import uuid
from datetime import datetime, timezone
from typing import List, Optional

from fastapi import APIRouter, Depends, Form, HTTPException, Query, Request, UploadFile, File
from fastapi.responses import Response
from pydantic import BaseModel
from sqlalchemy.orm import Session

import dav_util
import ical_io
import models
import permissions
from auth import get_current_user
from database import get_db
from local_events_util import build_local_event_dict, resolve_creator

router = APIRouter()


def _now_iso() -> str:
    return datetime.now(timezone.utc).isoformat()


class CalendarCreate(BaseModel):
    name: str
    color: str = "#34a853"
    is_birthday: bool = False
    birthday_notify_days_before: Optional[int] = None


class CalendarUpdate(BaseModel):
    name: Optional[str] = None
    color: Optional[str] = None
    enabled: Optional[bool] = None
    sidebar_hidden: Optional[bool] = None
    reminders_enabled: Optional[bool] = None
    caldav_published: Optional[bool] = None
    is_birthday: Optional[bool] = None
    birthday_notify_days_before: Optional[int] = None


class EventCreate(BaseModel):
    calendar_id: int
    title: str
    start: str
    end: str
    allDay: bool = False
    location: Optional[str] = None
    description: Optional[str] = None
    color: Optional[str] = None
    rrule: Optional[str] = None
    private: bool = False
    reminders: Optional[List[int]] = None  # minutes before start (0 = at start)
    external_uid: Optional[str] = None  # stable id for imported entries (Contacts dedup)
    birth_year: Optional[int] = None    # birthday events; NULL = year unknown


class EventUpdate(BaseModel):
    title: Optional[str] = None
    start: Optional[str] = None
    end: Optional[str] = None
    allDay: Optional[bool] = None
    location: Optional[str] = None
    description: Optional[str] = None
    color: Optional[str] = None
    rrule: Optional[str] = None
    exdate: Optional[str] = None
    private: Optional[bool] = None
    reminders: Optional[List[int]] = None
    external_uid: Optional[str] = None
    birth_year: Optional[int] = None


class ShareCreate(BaseModel):
    user_id: int
    permission: str = "read"


def _cal_dict(cal: models.LocalCalendar, *, owned: bool = True,
              shared_by: Optional[str] = None, permission: Optional[str] = None,
              color_override: Optional[str] = None,
              request: Optional[Request] = None) -> dict:
    d = {
        "id": cal.id,
        # A shared calendar is labelled by the person/group it comes from — the
        # owner's real calendar name must never reach recipients.
        "name": shared_by if (not owned and shared_by is not None) else cal.name,
        # A recipient's own colour for a shared calendar wins over the owner's.
        "color": color_override or cal.color,
        "enabled": cal.enabled,
        "sidebar_hidden": bool(cal.sidebar_hidden),
        "reminders_enabled": bool(cal.reminders_enabled),
        "caldav_published": bool(cal.caldav_published),
        "is_birthday": bool(cal.is_birthday),
        "birthday_notify_days_before": cal.birthday_notify_days_before,
        "type": "local",
        "owned": owned,
    }
    # Only the owner may publish; expose the subscribe URLs only when active.
    if owned and cal.caldav_published and cal.dav_token:
        d["caldav_url"] = dav_util.caldav_url(request, cal.dav_token) if request else None
        d["caldav_login_url"] = dav_util.caldav_login_url(request) if request else None
    if shared_by is not None:
        d["shared_by"] = shared_by
    if permission is not None:
        d["permission"] = permission
    return d


def _event_dict(ev: models.LocalEvent, cal: models.LocalCalendar, db: Session) -> dict:
    return build_local_event_dict(ev, cal, creator=resolve_creator(ev))


