import json
from fastapi import APIRouter, Depends, HTTPException, Path, Query
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy import false as sa_false, select, delete, or_
from sqlalchemy.orm import selectinload
from typing import Optional, List, Any, Literal

from datetime import date, datetime, timedelta

from app.database import get_db
from app.models.calendar_event import CalendarEvent
from app.models.calendar import Calendar
from app.models.person import Person
from app.schemas.calendar_event import (
    CalendarEventCreate,
    CalendarEventUpdate,
    CalendarEventResponse,
)
from app.routers.auth import get_current_user
from app.models.user import User
from app.services.recurrence import generate_occurrences
from app.services.calendar_sharing import check_lock_for_edit, get_accessible_calendar_ids, get_accessible_event_scope, require_permission
from app.services.event_invitation import get_invited_event_ids, get_invitation_overrides_for_user
from app.models.event_invitation import EventInvitation

router = APIRouter()


def _event_to_dict(
    event: CalendarEvent,
    is_invited: bool = False,
    invitation_status: str | None = None,
    invitation_id: int | None = None,
    display_calendar_id: int | None = None,
    display_calendar_name: str | None = None,
    display_calendar_color: str | None = None,
    can_modify: bool = False,
) -> dict:
    """Serialize a CalendarEvent ORM object to a response dict including calendar info."""
    # For invited events: use display calendar if set, otherwise fallback to "Invited"/gray
    if is_invited:
        if display_calendar_name:
            cal_name = display_calendar_name
            cal_color = display_calendar_color or "#6B7280"
        else:
            cal_name = "Invited"
            cal_color = "#6B7280"
    else:
        cal_name = event.calendar.name if event.calendar else ""
        cal_color = event.calendar.color if event.calendar else ""

    d = {
        "id": event.id,
        "title": event.title,
        "description": event.description,
        "start_datetime": event.start_datetime,
        "end_datetime": event.end_datetime,
        "all_day": event.all_day,
        "color": event.color,
        "location_id": event.location_id,
        "recurrence_rule": event.recurrence_rule,
        "is_starred": event.is_starred,
        "calendar_id": event.calendar_id,
        "calendar_name": cal_name,
        "calendar_color": cal_color,
        "is_virtual": False,
        "parent_event_id": event.parent_event_id,
        "is_recurring": event.is_recurring,
        "original_start": event.original_start,
        "created_at": event.created_at,
        "updated_at": event.updated_at,
        "is_invited": is_invited,
        "invitation_status": invitation_status,
        "invitation_id": invitation_id,
        "display_calendar_id": display_calendar_id,
        "can_modify": can_modify,
    }
    return d


def _birthday_events_for_range(
    people: list,
    bday_calendar_id: int,
    bday_calendar_color: str,
    start: Optional[date],
    end: Optional[date],
) -> list[dict]:
    """Generate virtual all-day birthday events for each person within the date range."""
    virtual_events = []
    now = datetime.now()
    range_start = start or date(now.year - 1, 1, 1)
    range_end = end or date(now.year + 2, 12, 31)

    for person in people:
        if not person.birthday:
            continue

        bday: date = person.birthday
        for year in range(range_start.year, range_end.year + 1):
            try:
                bday_this_year = bday.replace(year=year)
            except ValueError:
                # Feb 29 on non-leap year — skip
                continue

            if bday_this_year < range_start or bday_this_year > range_end:
                continue

            start_dt = datetime(bday_this_year.year, bday_this_year.month, bday_this_year.day, 0, 0, 0)
            end_dt = start_dt + timedelta(days=1)
            age = year - bday.year

            virtual_events.append({
                "id": f"bday-{person.id}-{year}",
                "title": f"{person.name}'s Birthday" + (f" ({age})" if age > 0 else ""),
                "description": None,
                "start_datetime": start_dt,
                "end_datetime": end_dt,
                "all_day": True,
                "color": bday_calendar_color,
                "location_id": None,
                "recurrence_rule": None,
                "is_starred": False,
                "calendar_id": bday_calendar_id,
                "calendar_name": "Birthdays",
                "calendar_color": bday_calendar_color,
                "is_virtual": True,
                "parent_event_id": None,
                "is_recurring": False,
                "original_start": None,
                "created_at": start_dt,
                "updated_at": start_dt,
            })

    return virtual_events


async def _get_default_calendar_id(db: AsyncSession, user_id: int) -> int:
    """Return the id of the user's default calendar, raising 500 if not found."""
    result = await db.execute(
        select(Calendar).where(
            Calendar.user_id == user_id,
            Calendar.is_default == True,
        )
    )
    default = result.scalar_one_or_none()
    if not default:
        raise HTTPException(status_code=500, detail="No default calendar configured")
    return default.id


async def _verify_calendar_ownership(db: AsyncSession, calendar_id: int, user_id: int) -> None:
    """Raise 404 if calendar_id does not belong to user_id (SEC-04)."""
    result = await db.execute(
        select(Calendar).where(Calendar.id == calendar_id, Calendar.user_id == user_id)
    )
    if not result.scalar_one_or_none():
        raise HTTPException(status_code=404, detail="Calendar not found")


