import hashlib, json
from datetime import datetime, timezone

def now() -> str:
    return datetime.now(timezone.utc).isoformat()

def digest(value: bytes | str) -> str:
    return hashlib.sha256(value if isinstance(value, bytes) else value.encode()).hexdigest()

def stable_id(tenant: str, source: str, item: str) -> str:
    return digest(f"{tenant}:{source}:{item}")[:32]

def require_scope(scope: dict, keys: tuple[str, ...]) -> None:
    if any(not scope.get(key) for key in keys):
        raise ValueError(f"missing required scope: {', '.join(keys)}")

def json_headers(token: str) -> dict[str, str]:
    return {"Authorization": f"Bearer {token}", "Accept": "application/json"}