"""PDF -> PDF passthrough (.pdf uploads).

A valid, unencrypted PDF is validated with pypdf and passed through to the
output with the standard naming/collision contract, re-stamping /Title from
the uploaded filename stem. It reuses common.finalize_pdf so the atomic
write path (.tmp + os.replace) and metadata handling are identical to every
other converter.

Rejections (all ValueError -> surfaced verbatim as a job error / CLI error):
  - corrupt / unparseable   -> "Invalid PDF: ... could not be parsed"
  - encrypted / password    -> "PDF rejected: ... encrypted or password-protected"
  - more than MAX_PAGES     -> "PDF too large: ... pages (max N)"
"""
from __future__ import annotations

import io
from pathlib import Path

from pypdf import PdfReader

from . import common

# req 1 (pdf passthrough): upper bound on page count for a pass-through PDF.
MAX_PAGES = 500


def convert(path: Path, job_id: str, progress_cb=None, output_dir=None,
            source_name=None) -> str:
    """Validate a PDF and pass it through to a same-named output PDF.

    Satisfies: req 1 (pdf passthrough — validate, stamp /Title, standard
    naming/collision, atomic write).
    """
    name = source_name or path.name
    stem = Path(name).stem or "book"
    raw = path.read_bytes()

    # req 1: validate with pypdf. Construction raises on header/body corruption.
    try:
        reader = PdfReader(io.BytesIO(raw))
    except Exception as exc:  # noqa: BLE001 - pypdf raises many corrupt-file types
        raise ValueError(f"Invalid PDF: {name} could not be parsed ({exc})") from exc

    # req 1: reject encrypted / password-protected BEFORE touching .pages
    # (accessing pages on an encrypted reader raises, not a clean error).
    if reader.is_encrypted:
        raise ValueError(f"PDF rejected: {name} is encrypted or password-protected")

    # req 1: count pages; a corrupt body beyond a valid header fails here.
    try:
        page_count = len(reader.pages)
    except Exception as exc:  # noqa: BLE001
        raise ValueError(f"Invalid PDF: {name} could not be parsed ({exc})") from exc

    # req 1: reject oversized documents (clear error, distinct from corrupt).
    if page_count > MAX_PAGES:
        raise ValueError(
            f"PDF too large: {name} has {page_count} pages (max {MAX_PAGES})"
        )

    # req 1: stamp /Title from the uploaded filename stem; standard naming/collision.
    common.report(progress_cb, 30.0, f"Passing through {name} (1/1)")
    out_dir = common.default_output_dir(output_dir)
    filename = common.derive_export_name(name, out_dir)
    return common.finalize_pdf(raw, out_dir, filename, job_id,
                               progress_cb=progress_cb, title=stem)