import base64
from ecdsa import SigningKey, VerifyingKey, BadSignatureError
from django.db import models

TYPE_ECDSA = 'ecdsa'

APP_LABEL_BOARDS = 'boards'


class KeyPairManager(models.Manager):
    def generate_key(self, key_type=TYPE_ECDSA, primary=False):
        if primary and self.filter(primary=True).exists():
            raise Exception('There can be only one primary key')

        if key_type == TYPE_ECDSA:
            private = SigningKey.generate()
            public = private.get_verifying_key()

            private_key_str = private.to_pem().decode()
            public_key_str = public.to_pem().decode()

            return self.create(public_key=public_key_str,
                    private_key=private_key_str,
                    key_type=TYPE_ECDSA, primary=primary)
        else:
            raise Exception('Key type not supported')

    def verify(self, public_key_str, string, signature, key_type=TYPE_ECDSA):
        if key_type == TYPE_ECDSA:
            public = VerifyingKey.from_pem(public_key_str)
            signature_byte = base64.b64decode(signature)
            try:
                return public.verify(signature_byte, string.encode())
            except BadSignatureError:
                return False
        else:
            raise Exception('Key type not supported')


class KeyPair(models.Model):
    class Meta:
        app_label = APP_LABEL_BOARDS

    objects = KeyPairManager()

    public_key = models.TextField()
    private_key = models.TextField()
    key_type = models.TextField()
    primary = models.BooleanField(default=False)

    def __str__(self):
        return '%s: %s' % (self.key_type, self.public_key)

    def sign(self, string):
        private = SigningKey.from_pem(self.private_key)
        signature_byte = private.sign(string.encode())
        return base64.b64encode(signature_byte)