@router.get("/", response_model=None)
async def get_events(
    start: Optional[date] = Query(None, ge=date(2020, 1, 1), le=date(2099, 12, 31)),
    end: Optional[date] = Query(None, ge=date(2020, 1, 1), le=date(2099, 12, 31)),
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user),
) -> List[Any]:
    """
    Get all calendar events with optional date range filtering.

    Parent template rows (is_recurring=True, parent_event_id IS NULL,
    recurrence_rule IS NOT NULL) are excluded — their materialised children
    are what get displayed on the calendar.
    """
    # Scope events through calendar ownership + shared memberships + invitations
    all_calendar_ids, invited_event_ids = await get_accessible_event_scope(current_user.id, db)


    query = (
        select(CalendarEvent)
        .options(selectinload(CalendarEvent.calendar))
        .where(
            or_(
                CalendarEvent.calendar_id.in_(all_calendar_ids),
                CalendarEvent.id.in_(invited_event_ids) if invited_event_ids else sa_false(),
                CalendarEvent.parent_event_id.in_(invited_event_ids) if invited_event_ids else sa_false(),
            )
        )
    )

    # Exclude parent template rows — they are not directly rendered
    query = query.where(
        ~(
            (CalendarEvent.is_recurring == True)
            & (CalendarEvent.parent_event_id == None)
            & (CalendarEvent.recurrence_rule != None)
        )
    )

    if start:
        query = query.where(CalendarEvent.end_datetime >= start)
    if end:
        query = query.where(CalendarEvent.start_datetime <= end)

    query = query.order_by(CalendarEvent.start_datetime.asc()).limit(2000)

    result = await db.execute(query)
    events = result.scalars().all()

    # Build invitation lookup for the current user
    invited_event_id_set = set(invited_event_ids)
    invitation_map: dict[int, tuple[str, int, int | None, bool]] = {}  # event_id -> (status, invitation_id, display_calendar_id, can_modify)
    if invited_event_ids:
        inv_result = await db.execute(
            select(
                EventInvitation.event_id,
                EventInvitation.status,
                EventInvitation.id,
                EventInvitation.display_calendar_id,
                EventInvitation.can_modify,
            ).where(
                EventInvitation.user_id == current_user.id,
                EventInvitation.event_id.in_(invited_event_ids),
            )
        )
        for eid, status, inv_id, disp_cal_id, cm in inv_result.all():
            invitation_map[eid] = (status, inv_id, disp_cal_id, cm)

    # Batch-fetch display calendars for invited events
    display_cal_ids = {t[2] for t in invitation_map.values() if t[2] is not None}
    display_cal_map: dict[int, dict] = {}  # cal_id -> {name, color}
    if display_cal_ids:
        cal_result = await db.execute(
            select(Calendar.id, Calendar.name, Calendar.color).where(
                Calendar.id.in_(display_cal_ids),
                Calendar.id.in_(all_calendar_ids),
            )
        )
        for cal_id, cal_name, cal_color in cal_result.all():
            display_cal_map[cal_id] = {"name": cal_name, "color": cal_color}

    # Get per-occurrence overrides for invited events
    all_event_ids = [e.id for e in events]
    override_map = await get_invitation_overrides_for_user(db, current_user.id, all_event_ids)

    response: List[dict] = []
    for e in events:
        # Determine if this event is from an invitation
        parent_id = e.parent_event_id or e.id
        is_invited = parent_id in invited_event_id_set
        inv_status = None
        inv_id = None
        disp_cal_id = None
        disp_cal_name = None
        disp_cal_color = None
        inv_can_modify = False
        if is_invited and parent_id in invitation_map:
            inv_status, inv_id, disp_cal_id, inv_can_modify = invitation_map[parent_id]
            # Check for per-occurrence override
            if e.id in override_map:
                inv_status = override_map[e.id]
            # Resolve display calendar info
            if disp_cal_id and disp_cal_id in display_cal_map:
                disp_cal_name = display_cal_map[disp_cal_id]["name"]
                disp_cal_color = display_cal_map[disp_cal_id]["color"]
        response.append(_event_to_dict(
            e,
            is_invited=is_invited,
            invitation_status=inv_status,
            invitation_id=inv_id,
            display_calendar_id=disp_cal_id,
            display_calendar_name=disp_cal_name,
            display_calendar_color=disp_cal_color,
            can_modify=inv_can_modify,
        ))

