"""
cache.py — Tracks already-processed file IDs to avoid redownloading.
Persists to a simple JSON file on disk.
"""

import json
import logging
from pathlib import Path

log = logging.getLogger(__name__)

CACHE_FILE = Path("./data/cache.json")


def _load() -> set:
    if not CACHE_FILE.exists():
        return set()
    try:
        with open(CACHE_FILE, "r") as f:
            return set(json.load(f))
    except Exception:
        return set()


def _save(seen: set) -> None:
    with open(CACHE_FILE, "w") as f:
        json.dump(list(seen), f)


def is_seen(file_id: int) -> bool:
    return file_id in _load()


def mark_seen(file_id: int) -> None:
    seen = _load()
    seen.add(file_id)
    _save(seen)
    log.debug(f"  Cached file ID {file_id}")