from fastapi import APIRouter, Depends, HTTPException
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy import select, update
from typing import List

from app.database import get_db
from app.models.calendar import Calendar
from app.models.calendar_event import CalendarEvent
from app.schemas.calendar import CalendarCreate, CalendarUpdate, CalendarResponse
from app.routers.auth import get_current_user
from app.models.user import User

router = APIRouter()


@router.get("/", response_model=List[CalendarResponse])
async def get_calendars(
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user)
):
    result = await db.execute(select(Calendar).order_by(Calendar.is_default.desc(), Calendar.name.asc()))
    return result.scalars().all()


@router.post("/", response_model=CalendarResponse, status_code=201)
async def create_calendar(
    calendar: CalendarCreate,
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user)
):
    new_calendar = Calendar(
        name=calendar.name,
        color=calendar.color,
        is_default=False,
        is_system=False,
        is_visible=True,
    )
    db.add(new_calendar)
    await db.commit()
    await db.refresh(new_calendar)
    return new_calendar


@router.put("/{calendar_id}", response_model=CalendarResponse)
async def update_calendar(
    calendar_id: int,
    calendar_update: CalendarUpdate,
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user)
):
    result = await db.execute(select(Calendar).where(Calendar.id == calendar_id))
    calendar = result.scalar_one_or_none()

    if not calendar:
        raise HTTPException(status_code=404, detail="Calendar not found")

    update_data = calendar_update.model_dump(exclude_unset=True)

    # System calendars: allow visibility toggle but block name changes
    if calendar.is_system and "name" in update_data:
        raise HTTPException(status_code=400, detail="Cannot rename system calendars")

    for key, value in update_data.items():
        setattr(calendar, key, value)

    await db.commit()
    await db.refresh(calendar)
    return calendar


@router.delete("/{calendar_id}", status_code=204)
async def delete_calendar(
    calendar_id: int,
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user)
):
    result = await db.execute(select(Calendar).where(Calendar.id == calendar_id))
    calendar = result.scalar_one_or_none()

    if not calendar:
        raise HTTPException(status_code=404, detail="Calendar not found")

    if calendar.is_system:
        raise HTTPException(status_code=400, detail="Cannot delete system calendars")

    if calendar.is_default:
        raise HTTPException(status_code=400, detail="Cannot delete the default calendar")

    # Reassign all events on this calendar to the default calendar
    default_result = await db.execute(select(Calendar).where(Calendar.is_default == True))
    default_calendar = default_result.scalar_one_or_none()

    if default_calendar:
        await db.execute(
            update(CalendarEvent)
            .where(CalendarEvent.calendar_id == calendar_id)
            .values(calendar_id=default_calendar.id)
        )

    await db.delete(calendar)
    await db.commit()
    return None