# ── Calendar CRUD ─────────────────────────────────────────

@router.get("/calendars")
def list_calendars(
    request: Request,
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    # Map calendar_id -> group name for every group the user belongs to, so we
    # can flag group calendars as such even when the user owns them (the creator
    # owns the group calendar — it must still be marked group:true).
    group_cal_map = {
        cal_id: name
        for cal_id, name in (
            db.query(models.GroupCalendar.calendar_id, models.Group.name)
            .join(models.Group, models.Group.id == models.GroupCalendar.group_id)
            .join(models.GroupMember, models.GroupMember.group_id == models.GroupCalendar.group_id)
            .filter(models.GroupMember.user_id == current_user.id)
            .all()
        )
    }

    # Per-user colour overrides for calendars the user doesn't own (any sharing path).
    color_prefs = permissions.color_prefs_for(db, current_user.id)

    # Own calendars
    own = (
        db.query(models.LocalCalendar)
        .filter(models.LocalCalendar.user_id == current_user.id)
        .all()
    )
    result = []
    for c in own:
        d = _cal_dict(c, owned=True, request=request)
        if c.id in group_cal_map:
            d["group"] = True
            d["shared_by"] = group_cal_map[c.id]  # group name, for labelling
        result.append(d)

    seen_ids = {c.id for c in own}

    # Calendars shared with this user
    shares = (
        db.query(models.CalendarShare)
        .filter(models.CalendarShare.user_id == current_user.id)
        .all()
    )
    for share in shares:
        cal = share.calendar
        if cal is None or cal.id in seen_ids:
            continue
        seen_ids.add(cal.id)
        owner = db.query(models.User).filter(models.User.id == cal.user_id).first()
        d = _cal_dict(
            cal, owned=False,
            shared_by=(owner.display_name or owner.username) if owner else None,
            permission=share.permission,
            color_override=color_prefs.get(cal.id),
        )
        if cal.id in group_cal_map:
            d["group"] = True
        result.append(d)

    # Group calendars reached via membership (read_write) that aren't already
    # listed, so members can select/see the group calendar.
    for cal_id, group_name in group_cal_map.items():
        if cal_id in seen_ids:
            continue
        cal = db.query(models.LocalCalendar).filter(models.LocalCalendar.id == cal_id).first()
        if not cal:
            continue
        seen_ids.add(cal_id)
        d = _cal_dict(cal, owned=False, shared_by=group_name, permission="read_write",
                      color_override=color_prefs.get(cal.id))
        d["group"] = True
        result.append(d)

    # Calendars co-members share into shared groups (group_visible_calendar_id).
    # Read-only, shown under the owner's name. Deduped against everything above
    # so a calendar already shared directly / as a group calendar isn't doubled.
    for cal in permissions.co_member_group_visible_calendars(db, current_user):
        if cal.id in seen_ids:
            continue
        seen_ids.add(cal.id)
        owner = db.query(models.User).filter(models.User.id == cal.user_id).first()
        d = _cal_dict(
            cal, owned=False,
            shared_by=(owner.display_name or owner.username) if owner else None,
            permission="read",
            color_override=color_prefs.get(cal.id),
            request=request,
        )
        d["group_shared"] = True
        result.append(d)
    return result


@router.post("/calendars")
def create_calendar(
    data: CalendarCreate,
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    # Only ONE birthday calendar per account — hard server guarantee. If the
    # user already has one, "create birthday calendar" is idempotent: return the
    # existing one instead of creating a second.
    if data.is_birthday:
        existing = (
            db.query(models.LocalCalendar)
            .filter(
                models.LocalCalendar.user_id == current_user.id,
                models.LocalCalendar.is_birthday == True,
            )
            .first()
        )
        if existing is not None:
            return _cal_dict(existing)

    cal = models.LocalCalendar(
        user_id=current_user.id,
        name=data.name,
        color=data.color,
        is_birthday=data.is_birthday,
        birthday_notify_days_before=data.birthday_notify_days_before,
    )
    db.add(cal)
    db.commit()
    db.refresh(cal)
    return _cal_dict(cal)


