from __future__ import annotations

import calendar
from datetime import UTC, date, datetime
from zoneinfo import ZoneInfo

from flask import current_app


MONTH_NAMES = [
    "",
    "Januar",
    "Februar",
    "März",
    "April",
    "Mai",
    "Juni",
    "Juli",
    "August",
    "September",
    "Oktober",
    "November",
    "Dezember",
]


def get_timezone() -> ZoneInfo:
    return ZoneInfo(current_app.config["APP_TIMEZONE"])


def local_now() -> datetime:
    return datetime.now(UTC).astimezone(get_timezone())


def today_local() -> date:
    return local_now().date()


def previous_month(year: int, month: int) -> tuple[int, int]:
    if month == 1:
        return year - 1, 12
    return year, month - 1


def next_month(year: int, month: int) -> tuple[int, int]:
    if month == 12:
        return year + 1, 1
    return year, month + 1


def month_label(year: int, month: int) -> str:
    return f"{MONTH_NAMES[month]} {year}"


def add_months(base_date: date, months: int) -> date:
    month_index = base_date.month - 1 + months
    year = base_date.year + month_index // 12
    month = month_index % 12 + 1
    day = min(base_date.day, calendar.monthrange(year, month)[1])
    return date(year, month, day)


def month_bounds(year: int, month: int) -> tuple[datetime, datetime]:
    start = datetime(year, month, 1)
    next_year, next_month_value = next_month(year, month)
    end = datetime(next_year, next_month_value, 1)
    return start, end