import base64

from cryptography.fernet import Fernet, MultiFernet, InvalidToken
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC
from django.conf import settings
from django.core import validators
from django.db import models
from django.db.backends.base.operations import BaseDatabaseOperations
from django.utils.functional import cached_property


class EncryptedFieldMixin(object):
    @cached_property
    def keys(self):
        keys = []
        salt_keys = (
            settings.SALT_KEY
            if isinstance(settings.SALT_KEY, list)
            else [settings.SALT_KEY]
        )
        for salt_key in salt_keys:
            salt = bytes(salt_key, "utf-8")
            kdf = PBKDF2HMAC(
                algorithm=hashes.SHA256(),
                length=32,
                salt=salt,
                iterations=100000,
                backend=default_backend(),
            )
            keys.append(
                base64.urlsafe_b64encode(
                    kdf.derive(settings.SECRET_KEY.encode("utf-8"))
                )
            )
        return keys

    @cached_property
    def f(self):
        if len(self.keys) == 1:
            return Fernet(self.keys[0])
        return MultiFernet([Fernet(k) for k in self.keys])

    def get_internal_type(self):
        """
        To treat everything as text
        """
        return "TextField"

    def get_prep_value(self, value):
        value = super().get_prep_value(value)
        if value:
            if not isinstance(value, str):
                value = str(value)
            return self.f.encrypt(bytes(value, "utf-8")).decode("utf-8")
        return None

    def get_db_prep_value(self, value, connection, prepared=False):
        if not prepared:
            value = self.get_prep_value(value)
        return value

    def from_db_value(self, value, expression, connection):
        return self.to_python(value)

    def to_python(self, value):
        if (
            value is None
            or not isinstance(value, str)
            or hasattr(self, "_already_decrypted")
        ):
            return value
        try:
            value = self.f.decrypt(bytes(value, "utf-8")).decode("utf-8")
        except InvalidToken:
            pass
        except UnicodeEncodeError:
            pass
        return super(EncryptedFieldMixin, self).to_python(value)

    def clean(self, value, model_instance):
        """
        Create and assign a semaphore so that to_python method will not try to decrypt an already decrypted value
        during cleaning of a form
        """
        self._already_decrypted = True
        ret = super().clean(value, model_instance)
        del self._already_decrypted
        return ret


class EncryptedCharField(EncryptedFieldMixin, models.CharField):
    pass


class EncryptedTextField(EncryptedFieldMixin, models.TextField):
    pass


class EncryptedDateTimeField(EncryptedFieldMixin, models.DateTimeField):
    pass


class EncryptedIntegerField(EncryptedFieldMixin, models.IntegerField):
    @cached_property
    def validators(self):
        # These validators can't be added at field initialization time since
        # they're based on values retrieved from `connection`.
        validators_ = [*self.default_validators, *self._validators]
        internal_type = models.IntegerField().get_internal_type()
        min_value, max_value = BaseDatabaseOperations.integer_field_ranges[internal_type]
        if min_value is not None and not any(
            (
                isinstance(validator, validators.MinValueValidator)
                and (
                    validator.limit_value()
                    if callable(validator.limit_value)
                    else validator.limit_value
                )
                >= min_value
            )
            for validator in validators_
        ):
            validators_.append(validators.MinValueValidator(min_value))
        if max_value is not None and not any(
            (
                isinstance(validator, validators.MaxValueValidator)
                and (
                    validator.limit_value()
                    if callable(validator.limit_value)
                    else validator.limit_value
                )
                <= max_value
            )
            for validator in validators_
        ):
            validators_.append(validators.MaxValueValidator(max_value))
        return validators_


class EncryptedDateField(EncryptedFieldMixin, models.DateField):
    pass


class EncryptedFloatField(EncryptedFieldMixin, models.FloatField):
    pass


class EncryptedEmailField(EncryptedFieldMixin, models.EmailField):
    pass


class EncryptedBooleanField(EncryptedFieldMixin, models.BooleanField):
    pass