application/pdf"
    if not content.startswith(b"PK"):
        raise ImportExtractionError("invalid_import_file")
    if declared_mime and declared_mime not in {
        "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
        "application/octet-stream",
    }:
        raise ImportExtractionError("invalid_import_mime")
    return "application/vnd.openxmlformats-officedocument.wordprocessingml.document"


def extract_text(*, extension: str, content: bytes) -> str:
    if extension == ".pdf":
        try:
            reader = PdfReader(BytesIO(content))
            text = "\n".join(page.extract_text() or "" for page in reader.pages).strip()
        except Exception as exc:
            raise ImportExtractionError("ocr_required") from exc
        if not text:
            raise ImportExtractionError("ocr_required")
        return text
    _reject_decompression_bomb(content)
    try:
        document = Document(BytesIO(content))
    except Exception as exc:
        raise ImportExtractionError("invalid_import_file") from exc
    parts = [paragraph.text.strip() for paragraph in document.paragraphs if paragraph.text.strip()]
    for table in document.tables:
        for row in table.rows:
            values = [cell.text.strip() for cell in row.cells if cell.text.strip()]
            if values:
                parts.append(" | ".join(values))
    text = "\n".join(parts).strip()
    if not text:
        raise ImportExtractionError("empty_import_text")
    return text