import binascii

from gmssl import sm2


class ChisCryptoError(Exception):
    """Raised when CHIS crypto cannot encrypt a required field."""


def sm2_encrypt(public_key, raw_text):
    if not public_key:
        raise ChisCryptoError("CHIS public key is not configured")

    key = public_key
    if len(key) > 64 * 2:
        key = key[-64 * 2 :]

    try:
        text_bytes = str(raw_text).encode("utf-8")
        crypt_sm2 = sm2.CryptSM2(public_key=key, private_key="", mode=0)
        encrypted = crypt_sm2.encrypt(text_bytes)
        return "04" + binascii.hexlify(encrypted).decode("utf-8")
    except Exception as exc:
        raise ChisCryptoError("CHIS SM2 encryption failed") from exc