# utils/cache.py

Tracks already-processed Telegram document IDs to avoid redownloading.  
Persists to `data/cache.json` as a JSON array of integers.

## Public API

```python
from utils.cache import is_seen, mark_seen
```

### `is_seen(file_id: int) -> bool`
Returns `True` if this document ID has been processed before.  
Loads from disk on every call (safe for multi-process, slightly slow for hot loops — not an issue given download cadence).

### `mark_seen(file_id: int) -> None`
Adds `file_id` to the cache and persists to disk.

---

## Storage

- **File:** `data/cache.json`
- **Format:** JSON array of integers — `[123456789, 987654321, ...]`
- **No expiry** — grows indefinitely. Safe to delete to re-process all files.

---

## Notes

- `is_seen` + `mark_seen` are called in `core/scraper.py` after a successful download+process cycle, not before — so a file that fails mid-process will be retried on next run.
- Not thread-safe (load/modify/save is not atomic). Acceptable because downloads are sequential within the bot loop.