@router.put("/calendars/{calendar_id}")
def update_calendar(
    calendar_id: int,
    data: CalendarUpdate,
    request: Request,
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    cal = (
        db.query(models.LocalCalendar)
        .filter(
            models.LocalCalendar.id == calendar_id,
            models.LocalCalendar.user_id == current_user.id,
        )
        .first()
    )
    if not cal:
        raise HTTPException(404, "Calendar not found")
    if data.name is not None:
        cal.name = data.name
    if data.color is not None:
        cal.color = data.color
    if data.enabled is not None:
        cal.enabled = data.enabled
    if data.sidebar_hidden is not None:
        cal.sidebar_hidden = data.sidebar_hidden
    if data.reminders_enabled is not None:
        cal.reminders_enabled = data.reminders_enabled
    if data.is_birthday is not None:
        # Never let a second calendar be marked as the birthday calendar.
        if data.is_birthday and not cal.is_birthday:
            other = (
                db.query(models.LocalCalendar)
                .filter(
                    models.LocalCalendar.user_id == current_user.id,
                    models.LocalCalendar.is_birthday == True,
                    models.LocalCalendar.id != cal.id,
                )
                .first()
            )
            if other is not None:
                raise HTTPException(422, "A birthday calendar already exists")
        cal.is_birthday = data.is_birthday
    if data.birthday_notify_days_before is not None:
        # -1 is the client's sentinel for "clear the reminder" (JSON has no way to
        # send SQL NULL through an Optional that also means "unchanged").
        cal.birthday_notify_days_before = (
            None if data.birthday_notify_days_before < 0 else data.birthday_notify_days_before
        )
    if data.caldav_published is not None:
        cal.caldav_published = data.caldav_published
        if data.caldav_published:
            # First publish: mint a token + initial ctag so clients can sync.
            if not cal.dav_token:
                cal.dav_token = dav_util.new_token()
            if not cal.dav_ctag:
                cal.dav_ctag = dav_util.new_tag()
        else:
            # Unpublishing revokes access: drop the token so the URL 404s.
            cal.dav_token = None
    db.commit()
    db.refresh(cal)
    return _cal_dict(cal, owned=True, request=request)


class CalendarColorUpdate(BaseModel):
    color: str


@router.put("/calendars/{calendar_id}/color")
def set_calendar_color(
    calendar_id: int,
    data: CalendarColorUpdate,
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    """Set a calendar's colour. The owner changes the calendar's colour for
    everyone; anyone else who can see the calendar (direct share, group calendar,
    or a co-member's group-visible calendar) sets only their OWN per-user colour.
    Recipients may recolour but never rename a shared calendar."""
    cal = db.query(models.LocalCalendar).filter(models.LocalCalendar.id == calendar_id).first()
    if cal is None:
        raise HTTPException(404, "Calendar not found")
    if cal.user_id == current_user.id:
        cal.color = data.color
    else:
        if calendar_id not in permissions.readable_local_calendar_ids(db, current_user):
            raise HTTPException(403, "You cannot access this calendar")
        pref = (
            db.query(models.CalendarColorPref)
            .filter(
                models.CalendarColorPref.calendar_id == calendar_id,
                models.CalendarColorPref.user_id == current_user.id,
            )
            .first()
        )
        if pref:
            pref.color = data.color
        else:
            db.add(models.CalendarColorPref(
                calendar_id=calendar_id, user_id=current_user.id, color=data.color))
    db.commit()
    return {"ok": True, "color": data.color}


@router.post("/calendars/{calendar_id}/dav-token/rotate")
def rotate_dav_token(
    calendar_id: int,
    request: Request,
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    """Issue a fresh CalDAV token — the old subscribe URL stops working."""
    cal = (
        db.query(models.LocalCalendar)
        .filter(
            models.LocalCalendar.id == calendar_id,
            models.LocalCalendar.user_id == current_user.id,
        )
        .first()
    )
    if not cal:
        raise HTTPException(404, "Calendar not found")
    if not cal.caldav_published:
        raise HTTPException(422, "Calendar is not published")
    cal.dav_token = dav_util.new_token()
    cal.dav_ctag = dav_util.new_tag()
    db.commit()
    db.refresh(cal)
    return _cal_dict(cal, owned=True, request=request)


