"""Utility functions"""

from base64 import b64decode, b64encode
import os

from nacl.signing import SigningKey
import yaml


class ConfigException(Exception):
    """Exception to raise if there is a problem with the configuration data"""


def tag(key):
    """Create tag from public key."""

    return b"@" + b64encode(bytes(key)) + b".ed25519"


def load_ssb_secret():
    """Load SSB keys from ~/.ssb"""

    with open(os.path.expanduser("~/.ssb/secret"), encoding="utf-8") as f:
        config = yaml.load(f, Loader=yaml.SafeLoader)

    if config["curve"] != "ed25519":
        raise ConfigException("Algorithm not known: " + config["curve"])

    server_prv_key = b64decode(config["private"][:-8])
    return {"keypair": SigningKey(server_prv_key[:32]), "id": config["id"]}