first commit

app/services/dates.py

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+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
+