"""Availability service for managing booking availability."""

from datetime import date

from sqlalchemy.ext.asyncio import AsyncSession

# Import for validation
from date_validation import validate_date_in_range
from exceptions import BadRequestError
from models import Availability
from repositories.availability import AvailabilityRepository
from schemas import AvailabilityDay, AvailabilityResponse, TimeSlot


class AvailabilityService:
    """Service for availability-related business logic."""

    def __init__(self, db: AsyncSession):
        self.db = db
        self.availability_repo = AvailabilityRepository(db)

    async def get_availability_for_range(
        self, from_date: date, to_date: date
    ) -> AvailabilityResponse:
        """
        Get availability slots for a date range, grouped by date.

        Args:
            from_date: Start date (inclusive)
            to_date: End date (inclusive)

        Returns:
            AvailabilityResponse with days grouped and sorted

        Raises:
            BadRequestError: If from_date > to_date
        """
        if from_date > to_date:
            raise BadRequestError("'from' date must be before or equal to 'to' date")

        # Query availability in range
        slots = await self.availability_repo.get_by_date_range(from_date, to_date)

        # Group by date
        days_dict: dict[date, list[TimeSlot]] = {}
        for slot in slots:
            if slot.date not in days_dict:
                days_dict[slot.date] = []
            days_dict[slot.date].append(
                TimeSlot(start_time=slot.start_time, end_time=slot.end_time)
            )

        # Convert to response format
        days = [
            AvailabilityDay(date=d, slots=days_dict[d])
            for d in sorted(days_dict.keys())
        ]

        return AvailabilityResponse(days=days)

    def _validate_slots(self, slots: list[TimeSlot]) -> None:
        """
        Validate that slots don't overlap and have valid time ordering.

        Raises:
            BadRequestError: If validation fails
        """
        # Validate slots don't overlap
        sorted_slots = sorted(slots, key=lambda s: s.start_time)
        for i in range(len(sorted_slots) - 1):
            if sorted_slots[i].end_time > sorted_slots[i + 1].start_time:
                end = sorted_slots[i].end_time
                start = sorted_slots[i + 1].start_time
                raise BadRequestError(
                    f"Time slots overlap: slot ending at {end} "
                    f"overlaps with slot starting at {start}"
                )

        # Validate each slot's end_time > start_time
        for slot in slots:
            if slot.end_time <= slot.start_time:
                raise BadRequestError(
                    f"Invalid time slot: end time {slot.end_time} "
                    f"must be after start time {slot.start_time}"
                )

    async def set_availability_for_date(
        self, target_date: date, slots: list[TimeSlot]
    ) -> AvailabilityDay:
        """
        Set availability for a specific date. Replaces any existing availability.

        Args:
            target_date: Date to set availability for
            slots: List of time slots for the date

        Returns:
            AvailabilityDay with the set slots

        Raises:
            BadRequestError: If date is invalid or slots are invalid
        """
        validate_date_in_range(target_date, context="set availability")

        # Validate slots
        self._validate_slots(slots)

        # Delete existing availability for this date
        await self.availability_repo.delete_by_date(target_date)

        # Create new availability slots
        availabilities = [
            Availability(
                date=target_date,
                start_time=slot.start_time,
                end_time=slot.end_time,
            )
            for slot in slots
        ]
        await self.availability_repo.create_multiple(availabilities)
        await self.availability_repo.commit()

        return AvailabilityDay(date=target_date, slots=slots)

    async def copy_availability(
        self, source_date: date, target_dates: list[date]
    ) -> AvailabilityResponse:
        """
        Copy availability from one day to multiple target days.

        Args:
            source_date: Date to copy availability from
            target_dates: List of dates to copy availability to

        Returns:
            AvailabilityResponse with copied days

        Raises:
            BadRequestError: If source date has no availability or dates are invalid
        """
        # Validate source date is in range
        validate_date_in_range(source_date, context="copy from")

        # Validate target dates
        for target_date in target_dates:
            validate_date_in_range(target_date, context="copy to")

        # Get source availability
        source_slots = await self.availability_repo.get_by_date(source_date)

        if not source_slots:
            raise BadRequestError(
                f"No availability found for source date {source_date}"
            )

        # Copy to each target date within a single atomic transaction
        # All deletes and inserts happen before commit, ensuring atomicity
        copied_days: list[AvailabilityDay] = []
        try:
            for target_date in target_dates:
                if target_date == source_date:
                    continue  # Skip copying to self

                # Delete existing availability for target date
                await self.availability_repo.delete_by_date(target_date)

                # Copy slots
                target_slots: list[TimeSlot] = []
                new_availabilities = [
                    Availability(
                        date=target_date,
                        start_time=source_slot.start_time,
                        end_time=source_slot.end_time,
                    )
                    for source_slot in source_slots
                ]
                await self.availability_repo.create_multiple(new_availabilities)
                target_slots = [
                    TimeSlot(
                        start_time=slot.start_time,
                        end_time=slot.end_time,
                    )
                    for slot in source_slots
                ]

                copied_days.append(
                    AvailabilityDay(date=target_date, slots=target_slots)
                )

            # Commit all changes atomically
            await self.availability_repo.commit()
        except Exception:
            # Rollback on any error to maintain atomicity
            await self.db.rollback()
            raise

        return AvailabilityResponse(days=copied_days)