Move slot expansion logic to ExchangeService

- Add get_available_slots() and _expand_availability_to_slots() to ExchangeService
- Update routes/exchange.py to use ExchangeService.get_available_slots()
- Remove all business logic from get_available_slots endpoint
- Add AvailabilityRepository to ExchangeService dependencies
- Add Availability and BookableSlot imports to ExchangeService
- Fix import path for validate_date_in_range (use date_validation module)
- Remove unused user_repo variable and import from routes/invites.py
- Fix mypy error in ValidationError by adding proper type annotation

backend/services/exchange.py

@@ -14,6 +14,7 @@ from exceptions import (
     ServiceUnavailableError,
 )
 from models import (
+    Availability,
     BitcoinTransferMethod,
     Exchange,
     ExchangeStatus,
@@ -21,8 +22,10 @@ from models import (
     TradeDirection,
     User,
 )
+from repositories.availability import AvailabilityRepository
 from repositories.exchange import ExchangeRepository
 from repositories.price import PriceRepository
+from schemas import AvailableSlotsResponse, BookableSlot
 from shared_constants import (
     EUR_TRADE_INCREMENT,
     EUR_TRADE_MAX,
@@ -44,6 +47,7 @@ class ExchangeService:
         self.db = db
         self.price_repo = PriceRepository(db)
         self.exchange_repo = ExchangeRepository(db)
+        self.availability_repo = AvailabilityRepository(db)
 
     def apply_premium_for_direction(
         self,
@@ -379,3 +383,73 @@ class ExchangeService:
         await self.db.refresh(exchange)
 
         return exchange
+
+    def _expand_availability_to_slots(
+        self, avail: Availability, slot_date: date, booked_starts: set[datetime]
+    ) -> list[BookableSlot]:
+        """
+        Expand an availability block into individual slots, filtering out booked ones.
+
+        Args:
+            avail: Availability record
+            slot_date: Date for the slots
+            booked_starts: Set of already-booked slot start times
+
+        Returns:
+            List of available BookableSlot records
+        """
+        slots: list[BookableSlot] = []
+
+        # Start from the availability's start time
+        current_start = datetime.combine(slot_date, avail.start_time, tzinfo=UTC)
+        avail_end = datetime.combine(slot_date, avail.end_time, tzinfo=UTC)
+
+        while current_start + timedelta(minutes=SLOT_DURATION_MINUTES) <= avail_end:
+            slot_end = current_start + timedelta(minutes=SLOT_DURATION_MINUTES)
+
+            # Only include if not already booked
+            if current_start not in booked_starts:
+                slots.append(BookableSlot(start_time=current_start, end_time=slot_end))
+
+            current_start = slot_end
+
+        return slots
+
+    async def get_available_slots(self, date_param: date) -> AvailableSlotsResponse:
+        """
+        Get available booking slots for a specific date.
+
+        Returns all slots that:
+        - Fall within admin-defined availability windows
+        - Are not already booked by another user
+
+        Args:
+            date_param: Date to get slots for
+
+        Returns:
+            AvailableSlotsResponse with date and list of available slots
+
+        Raises:
+            BadRequestError: If date is out of range
+        """
+        validate_date_in_range(date_param, context="book")
+
+        # Get availability for the date
+        availabilities = await self.availability_repo.get_by_date(date_param)
+
+        if not availabilities:
+            return AvailableSlotsResponse(date=date_param, slots=[])
+
+        # Get already booked slots for the date
+        booked_starts = await self.exchange_repo.get_booked_slots_for_date(date_param)
+
+        # Expand each availability into slots
+        all_slots: list[BookableSlot] = []
+        for avail in availabilities:
+            slots = self._expand_availability_to_slots(avail, date_param, booked_starts)
+            all_slots.extend(slots)
+
+        # Sort by start time
+        all_slots.sort(key=lambda s: s.start_time)
+
+        return AvailableSlotsResponse(date=date_param, slots=all_slots)