from fastapi import APIRouter, Depends, HTTPException, Path, Query
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy import select, or_
from sqlalchemy.orm import selectinload
from datetime import datetime, timezone
from typing import Optional, List

from app.database import get_db
from app.models.person import Person
from app.models.settings import Settings
from app.models.user import User
from app.models.user_connection import UserConnection
from app.schemas.person import PersonCreate, PersonUpdate, PersonResponse
from app.routers.auth import get_current_user
from app.services.connection import detach_umbral_contact, resolve_shared_profile

router = APIRouter()


def _compute_display_name(
    first_name: Optional[str],
    last_name: Optional[str],
    nickname: Optional[str],
    name: Optional[str],
) -> str:
    """Denormalise a display name. Nickname wins; else 'First Last'; else legacy name; else empty."""
    if nickname:
        return nickname
    full = ((first_name or '') + ' ' + (last_name or '')).strip()
    if full:
        return full
    # Don't fall back to stale `name` if all fields were explicitly cleared
    return (name or '').strip() if name else ''


@router.get("/", response_model=List[PersonResponse])
async def get_people(
    search: Optional[str] = Query(None),
    category: Optional[str] = Query(None),
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user)
):
    """Get all people with optional search and category filter."""
    query = select(Person).where(Person.user_id == current_user.id)

    if search:
        term = f"%{search}%"
        query = query.where(
            or_(
                Person.name.ilike(term),
                Person.first_name.ilike(term),
                Person.last_name.ilike(term),
                Person.nickname.ilike(term),
                Person.email.ilike(term),
                Person.company.ilike(term),
            )
        )
    if category:
        query = query.where(Person.category == category)

    query = query.order_by(Person.name.asc())

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

    # Batch-load shared profiles for umbral contacts
    umbral_people = [p for p in people if p.linked_user_id is not None]
    if umbral_people:
        linked_user_ids = [p.linked_user_id for p in umbral_people]

        # Batch fetch users and settings
        users_result = await db.execute(
            select(User).where(User.id.in_(linked_user_ids))
        )
        users_by_id = {u.id: u for u in users_result.scalars().all()}

        settings_result = await db.execute(
            select(Settings).where(Settings.user_id.in_(linked_user_ids))
        )
        settings_by_user = {s.user_id: s for s in settings_result.scalars().all()}

        # Batch fetch connection overrides
        conns_result = await db.execute(
            select(UserConnection).where(
                UserConnection.user_id == current_user.id,
                UserConnection.connected_user_id.in_(linked_user_ids),
            )
        )
        overrides_by_user = {
            c.connected_user_id: c.sharing_overrides
            for c in conns_result.scalars().all()
        }

        # Build shared profiles
        shared_profiles: dict[int, dict] = {}
        for uid in linked_user_ids:
            user = users_by_id.get(uid)
            user_settings = settings_by_user.get(uid)
            if user and user_settings:
                shared_profiles[uid] = resolve_shared_profile(
                    user, user_settings, overrides_by_user.get(uid)
                )
                # umbral_name is always visible (public identity), not a shareable field
                shared_profiles[uid]["umbral_name"] = user.umbral_name

        # Attach to response
        responses = []
        for p in people:
            resp = PersonResponse.model_validate(p)
            if p.linked_user_id and p.linked_user_id in shared_profiles:
                resp.shared_fields = shared_profiles[p.linked_user_id]
            responses.append(resp)
        return responses

    return people


@router.post("/", response_model=PersonResponse, status_code=201)
async def create_person(
    person: PersonCreate,
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user)
):
    """Create a new person with denormalised display name."""
    data = person.model_dump()
    # Auto-split legacy name into first/last if only name is provided
    if data.get('name') and not data.get('first_name') and not data.get('last_name') and not data.get('nickname'):
        parts = data['name'].split(' ', 1)
        data['first_name'] = parts[0]
        data['last_name'] = parts[1] if len(parts) > 1 else None
    new_person = Person(**data, user_id=current_user.id)
    new_person.name = _compute_display_name(
        new_person.first_name,
        new_person.last_name,
        new_person.nickname,
        new_person.name,
    )
    db.add(new_person)
    await db.commit()
    await db.refresh(new_person)