@router.delete("/calendars/{calendar_id}")
def delete_calendar(
    calendar_id: int,
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    cal = (
        db.query(models.LocalCalendar)
        .filter(
            models.LocalCalendar.id == calendar_id,
            models.LocalCalendar.user_id == current_user.id,
        )
        .first()
    )
    if not cal:
        raise HTTPException(404, "Calendar not found")
    db.delete(cal)
    db.commit()
    return {"ok": True}


# ── Event CRUD ────────────────────────────────────────────

@router.post("/events")
def create_event(
    data: EventCreate,
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    # Owner, shared (read_write), or group-member calendars are writable.
    cal = permissions.accessible_local_calendar(
        db, current_user, data.calendar_id, require_write=True
    )

    # Idempotent on external_uid: repeated syncs of the same contact (stable
    # "contact:<deviceId>:<contactId>") must NEVER create duplicates. If a row
    # with this external_uid already exists in this calendar, update it in place
    # instead of inserting a new one. Enforced server-side, so the client can
    # never duplicate — even without the reconcile read.
    existing = None
    if data.external_uid:
        existing = (
            db.query(models.LocalEvent)
            .filter(
                models.LocalEvent.calendar_id == cal.id,
                models.LocalEvent.external_uid == data.external_uid,
            )
            .first()
        )

    reminders = ",".join(str(m) for m in data.reminders) if data.reminders else None
    if existing is not None:
        ev = existing
        ev.title = data.title
        ev.start = data.start
        ev.end = data.end
        ev.all_day = data.allDay
        ev.location = data.location
        ev.description = data.description
        ev.color = data.color
        ev.rrule = data.rrule
        ev.is_private = data.private
        ev.reminders = reminders
        ev.birth_year = data.birth_year
    else:
        ev = models.LocalEvent(
            calendar_id=cal.id,
            uid=str(uuid.uuid4()),
            title=data.title,
            start=data.start,
            end=data.end,
            all_day=data.allDay,
            location=data.location,
            description=data.description,
            color=data.color,
            rrule=data.rrule,
            is_private=data.private,
            reminders=reminders,
            external_uid=data.external_uid,
            birth_year=data.birth_year,
            creator_id=current_user.id,  # server-side, never from the client
        )
        db.add(ev)
    dav_util.bump_dav(cal, ev)
    db.commit()
    db.refresh(ev)
    return _event_dict(ev, cal, db)


def _writable_event(db: Session, current_user: models.User, uid: str) -> models.LocalEvent:
    ev = db.query(models.LocalEvent).filter(models.LocalEvent.uid == uid).first()
    if not ev:
        raise HTTPException(404, "Event not found")
    # Raises 404/403 unless the user may write this event's calendar.
    permissions.accessible_local_calendar(db, current_user, ev.calendar_id, require_write=True)
    return ev


@router.put("/events/{uid}")
def update_event(
    uid: str,
    data: EventUpdate,
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    ev = _writable_event(db, current_user, uid)
    if data.private is not None:
        ev.is_private = data.private
    if data.title is not None:
        ev.title = data.title
    if data.start is not None:
        ev.start = data.start
    if data.end is not None:
        ev.end = data.end
    if data.allDay is not None:
        ev.all_day = data.allDay
    if data.location is not None:
        ev.location = data.location
    if data.description is not None:
        ev.description = data.description
    if data.color is not None:
        ev.color = data.color
    if data.rrule is not None:
        ev.rrule = data.rrule if data.rrule else None
    if data.exdate is not None:
        existing = ev.exdate or ""
        dates = [d for d in existing.split(",") if d]
        if data.exdate not in dates:
            dates.append(data.exdate)
        ev.exdate = ",".join(dates)
    if data.reminders is not None:
        ev.reminders = ",".join(str(m) for m in data.reminders) if data.reminders else None
    if data.external_uid is not None:
        ev.external_uid = data.external_uid
    if data.birth_year is not None:
        # -1 is the client's sentinel for "clear" (year became unknown).
        ev.birth_year = None if data.birth_year < 0 else data.birth_year
    dav_util.bump_dav(ev.calendar, ev)
    db.commit()
    return {"ok": True}


