from datetime import datetime

from fastapi import APIRouter, Depends, HTTPException, Path, Query
from pydantic import BaseModel
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy import func, 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.models.calendar_member import CalendarMember
from app.schemas.calendar import CalendarCreate, CalendarUpdate, CalendarResponse
from app.services.calendar_sharing import require_permission
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)
        .where(Calendar.user_id == current_user.id)
        .order_by(Calendar.is_default.desc(), Calendar.name.asc())
    )
    calendars = result.scalars().all()

    # Populate member_count for shared calendars
    cal_ids = [c.id for c in calendars if c.is_shared]
    count_map: dict[int, int] = {}
    if cal_ids:
        counts = await db.execute(
            select(CalendarMember.calendar_id, func.count())
            .where(
                CalendarMember.calendar_id.in_(cal_ids),
                CalendarMember.status == "accepted",
            )
            .group_by(CalendarMember.calendar_id)
        )
        count_map = dict(counts.all())

    return [
        CalendarResponse.model_validate(c, from_attributes=True).model_copy(
            update={"member_count": count_map.get(c.id, 0)}
        )
        for c in calendars
    ]


@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,
        user_id=current_user.id,
    )
    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 = Path(ge=1, le=2147483647),
    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.user_id == current_user.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 = Path(ge=1, le=2147483647),
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user)
):
    result = await db.execute(
        select(Calendar).where(Calendar.id == calendar_id, Calendar.user_id == current_user.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 user's default calendar
    default_result = await db.execute(
        select(Calendar).where(
            Calendar.user_id == current_user.id,
            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


# ──────────────────────────────────────────────
# DELTA POLLING
# ──────────────────────────────────────────────

class CalendarPollResponse(BaseModel):
    has_changes: bool
    calendar_updated_at: str | None = None
    changed_event_ids: list[int] = []


@router.get("/{calendar_id}/poll", response_model=CalendarPollResponse)
async def poll_calendar(
    calendar_id: int = Path(ge=1, le=2147483647),
    since: str = Query(..., description="ISO timestamp to check for changes since"),
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user)
):
    """Lightweight poll endpoint — returns changed event IDs since timestamp."""
    await require_permission(db, calendar_id, current_user.id, "read_only")

    try:
        since_dt = datetime.fromisoformat(since)
    except ValueError:
        raise HTTPException(status_code=400, detail="Invalid ISO timestamp")

    # Check calendar-level update
    cal_result = await db.execute(
        select(Calendar.updated_at).where(Calendar.id == calendar_id)
    )
    calendar_updated = cal_result.scalar_one_or_none()
    if not calendar_updated:
        raise HTTPException(status_code=404, detail="Calendar not found")

    calendar_changed = calendar_updated > since_dt

    # Check event-level changes using the ix_events_calendar_updated index
    event_result = await db.execute(
        select(CalendarEvent.id).where(
            CalendarEvent.calendar_id == calendar_id,
            CalendarEvent.updated_at > since_dt,
        )
    )
    changed_event_ids = [r[0] for r in event_result.all()]

    has_changes = calendar_changed or len(changed_event_ids) > 0

    return CalendarPollResponse(
        has_changes=has_changes,
        calendar_updated_at=calendar_updated.isoformat() if calendar_updated else None,
        changed_event_ids=changed_event_ids,
    )