"""Calendar backend abstraction for Calendar TUI.

This module defines the abstract interface that all calendar backends must implement,
allowing the TUI to work with different calendar systems (khal, calcurse, etc.)
"""

from abc import ABC, abstractmethod
from dataclasses import dataclass, field
from datetime import datetime, date, time, timedelta
from typing import Optional, List, Tuple


@dataclass
class Event:
    """Unified calendar event representation across backends."""

    uid: str
    title: str
    start: datetime
    end: datetime
    location: str = ""
    description: str = ""
    calendar: str = ""
    all_day: bool = False
    recurring: bool = False
    organizer: str = ""
    url: str = ""
    categories: str = ""
    status: str = ""  # CONFIRMED, TENTATIVE, CANCELLED

    @property
    def duration_minutes(self) -> int:
        """Get duration in minutes."""
        delta = self.end - self.start
        return int(delta.total_seconds() / 60)

    @property
    def start_time(self) -> time:
        """Get start time."""
        return self.start.time()

    @property
    def end_time(self) -> time:
        """Get end time."""
        return self.end.time()

    @property
    def date(self) -> date:
        """Get the date of the event."""
        return self.start.date()

    def overlaps(self, other: "Event") -> bool:
        """Check if this event overlaps with another."""
        return self.start < other.end and self.end > other.start

    def get_row_span(self, minutes_per_row: int = 30) -> Tuple[int, int]:
        """Get the row range for this event in a grid.

        Args:
            minutes_per_row: Minutes each row represents (default 30)

        Returns:
            Tuple of (start_row, end_row) where rows are 0-indexed from midnight
        """
        start_minutes = self.start.hour * 60 + self.start.minute
        end_minutes = self.end.hour * 60 + self.end.minute

        # Handle events ending at midnight (next day)
        if end_minutes == 0 and self.end.date() > self.start.date():
            end_minutes = 24 * 60

        start_row = start_minutes // minutes_per_row
        end_row = (end_minutes + minutes_per_row - 1) // minutes_per_row  # Round up

        return start_row, end_row


class CalendarBackend(ABC):
    """Abstract base class for calendar backends."""

    @abstractmethod
    def get_events(
        self,
        start_date: date,
        end_date: date,
        calendar: Optional[str] = None,
    ) -> List[Event]:
        """Get events in a date range.

        Args:
            start_date: Start of range (inclusive)
            end_date: End of range (inclusive)
            calendar: Optional calendar name to filter by

        Returns:
            List of events in the range, sorted by start time
        """
        pass

    @abstractmethod
    def get_event(self, uid: str) -> Optional[Event]:
        """Get a single event by UID.

        Args:
            uid: Event unique identifier

        Returns:
            Event if found, None otherwise
        """
        pass

    @abstractmethod
    def get_calendars(self) -> List[str]:
        """Get list of available calendar names.

        Returns:
            List of calendar names
        """
        pass

    @abstractmethod
    def create_event(
        self,
        title: str,
        start: datetime,
        end: datetime,
        calendar: Optional[str] = None,
        location: Optional[str] = None,
        description: Optional[str] = None,
        all_day: bool = False,
    ) -> Event:
        """Create a new event.

        Args:
            title: Event title
            start: Start datetime
            end: End datetime
            calendar: Calendar to add event to
            location: Event location
            description: Event description
            all_day: Whether this is an all-day event

        Returns:
            The created event
        """
        pass

    @abstractmethod
    def delete_event(self, uid: str) -> bool:
        """Delete an event.

        Args:
            uid: Event unique identifier

        Returns:
            True if deleted successfully
        """
        pass

    @abstractmethod
    def update_event(
        self,
        uid: str,
        title: Optional[str] = None,
        start: Optional[datetime] = None,
        end: Optional[datetime] = None,
        location: Optional[str] = None,
        description: Optional[str] = None,
    ) -> Optional[Event]:
        """Update an existing event.

        Args:
            uid: Event unique identifier
            title: New title (if provided)
            start: New start time (if provided)
            end: New end time (if provided)
            location: New location (if provided)
            description: New description (if provided)

        Returns:
            Updated event if successful, None otherwise
        """
        pass

    def get_week_events(
        self,
        week_start: date,
        include_weekends: bool = True,
    ) -> dict[date, List[Event]]:
        """Get events for a week, grouped by date.

        Args:
            week_start: First day of the week
            include_weekends: Whether to include Saturday/Sunday

        Returns:
            Dict mapping dates to lists of events
        """
        days = 7 if include_weekends else 5
        end_date = week_start + timedelta(days=days - 1)
        events = self.get_events(week_start, end_date)

        # Group by date
        by_date: dict[date, List[Event]] = {}
        for i in range(days):
            d = week_start + timedelta(days=i)
            by_date[d] = []

        for event in events:
            event_date = event.date
            if event_date in by_date:
                by_date[event_date].append(event)

        # Sort each day's events by start time
        for d in by_date:
            by_date[d].sort(key=lambda e: e.start)

        return by_date