from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric import ec
from cryptography.hazmat.primitives.kdf.hkdf import HKDF
from cryptography.hazmat.primitives.serialization import PublicFormat, Encoding, load_pem_public_key

def generate_keys():
    private_key = ec.generate_private_key(
        ec.SECP384R1()
    )
    public_key = private_key.public_key()
    return public_key, private_key

def generate_shared_key(private_key:ec.EllipticCurvePrivateKey, public_key:ec.EllipticCurvePublicKey):
    shared_key = private_key.exchange(ec.ECDH(), public_key)
    return shared_key

def generate_derived_key(shared_key:bytes):
    derived_key = HKDF(
        algorithm=hashes.SHA256(),
        length=32,
        salt=None,
        info=None,
    ).derive(shared_key)
    return derived_key

def public_key_to_str(public_key:ec.EllipticCurvePublicKey, remove_header_and_footer=False):
    public_key_str = public_key.public_bytes(Encoding.PEM, PublicFormat.SubjectPublicKeyInfo).decode()
    if(remove_header_and_footer):
        public_key_str = public_key_str.replace('-----BEGIN PUBLIC KEY-----\n','')
        public_key_str = public_key_str.replace('\n-----END PUBLIC KEY-----\n','')
    return public_key_str

def load_public_key_str(public_key_str:str, removed_header_and_footer=False):
    if(removed_header_and_footer):
        public_key_str = f'-----BEGIN PUBLIC KEY-----\n{public_key_str}\n-----END PUBLIC KEY-----\n'
    return load_pem_public_key(public_key_str.encode())