import calendar
import datetime
import re

from constance import config
from django.db import models
from django.utils import timezone
from django.utils.translation import gettext_lazy as _
from rules import is_superuser
from rules.contrib.models import RulesModel


class Season(RulesModel):
    start_date = models.DateField(_("start date"))
    end_date = models.DateField(_("end date"))

    class Meta:
        verbose_name = _("season")
        verbose_name_plural = _("seasons")
        ordering = ["start_date"]
        rules_permissions = {"add": is_superuser, "view": is_superuser, "change": is_superuser, "delete": is_superuser}
        constraints = [
            models.UniqueConstraint(fields=["start_date", "end_date"], name="season_start_date_end_date_unique", violation_error_message=_("Start and end date for a given season must be unique")),
            models.CheckConstraint(condition=models.Q(start_date__lt=models.F("end_date")), name="season_start_date_lt_end_date", violation_error_message=_("Start date must be before end date.")),
        ]

    def __str__(self):
        return _("Season '{start_date} - '{end_date}").format(start_date=self.start_date.strftime("%y"), end_date=self.end_date.strftime("%y"))

    @property
    def is_current(self) -> bool:
        return self.start_date <= timezone.now().date() <= self.end_date

    @property
    def date_range(self) -> tuple[datetime.date, datetime.date]:
        return self.start_date, self.end_date

    @classmethod
    def for_date(cls, current_date: datetime.date | None = None, values_only: bool = False) -> "tuple[datetime.date, datetime.date] | Season":
        if current_date is None:
            current_date = timezone.now().date()

        season = cls.objects.get(start_date__lte=current_date, end_date__gte=current_date)

        if values_only:
            return season.date_range
        return season

    @classmethod
    def generate_default(cls, day: int | None = None, month: int | None = None, duration: str | None = None) -> "Season":
        if day is None:
            day = config.TF_DEFAULT_SEASON_DAY
        if month is None:
            month = config.TF_DEFAULT_SEASON_MONTH
        if duration is None:
            duration = config.TF_DEFAULT_SEASON_DURATION

        current_year = timezone.now().date().year
        start_date = datetime.date(current_year, month, day)

        match = re.fullmatch(r"(\d+)([ym])", duration.strip().lower())
        if match is None:
            raise ValueError('Duration must be specified as "<number>y" or "<number>m", for example "1y", "1m", or "3m".')

        duration_value = int(match.group(1))
        duration_unit = match.group(2)

        if duration_unit == "y":
            end_date = cls._add_months(start_date, duration_value * 12) - datetime.timedelta(days=1)
        elif duration_unit == "m":
            end_date = cls._add_months(start_date, duration_value) - datetime.timedelta(days=1)
        else:
            raise ValueError('Duration unit must be "y" or "m".')

        return cls.objects.create(start_date=start_date, end_date=end_date)

    @staticmethod
    def _add_months(date_value: datetime.date, months: int) -> datetime.date:
        month_index = date_value.month - 1 + months
        year = date_value.year + month_index // 12
        month = month_index % 12 + 1
        day = min(date_value.day, calendar.monthrange(year, month)[1])

        return date_value.replace(year=year, month=month, day=day)