refactor: improve language normalization and date handling utilities

- Introduced a new `normalize_lang` function to standardize language codes across the application, ensuring consistent handling of user language preferences.
- Refactored date handling utilities by adding `parse_utc_iso` and `parse_utc_iso_naive` functions for better parsing of ISO 8601 date strings, enhancing timezone awareness.
- Updated various modules to utilize the new language normalization and date parsing functions, improving code clarity and maintainability.
- Enhanced error handling in date validation to raise specific `DateRangeValidationError` exceptions, providing clearer feedback on validation issues.
- Improved test coverage for date range validation and language normalization functionalities, ensuring robustness and reliability.

duty_teller/api/dependencies.py

@@ -10,15 +10,32 @@ from sqlalchemy.orm import Session
 import duty_teller.config as config
 from duty_teller.api.telegram_auth import validate_init_data_with_reason
 from duty_teller.db.repository import get_duties, get_user_by_telegram_id
-from duty_teller.db.schemas import DutyWithUser
+from duty_teller.db.schemas import DUTY_EVENT_TYPES, DutyWithUser
 from duty_teller.db.session import session_scope
 from duty_teller.i18n import t
-from duty_teller.utils.dates import validate_date_range
+from duty_teller.i18n.lang import normalize_lang
+from duty_teller.utils.dates import DateRangeValidationError, validate_date_range
 
 log = logging.getLogger(__name__)
 
-# First language tag from Accept-Language (e.g. "ru-RU,ru;q=0.9,en;q=0.8" -> "ru")
-_ACCEPT_LANG_TAG_RE = re.compile(r"^([a-zA-Z]{2,3})(?:-[a-zA-Z0-9]+)?\s*(?:;|,|$)")
+# Extract primary language code from first Accept-Language tag (e.g. "ru-RU" -> "ru").
+_ACCEPT_LANG_CODE_RE = re.compile(r"^([a-zA-Z]{2,3})(?:-|;|,|\s|$)")
+
+
+def _parse_first_language_code(header: str | None) -> str | None:
+    """Extract the first language code from Accept-Language header.
+
+    Args:
+        header: Raw Accept-Language value (e.g. "ru-RU,ru;q=0.9,en;q=0.8").
+
+    Returns:
+        Two- or three-letter code (e.g. 'ru', 'en') or None if missing/invalid.
+    """
+    if not header or not header.strip():
+        return None
+    first = header.strip().split(",")[0].strip()
+    m = _ACCEPT_LANG_CODE_RE.match(first)
+    return m.group(1).lower() if m else None
 
 
 def _lang_from_accept_language(header: str | None) -> str:
@@ -30,14 +47,8 @@ def _lang_from_accept_language(header: str | None) -> str:
     Returns:
         'ru' or 'en'.
     """
-    if not header or not header.strip():
-        return config.DEFAULT_LANGUAGE
-    first = header.strip().split(",")[0].strip()
-    m = _ACCEPT_LANG_TAG_RE.match(first)
-    if not m:
-        return "en"
-    code = m.group(1).lower()
-    return "ru" if code.startswith("ru") else "en"
+    code = _parse_first_language_code(header)
+    return normalize_lang(code if code is not None else config.DEFAULT_LANGUAGE)
 
 
 def _auth_error_detail(auth_reason: str, lang: str) -> str:
@@ -51,13 +62,12 @@ def _validate_duty_dates(from_date: str, to_date: str, lang: str) -> None:
     """Validate date range; raise HTTPException with translated detail."""
     try:
         validate_date_range(from_date, to_date)
+    except DateRangeValidationError as e:
+        key = "dates.bad_format" if e.kind == "bad_format" else "dates.from_after_to"
+        raise HTTPException(status_code=400, detail=t(lang, key)) from e
     except ValueError as e:
-        msg = str(e)
-        if "YYYY-MM-DD" in msg or "формате" in msg:
-            detail = t(lang, "dates.bad_format")
-        else:
-            detail = t(lang, "dates.from_after_to")
-        raise HTTPException(status_code=400, detail=detail) from e
+        # Backward compatibility if something else raises ValueError.
+        raise HTTPException(status_code=400, detail=t(lang, "dates.bad_format")) from e
 
 
 def get_validated_dates(
@@ -211,9 +221,7 @@ def fetch_duties_response(
             end_at=duty.end_at,
             full_name=full_name,
             event_type=(
-                duty.event_type
-                if duty.event_type in ("duty", "unavailable", "vacation")
-                else "duty"
+                duty.event_type if duty.event_type in DUTY_EVENT_TYPES else "duty"
             ),
         )
         for duty, full_name in rows