import os.path
from sys import exit

from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import ec


# Simple tool to generate an ECDSA private key using the secp256k1 curve and save private and public keys
# as signing_key_priv.pem and signing_key_pub.pem

FILE_NAME_PRIV = 'signing_key_priv.pem'
FILE_NAME_PUB = 'signing_key_pub.pem'


def save_sk(sk, filename):
    pem = sk.private_bytes(
        encoding=serialization.Encoding.PEM,
        format=serialization.PrivateFormat.TraditionalOpenSSL,
        encryption_algorithm=serialization.NoEncryption()
    )
    with open(filename, 'wb') as pem_out:
        pem_out.write(pem)


def save_pk(pk, filename):
    pem = pk.public_bytes(
        encoding=serialization.Encoding.PEM,
        format=serialization.PublicFormat.SubjectPublicKeyInfo
    )
    with open(filename, 'wb') as pem_out:
        pem_out.write(pem)


if __name__ == '__main__':
    if os.path.exists(FILE_NAME_PRIV):
        print("A key with name \"{}\" already exists. Aborting.".format(FILE_NAME_PRIV))
        exit(1)

    sk = ec.generate_private_key(
        ec.SECP256K1, default_backend()
    )
    pk = sk.public_key()

    save_sk(sk, FILE_NAME_PRIV)
    save_pk(pk, FILE_NAME_PUB)
    print("Saved private key \"{}\" and public key \"{}\".".format(FILE_NAME_PRIV, FILE_NAME_PUB))