    # Fetch the user's Birthdays system calendar; only generate virtual events if visible
    bday_result = await db.execute(
        select(Calendar).where(
            Calendar.user_id == current_user.id,
            Calendar.name == "Birthdays",
            Calendar.is_system == True,
        )
    )
    bday_calendar = bday_result.scalar_one_or_none()

    if bday_calendar and bday_calendar.is_visible:
        # Scope birthday people to this user
        people_result = await db.execute(
            select(Person).where(
                Person.user_id == current_user.id,
                Person.birthday.isnot(None),
            )
        )
        people = people_result.scalars().all()

        virtual = _birthday_events_for_range(
            people=people,
            bday_calendar_id=bday_calendar.id,
            bday_calendar_color=bday_calendar.color,
            start=start,
            end=end,
        )
        response.extend(virtual)

    return response


@router.post("/", response_model=CalendarEventResponse, status_code=201)
async def create_event(
    event: CalendarEventCreate,
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    if event.end_datetime < event.start_datetime:
        raise HTTPException(status_code=400, detail="End datetime must be after start datetime")

    data = event.model_dump()

    # Resolve calendar_id to user's default if not provided
    if not data.get("calendar_id"):
        data["calendar_id"] = await _get_default_calendar_id(db, current_user.id)
    else:
        # SEC-04: verify ownership OR shared calendar permission
        cal_ownership_result = await db.execute(
            select(Calendar).where(Calendar.id == data["calendar_id"], Calendar.user_id == current_user.id)
        )
        if not cal_ownership_result.scalar_one_or_none():
            # Not owned — check shared calendar permission
            await require_permission(db, data["calendar_id"], current_user.id, "create_modify")

    # Serialize RecurrenceRule object to JSON string for DB storage
    # Exclude None values so defaults in recurrence service work correctly
    rule_obj = data.pop("recurrence_rule", None)
    rule_json: Optional[str] = json.dumps({k: v for k, v in rule_obj.items() if v is not None}) if rule_obj else None

    if rule_json:
        # Parent template: is_recurring=True, no parent_event_id
        parent = CalendarEvent(**data, recurrence_rule=rule_json, is_recurring=True, updated_by=current_user.id)
        db.add(parent)
        await db.flush()  # assign parent.id before generating children

        children = generate_occurrences(parent)
        db.add_all(children)

        await db.commit()

        # Return the first child so the caller sees a concrete occurrence
        # (The parent template is intentionally hidden from list views)
        if children:
            result = await db.execute(
                select(CalendarEvent)
                .options(selectinload(CalendarEvent.calendar))
                .where(CalendarEvent.id == children[0].id)
            )
            return result.scalar_one()

        # Fallback: no children generated (e.g. bad rule), return parent
        result = await db.execute(
            select(CalendarEvent)
            .options(selectinload(CalendarEvent.calendar))
            .where(CalendarEvent.id == parent.id)
        )
        return result.scalar_one()

    else:
        new_event = CalendarEvent(**data, recurrence_rule=None, updated_by=current_user.id)
        db.add(new_event)
        await db.commit()

        result = await db.execute(
            select(CalendarEvent)
            .options(selectinload(CalendarEvent.calendar))
            .where(CalendarEvent.id == new_event.id)
        )
        return result.scalar_one()


@router.get("/{event_id}", response_model=CalendarEventResponse)
async def get_event(
    event_id: int = Path(ge=1, le=2147483647),
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    all_calendar_ids, invited_event_ids = await get_accessible_event_scope(current_user.id, db)
    invited_set = set(invited_event_ids)


    result = await db.execute(
        select(CalendarEvent)
        .options(selectinload(CalendarEvent.calendar))
        .where(
            CalendarEvent.id == event_id,
            or_(
                CalendarEvent.calendar_id.in_(all_calendar_ids),
                CalendarEvent.id.in_(invited_event_ids) if invited_event_ids else sa_false(),
                CalendarEvent.parent_event_id.in_(invited_event_ids) if invited_event_ids else sa_false(),
            ),
        )
    )
    event = result.scalar_one_or_none()

