import uuid
import random
from datetime import timedelta

from django.utils import timezone
from django.db import models, transaction
from django.urls import reverse
from django.conf import settings


def generate_identifier():
    return uuid.uuid4().hex


def random_char_challenge():
    chars, ret = "abcdefghijklmnopqrstuvwxyz", ""
    for i in range(4):
        ret += random.choice(chars)
    return ret.upper(), ret



class CaptchaStore(models.Model):
    identifier = models.CharField(max_length=64, unique=True, default=generate_identifier)
    challenge = models.CharField(max_length=32)
    response = models.CharField(max_length=32)
    attempts = models.IntegerField(default=0)
    created_at = models.DateTimeField(auto_now_add=True)
    expires_at = models.DateTimeField()
    used_at = models.DateTimeField(null=True, blank=True)

    class Meta:
        db_table = 'pingcap_captcha_store'

    @classmethod
    def generate_challenge(cls) -> 'CaptchaStore':
        challenge, ret = random_char_challenge()
        store = cls.objects.create(
            challenge=challenge,
            response=ret,
            expires_at=timezone.now() + timedelta(minutes=10)
        )
        return store

    MAX_ATTEMPTS = 10

    @classmethod
    def verify(cls, key, response):
        try:
            with transaction.atomic():
                store = cls.objects.select_for_update().get(
                    identifier=key,
                    expires_at__gt=timezone.now(),
                    used_at__isnull=True,
                )
                if store.attempts >= cls.MAX_ATTEMPTS:
                    return False
                passed = response.lower() == store.response.lower()
                if passed:
                    store.used_at = timezone.now()
                store.attempts += 1
                store.save()
                return passed
        except cls.DoesNotExist:
            return False

    def to_frontend(self):
        return {
            "key": self.identifier,
            "image_url": f"{settings.SSO_PROVIDER_ENDPOINT}{reverse('captcha-image', args=[self.identifier])}",
        }