@router.delete("/events/{uid}")
def delete_event(
    uid: str,
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    ev = _writable_event(db, current_user, uid)
    dav_util.bump_dav(ev.calendar)
    db.delete(ev)
    db.commit()
    return {"ok": True}


@router.get("/calendars/{calendar_id}/birthdays")
def list_birthday_entries(
    calendar_id: int,
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    """Raw (unexpanded) rows of a birthday calendar so a client importer can
    reconcile against the address book by ``external_uid``. Contact-sourced rows
    carry an ``external_uid``; manually added birthdays have ``None`` and must be
    left untouched by the importer."""
    cal = permissions.accessible_local_calendar(db, current_user, calendar_id, require_write=True)
    events = (
        db.query(models.LocalEvent)
        .filter(models.LocalEvent.calendar_id == cal.id)
        .all()
    )
    out = []
    for ev in events:
        month = day = None
        try:
            parts = (ev.start or "")[:10].split("-")
            if len(parts) == 3:
                month, day = int(parts[1]), int(parts[2])
        except (ValueError, IndexError):
            pass
        out.append({
            "uid": ev.uid,
            "external_uid": ev.external_uid,
            "title": ev.title,
            "month": month,
            "day": day,
            "birth_year": ev.birth_year,
        })
    return out


# ── Sharing (owner only) ──────────────────────────────────

@router.get("/calendars/{calendar_id}/shares")
def list_shares(
    calendar_id: int,
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    permissions.is_calendar_owner(db, current_user, calendar_id)
    shares = (
        db.query(models.CalendarShare)
        .filter(models.CalendarShare.calendar_id == calendar_id)
        .all()
    )
    out = []
    for s in shares:
        u = db.query(models.User).filter(models.User.id == s.user_id).first()
        out.append({
            "user_id": s.user_id,
            "display_name": (u.display_name or u.username) if u else None,
            "permission": s.permission,
            "created_at": s.created_at,
        })
    return out


@router.post("/calendars/{calendar_id}/shares")
def add_share(
    calendar_id: int,
    data: ShareCreate,
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    permissions.is_calendar_owner(db, current_user, calendar_id)
    if data.permission not in ("read", "read_write"):
        raise HTTPException(422, "permission must be 'read' or 'read_write'")
    target = db.query(models.User).filter(models.User.id == data.user_id).first()
    if not target:
        raise HTTPException(404, "User not found")
    if target.id == current_user.id:
        raise HTTPException(422, "Cannot share a calendar with yourself")

    share = (
        db.query(models.CalendarShare)
        .filter(
            models.CalendarShare.calendar_id == calendar_id,
            models.CalendarShare.user_id == data.user_id,
        )
        .first()
    )
    if share:
        share.permission = data.permission  # update existing
    else:
        share = models.CalendarShare(
            calendar_id=calendar_id,
            user_id=data.user_id,
            permission=data.permission,
            created_at=_now_iso(),
        )
        db.add(share)
    db.commit()
    return {"ok": True}


@router.delete("/calendars/{calendar_id}/shares/{user_id}")
def remove_share(
    calendar_id: int,
    user_id: int,
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    permissions.is_calendar_owner(db, current_user, calendar_id)
    share = (
        db.query(models.CalendarShare)
        .filter(
            models.CalendarShare.calendar_id == calendar_id,
            models.CalendarShare.user_id == user_id,
        )
        .first()
    )
    if not share:
        raise HTTPException(404, "Share not found")
    db.delete(share)
    db.commit()
    return {"ok": True}


