from __future__ import annotations
from pathlib import Path
import re
from datetime import date

DEFAULT_PATTERN = r"(?P<year>\d{4})-(?P<seq>\d{4})"

def suggest_next_invoice_number(invoices_root: Path, year: int | None = None, pattern: str = DEFAULT_PATTERN) -> str:
    invoices_root = invoices_root.expanduser().resolve()
    y = year or date.today().year
    rx = re.compile(pattern)

    max_seq = 0
    if invoices_root.exists():
        for d in invoices_root.iterdir():
            if not d.is_dir():
                continue
            m = rx.search(d.name)
            if not m:
                continue
            try:
                yr = int(m.group("year"))
                seq = int(m.group("seq"))
            except Exception:
                continue
            if yr == y and seq > max_seq:
                max_seq = seq
    return f"{y}-{max_seq+1:04d}"


from contextlib import contextmanager

@contextmanager
def invoice_root_lock(root: Path):
    """Serialize local number allocation and folder creation on Linux."""
    import fcntl
    root = root.expanduser().resolve()
    root.mkdir(parents=True, exist_ok=True)
    with (root / '.jr-einvoice.lock').open('a') as lock:
        fcntl.flock(lock, fcntl.LOCK_EX)
        try:
            yield
        finally:
            fcntl.flock(lock, fcntl.LOCK_UN)