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 'pisa_sk.pem' 'and pisa_pk.pem', respectively.

SK_FILE_NAME = 'pisa_sk.pem'
PK_FILE_NAME = 'pisa_pk.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(SK_FILE_NAME):
        print("A key with name \"{}\" already exists. Aborting.".format(SK_FILE_NAME))
        exit(1)

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

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