# ── iCal Import / Export (local calendars only) ───────────

def _import_ics_into(cal: models.LocalCalendar, raw: bytes, db: Session) -> dict:
    parsed = ical_io.parse_ics(raw)
    imported = 0
    skipped = 0
    errors = list(parsed["errors"])
    # local_events.uid is globally unique. Dedupe against the DB AND within this
    # file — e.g. Nextcloud exports recurring events as several VEVENTs sharing a
    # UID (RECURRENCE-ID overrides), which would otherwise violate the constraint.
    seen_uids: set[str] = set()
    for item in parsed["events"]:
        uid = item.get("uid") or str(uuid.uuid4())
        if uid in seen_uids:
            skipped += 1
            continue
        seen_uids.add(uid)
        existing = db.query(models.LocalEvent).filter(models.LocalEvent.uid == uid).first()
        if existing:
            skipped += 1
            continue
        ev = models.LocalEvent(
            calendar_id=cal.id,
            uid=uid,
            title=item.get("title") or "(ohne Titel)",
            start=item["start"],
            end=item["end"],
            all_day=item.get("all_day", False),
            location=item.get("location"),
            description=item.get("description"),
            rrule=item.get("rrule"),
            exdate=item.get("exdate"),
            creator_name_external=item.get("organizer"),
            etag=dav_util.new_tag(),
        )
        db.add(ev)
        imported += 1
    if imported:
        dav_util.bump_dav(cal)
    try:
        db.commit()
    except Exception as exc:
        db.rollback()
        raise ValueError(f"Import fehlgeschlagen: {exc}")
    return {"imported": imported, "skipped": skipped, "errors": errors}


# Cap .ics uploads so a huge file can't exhaust memory (read fully into RAM).
MAX_ICS_BYTES = 5 * 1024 * 1024  # 5 MB — generous for calendars


async def _read_capped(file: UploadFile) -> bytes:
    raw = await file.read(MAX_ICS_BYTES + 1)
    if len(raw) > MAX_ICS_BYTES:
        raise HTTPException(413, "Datei zu groß (max. 5 MB)")
    return raw


@router.post("/calendars/{calendar_id}/import")
async def import_calendar(
    calendar_id: int,
    file: UploadFile = File(...),
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    cal = permissions.accessible_local_calendar(db, current_user, calendar_id, require_write=True)
    raw = await _read_capped(file)
    try:
        return _import_ics_into(cal, raw, db)
    except ValueError as e:
        raise HTTPException(422, str(e))


@router.post("/import")
async def import_generic(
    file: UploadFile = File(...),
    calendar_id: Optional[int] = Form(None),
    create_calendar: bool = Form(False),
    calendar_name: Optional[str] = Form(None),
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    # Read (capped) first so an oversized upload can't leave an empty calendar.
    raw = await _read_capped(file)
    if create_calendar:
        cal = models.LocalCalendar(
            user_id=current_user.id,
            name=(calendar_name or "Importiert")[:120],
        )
        db.add(cal)
        db.commit()
        db.refresh(cal)
    elif calendar_id is not None:
        cal = permissions.accessible_local_calendar(db, current_user, calendar_id, require_write=True)
    else:
        raise HTTPException(422, "Provide calendar_id or create_calendar=true")

    try:
        result = _import_ics_into(cal, raw, db)
    except ValueError as e:
        raise HTTPException(422, str(e))
    result["calendar_id"] = cal.id
    return result


@router.get("/calendars/{calendar_id}/export")
def export_calendar(
    calendar_id: int,
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    cal = permissions.accessible_local_calendar(db, current_user, calendar_id)
    events = (
        db.query(models.LocalEvent)
        .filter(models.LocalEvent.calendar_id == cal.id)
        .all()
    )
    # Resolve creator display names for ORGANIZER.
    name_cache = {u.id: (u.display_name or u.username) for u in db.query(models.User).all()}
    ics = ical_io.build_ics(cal, events, name_cache=name_cache)
    safe_name = "".join(c for c in cal.name if c.isalnum() or c in (" ", "-", "_")).strip() or "calendar"
    return Response(
        content=ics,
        media_type="text/calendar",
        headers={"Content-Disposition": f'attachment; filename="{safe_name}.ics"'},
    )