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

    return event


@router.put("/{event_id}", response_model=CalendarEventResponse)
async def update_event(
    event_id: int = Path(ge=1, le=2147483647),
    event_update: CalendarEventUpdate = ...,
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    # IMPORTANT: Uses get_accessible_calendar_ids (NOT get_accessible_event_scope).
    # Event invitees can VIEW events but must NOT be able to edit them
    # UNLESS they have can_modify=True (checked in fallback path below).
    all_calendar_ids = await get_accessible_calendar_ids(current_user.id, db)
    is_invited_editor = False

    result = await db.execute(
        select(CalendarEvent)
        .options(selectinload(CalendarEvent.calendar))
        .where(
            CalendarEvent.id == event_id,
            CalendarEvent.calendar_id.in_(all_calendar_ids),
        )
    )
    event = result.scalar_one_or_none()

    if not event:
        # Fallback: check if user has can_modify invitation for this event
        # Must check both event_id (direct) and parent_event_id (recurring child)
        # because invitations are stored against the parent event
        target_event_result = await db.execute(
            select(CalendarEvent.parent_event_id).where(CalendarEvent.id == event_id)
        )
        target_row = target_event_result.one_or_none()
        if not target_row:
            raise HTTPException(status_code=404, detail="Calendar event not found")
        candidate_ids = [event_id]
        if target_row[0] is not None:
            candidate_ids.append(target_row[0])

        inv_result = await db.execute(
            select(EventInvitation).where(
                EventInvitation.event_id.in_(candidate_ids),
                EventInvitation.user_id == current_user.id,
                EventInvitation.can_modify == True,
                EventInvitation.status.in_(["accepted", "tentative"]),
            )
        )
        inv = inv_result.scalar_one_or_none()
        if not inv:
            raise HTTPException(status_code=404, detail="Calendar event not found")

        # Load the event directly (bypassing calendar filter)
        event_result = await db.execute(
            select(CalendarEvent)
            .options(selectinload(CalendarEvent.calendar))
            .where(CalendarEvent.id == event_id)
        )
        event = event_result.scalar_one_or_none()
        if not event:
            raise HTTPException(status_code=404, detail="Calendar event not found")
        is_invited_editor = True

    update_data = event_update.model_dump(exclude_unset=True)

    if is_invited_editor:
        # Invited editor restrictions — enforce BEFORE any data mutation
        scope_peek = update_data.get("edit_scope")
        # Block all bulk-scope edits on recurring events (C-01/F-01)
        if event.is_recurring and scope_peek != "this":
            raise HTTPException(status_code=403, detail="Invited editors can only edit individual occurrences")
        # Block calendar moves (C-02)
        if "calendar_id" in update_data and update_data["calendar_id"] != event.calendar_id:
            raise HTTPException(status_code=403, detail="Invited editors cannot move events between calendars")
    else:
        # Standard calendar-access path: require create_modify+ permission
        await require_permission(db, event.calendar_id, current_user.id, "create_modify")

    # Lock check applies to both paths (uses owner's calendar_id)
    await check_lock_for_edit(db, event_id, current_user.id, event.calendar_id)

    # Extract scope before applying fields to the model
    scope: Optional[str] = update_data.pop("edit_scope", None)

    # Serialize RecurrenceRule → JSON string if present in update payload
    rule_obj = update_data.pop("recurrence_rule", None)
    if rule_obj is not None:
        update_data["recurrence_rule"] = json.dumps({k: v for k, v in rule_obj.items() if v is not None}) if rule_obj else None

    if not is_invited_editor:
        # SEC-04: if calendar_id is being changed, verify the target belongs to the user
        # Only verify ownership when the calendar is actually changing — members submitting
        # an unchanged calendar_id must not be rejected just because they aren't the owner.
        if "calendar_id" in update_data and update_data["calendar_id"] is not None and update_data["calendar_id"] != event.calendar_id:
            await _verify_calendar_ownership(db, update_data["calendar_id"], current_user.id)

