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 = base64.b64encode(private.to_string()).decode()
            public_key_str = base64.b64encode(public.to_string()).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_string(base64.b64decode(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')

    def has_primary(self):
        return self.filter(primary=True).exists()


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_string(base64.b64decode(
            self.private_key.encode()))
        signature_byte = private.sign_deterministic(string.encode())
        return base64.b64encode(signature_byte).decode()