import re

from django.conf import settings
from django.core.exceptions import ValidationError
from django.db import models
from django.utils.translation import gettext_lazy as _
from django_tidb.fields import BigAutoRandomField


EXAM_VOUCHER_PATTERN = re.compile(r"^EXAM-[A-Z0-9]{5}(-[A-Z0-9]{5}){4}$")


def exam_voucher_code_validator(value: str) -> None:
    if not EXAM_VOUCHER_PATTERN.match(value):
        raise ValidationError(_("Invalid exam voucher code format"))


class ExamVoucher(models.Model):
    class UsedChoices(models.TextChoices):
        N = "N"
        Y = "Y"

    id = BigAutoRandomField(primary_key=True)
    unique_code = models.CharField(
        max_length=34,
        unique=True,
        validators=[exam_voucher_code_validator],
    )
    exam = models.ForeignKey("labs.Exam", on_delete=models.CASCADE)
    valid_before = models.DateField(null=True, blank=True)
    used = models.CharField(
        max_length=1, default=UsedChoices.N, choices=UsedChoices.choices
    )
    redeem_at = models.DateTimeField(null=True, blank=True)
    redeem_by = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.DO_NOTHING,
        null=True,
        blank=True,
    )
    marketing_code = models.CharField(max_length=100, blank=True, default="")
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    class Meta:
        db_table = "exam_vouchers"
        indexes = [
            models.Index(fields=["exam", "used"], name="idx_ev_exam_used"),
        ]