        # M-01: Block non-owners from moving events off shared calendars
        if "calendar_id" in update_data and update_data["calendar_id"] != event.calendar_id:
            source_cal_result = await db.execute(
                select(Calendar).where(Calendar.id == event.calendar_id)
            )
            source_cal = source_cal_result.scalar_one_or_none()
            if source_cal and source_cal.is_shared and source_cal.user_id != current_user.id:
                raise HTTPException(
                    status_code=403,
                    detail="Only the calendar owner can move events between calendars",
                )

    start = update_data.get("start_datetime", event.start_datetime)
    end_dt = update_data.get("end_datetime", event.end_datetime)
    if end_dt is not None and end_dt < start:
        raise HTTPException(status_code=400, detail="End datetime must be after start datetime")

    if scope == "this":
        # Update only this occurrence and detach it from the series
        for key, value in update_data.items():
            setattr(event, key, value)
        # Detach from parent so it's an independent event going forward
        event.parent_event_id = None
        event.is_recurring = False
        event.updated_by = current_user.id
        await db.commit()

    elif scope == "this_and_future":
        # Delete all future siblings (same parent, original_start >= this event's original_start)
        parent_id = event.parent_event_id
        this_original_start = event.original_start or event.start_datetime

        if parent_id is not None:
            # Fetch the parent's recurrence_rule before deleting siblings
            parent_result = await db.execute(
                select(CalendarEvent).where(CalendarEvent.id == parent_id)
            )
            parent_event = parent_result.scalar_one_or_none()
            parent_rule = parent_event.recurrence_rule if parent_event else None

            await db.execute(
                delete(CalendarEvent).where(
                    CalendarEvent.parent_event_id == parent_id,
                    CalendarEvent.original_start >= this_original_start,
                    CalendarEvent.id != event_id,
                )
            )

            # Update this event with the new data, making it a new parent
            for key, value in update_data.items():
                setattr(event, key, value)
            event.parent_event_id = None
            event.is_recurring = True
            event.original_start = None
            event.updated_by = current_user.id

            # Inherit parent's recurrence_rule if none was provided in update
            if not event.recurrence_rule and parent_rule:
                event.recurrence_rule = parent_rule

            # Regenerate children from this point
            if event.recurrence_rule:
                await db.flush()
                children = generate_occurrences(event)
                db.add_all(children)
        else:
            # This IS a parent — update it and regenerate all children
            for key, value in update_data.items():
                setattr(event, key, value)
            event.updated_by = current_user.id

            # Delete all existing children and regenerate
            if event.recurrence_rule:
                await db.execute(
                    delete(CalendarEvent).where(
                        CalendarEvent.parent_event_id == event.id
                    )
                )
                await db.flush()
                children = generate_occurrences(event)
                db.add_all(children)

        await db.commit()

    else:
        # No scope — plain update (non-recurring events or full-series metadata)
        for key, value in update_data.items():
            setattr(event, key, value)
        event.updated_by = current_user.id
        await db.commit()

    result = await db.execute(
        select(CalendarEvent)
        .options(selectinload(CalendarEvent.calendar))
        .where(CalendarEvent.id == event_id)
    )
    updated = result.scalar_one_or_none()
    if not updated:
        # Event was deleted as part of this_and_future; 404 is appropriate
        raise HTTPException(status_code=404, detail="Event no longer exists after update")
    return updated


@router.delete("/{event_id}", status_code=204)
async def delete_event(
    event_id: int = Path(ge=1, le=2147483647),
    scope: Optional[Literal["this", "this_and_future"]] = Query(None),
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    # IMPORTANT: Uses get_accessible_calendar_ids (NOT get_accessible_event_scope).
    # Event invitees can VIEW events but must NOT be able to delete them.
    # Invitees use DELETE /api/event-invitations/{id} to leave instead.
    all_calendar_ids = await get_accessible_calendar_ids(current_user.id, db)

    result = await db.execute(
        select(CalendarEvent).where(
            CalendarEvent.id == event_id,
            CalendarEvent.calendar_id.in_(all_calendar_ids),
        )
    )
    event = result.scalar_one_or_none()

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

    # Shared calendar: require full_access+ and check lock
    await require_permission(db, event.calendar_id, current_user.id, "full_access")
    await check_lock_for_edit(db, event_id, current_user.id, event.calendar_id)

    if scope == "this":
        # Delete just this one occurrence
        await db.delete(event)

    elif scope == "this_and_future":
        parent_id = event.parent_event_id
        this_original_start = event.original_start or event.start_datetime

        if parent_id is not None:
            # Delete this + all future siblings (original_start is always set on children)
            await db.execute(
                delete(CalendarEvent).where(
                    CalendarEvent.parent_event_id == parent_id,
                    CalendarEvent.original_start >= this_original_start,
                )
            )
        else:
            # This event IS the parent — delete it and all children (CASCADE handles children)
            await db.delete(event)

    else:
        # Plain delete (non-recurring; or delete entire series if parent)
        await db.delete(event)

    await db.commit()
    return None