"""Strict-size rolling local cache for certificate PDFs."""

from __future__ import annotations

import re
from pathlib import Path


class PdfCache:
    def __init__(self, root: str | Path, max_bytes: int) -> None:
        self.root = Path(root)
        self.max_bytes = int(max_bytes)
        self.root.mkdir(parents=True, exist_ok=True)

    # Parallel parse workers share one cache directory, so any file listed here may be gone by
    # the time it is stat()ed or unlinked: a vanished file counts as zero bytes, never an error.
    @staticmethod
    def _stat(path: Path):
        try:
            return path.stat()
        except FileNotFoundError:
            return None

    def size_bytes(self) -> int:
        return sum(
            stat.st_size
            for stat in (self._stat(p) for p in self.root.rglob("*") if p.is_file())
            if stat is not None
        )

    def _files_oldest_first(self) -> list[Path]:
        stamped = [
            (stat.st_mtime, p)
            for p in self.root.rglob("*")
            if p.is_file() and (stat := self._stat(p)) is not None
        ]
        return [p for _mtime, p in sorted(stamped, key=lambda item: item[0])]

    def safe_name(self, name: str) -> str:
        cleaned = re.sub(r"[^A-Za-z0-9_.-]", "_", str(name or "certificate.pdf"))
        return cleaned if cleaned.lower().endswith(".pdf") else f"{cleaned}.pdf"

    def write(self, name: str, data: bytes) -> Path:
        if len(data) > self.max_bytes:
            raise RuntimeError("PDF cache cap exceeded")

        for stale in self._files_oldest_first():
            if self.size_bytes() + len(data) <= self.max_bytes:
                break
            stale.unlink(missing_ok=True)

        if self.size_bytes() + len(data) > self.max_bytes:
            raise RuntimeError("PDF cache cap exceeded")

        path = self.root / self.safe_name(name)
        path.write_bytes(data)
        return path

    def delete(self, path: str | Path) -> None:
        p = Path(path)
        try:
            if p.is_file() and p.resolve().is_relative_to(self.root.resolve()):
                p.unlink()
        except FileNotFoundError:
            return