"""Tiny disk cache for JSON over HTTP, keyed by URL, expiry by TTL seconds."""
import hashlib, json, time, urllib.error, urllib.request
from .config import CACHE_DIR

UA = "PuGa/0.1 (personal advisory toolkit)"


def get_json(url: str, ttl: int, headers: dict[str, str] | None = None, refresh: bool = False):
    CACHE_DIR.mkdir(parents=True, exist_ok=True)
    f = CACHE_DIR / (hashlib.sha1(url.encode()).hexdigest()[:16] + ".json")
    if not refresh and f.exists() and time.time() - f.stat().st_mtime < ttl:
        return json.loads(f.read_text())
    req = urllib.request.Request(url, headers={"User-Agent": UA, **(headers or {})})
    for attempt in range(4):                      # transient SSL/connection errors happen on long scans
        try:
            with urllib.request.urlopen(req, timeout=60) as r:
                data = json.load(r)
            break
        except (urllib.error.URLError, ConnectionError, TimeoutError):
            if attempt == 3:
                raise
            time.sleep(1.5 * (attempt + 1))
    f.write_text(json.dumps(data))
    return data