Refactor subscription duration calculation in PanelWebhookService and SubscriptionService

- Introduced a utility function `add_months` to handle subscription duration calculations based on calendar months instead of a fixed 30-day period.
- Updated the auto-renewal logic in `PanelWebhookService` to use the new function for extending subscription end dates.
- Adjusted the duration calculation in `SubscriptionService` to derive the end date after a specified number of months, improving accuracy in subscription management.

bot/services/panel_webhook_service.py

@@ -11,6 +11,7 @@ from config.settings import Settings
 from bot.middlewares.i18n import JsonI18n
 from bot.keyboards.inline.user_keyboards import get_subscribe_only_markup
 from db.dal import user_dal
+from bot.utils.date_utils import add_months
 
 EVENT_MAP = {
     "user.expires_in_72_hours": (3, "subscription_72h_notification"),
@@ -48,7 +49,7 @@ class PanelWebhookService:
         Returns True if an auto-renewal was performed (and renewal message sent), False otherwise.
         """
         from db.dal import subscription_dal, payment_dal
-        from datetime import datetime, timezone, timedelta
+        from datetime import datetime, timezone
         
         try:
             auto_renewed = False
@@ -68,8 +69,8 @@ class PanelWebhookService:
                     # This user has tribute payments, auto-renew for the same duration
                     logging.info(f"Auto-renewing tribute subscription for user {user_id} for {last_tribute_duration} months")
                     
-                    # Extend subscription by the last payment duration
-                    new_end_date = datetime.now(timezone.utc) + timedelta(days=last_tribute_duration * 30)
+                    # Extend subscription by the last payment duration (calendar months)
+                    new_end_date = add_months(datetime.now(timezone.utc), last_tribute_duration)
                     
                     await subscription_dal.update_subscription(
                         session,

bot/services/subscription_service.py

@@ -6,6 +6,7 @@ from aiogram import Bot
 from bot.middlewares.i18n import JsonI18n
 
 from db.dal import user_dal, subscription_dal, promo_code_dal, payment_dal
+from bot.utils.date_utils import add_months
 from db.models import User, Subscription
 
 from config.settings import Settings
@@ -424,7 +425,9 @@ class SubscriptionService:
         ):
             start_date = current_active_sub.end_date
 
-        duration_days_total = months * 30
+        # base duration by months
+        end_after_months = add_months(start_date, months)
+        duration_days_total = (end_after_months - start_date).days
         applied_promo_bonus_days = 0
 
         if promo_code_id_from_payment:

bot/utils/date_utils.py

@@ -0,0 +1,27 @@
+from datetime import datetime, timedelta
+
+
+def add_months(base_dt: datetime, months_to_add: int) -> datetime:
+    """Add calendar months to a datetime, clamping the day to the month's length.
+
+    Preserves tzinfo from base_dt.
+    """
+    year = base_dt.year
+    month = base_dt.month + months_to_add
+    day = base_dt.day
+
+    # Normalize year and month
+    year += (month - 1) // 12
+    month = ((month - 1) % 12) + 1
+
+    # Determine last day of target month by rolling to next month's first day and subtracting 1 day
+    if month == 12:
+        next_month_first = datetime(year + 1, 1, 1, tzinfo=base_dt.tzinfo)
+    else:
+        next_month_first = datetime(year, month + 1, 1, tzinfo=base_dt.tzinfo)
+    last_day = (next_month_first - timedelta(days=1)).day
+
+    clamped_day = min(day, last_day)
+    return base_dt.replace(year=year, month=month, day=clamped_day)
+
+