    return new_person


@router.get("/{person_id}", response_model=PersonResponse)
async def get_person(
    person_id: int = Path(ge=1, le=2147483647),
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user)
):
    """Get a specific person by ID."""
    result = await db.execute(
        select(Person).where(Person.id == person_id, Person.user_id == current_user.id)
    )
    person = result.scalar_one_or_none()

    if not person:
        raise HTTPException(status_code=404, detail="Person not found")

    resp = PersonResponse.model_validate(person)
    if person.linked_user_id:
        linked_user_result = await db.execute(
            select(User).where(User.id == person.linked_user_id)
        )
        linked_user = linked_user_result.scalar_one_or_none()
        linked_settings_result = await db.execute(
            select(Settings).where(Settings.user_id == person.linked_user_id)
        )
        linked_settings = linked_settings_result.scalar_one_or_none()
        conn_result = await db.execute(
            select(UserConnection).where(
                UserConnection.user_id == current_user.id,
                UserConnection.connected_user_id == person.linked_user_id,
            )
        )
        conn = conn_result.scalar_one_or_none()
        if linked_user and linked_settings:
            resp.shared_fields = resolve_shared_profile(
                linked_user, linked_settings, conn.sharing_overrides if conn else None
            )
            resp.shared_fields["umbral_name"] = linked_user.umbral_name
    return resp


@router.put("/{person_id}", response_model=PersonResponse)
async def update_person(
    person_id: int = Path(ge=1, le=2147483647),
    person_update: PersonUpdate = ...,
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user)
):
    """Update a person and refresh the denormalised display name."""
    result = await db.execute(
        select(Person).where(Person.id == person_id, Person.user_id == current_user.id)
    )
    person = result.scalar_one_or_none()

    if not person:
        raise HTTPException(status_code=404, detail="Person not found")

    update_data = person_update.model_dump(exclude_unset=True)

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

    # Recompute display name after applying updates
    person.name = _compute_display_name(
        person.first_name,
        person.last_name,
        person.nickname,
        person.name,
    )
    # Guarantee timestamp refresh regardless of DB driver behaviour
    person.updated_at = datetime.now(timezone.utc).replace(tzinfo=None)

    await db.commit()
    await db.refresh(person)

    return person


async def _sever_connection(db: AsyncSession, current_user: User, person: Person) -> None:
    """Remove bidirectional UserConnection rows and detach the counterpart's Person."""
    if not person.linked_user_id:
        return

    counterpart_id = person.linked_user_id

    # Find our connection
    conn_result = await db.execute(
        select(UserConnection).where(
            UserConnection.user_id == current_user.id,
            UserConnection.connected_user_id == counterpart_id,
        )
    )
    our_conn = conn_result.scalar_one_or_none()

    # Find reverse connection
    reverse_result = await db.execute(
        select(UserConnection).where(
            UserConnection.user_id == counterpart_id,
            UserConnection.connected_user_id == current_user.id,
        )
    )
    reverse_conn = reverse_result.scalar_one_or_none()

    # Detach the counterpart's Person record (if it exists)
    if reverse_conn and reverse_conn.person_id:
        cp_result = await db.execute(
            select(Person).where(Person.id == reverse_conn.person_id)
        )
        cp_person = cp_result.scalar_one_or_none()
        if cp_person:
            await detach_umbral_contact(cp_person)

    # Delete both connection rows
    if our_conn:
        await db.delete(our_conn)
    if reverse_conn:
        await db.delete(reverse_conn)


@router.put("/{person_id}/unlink", response_model=PersonResponse)
async def unlink_person(
    person_id: int = Path(ge=1, le=2147483647),
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user)
):
    """Unlink an umbral contact — convert to standard contact and sever the connection."""
    result = await db.execute(
        select(Person).where(Person.id == person_id, Person.user_id == current_user.id)
    )
    person = result.scalar_one_or_none()

    if not person:
        raise HTTPException(status_code=404, detail="Person not found")
    if not person.is_umbral_contact:
        raise HTTPException(status_code=400, detail="Person is not an umbral contact")

    await _sever_connection(db, current_user, person)
    await detach_umbral_contact(person)

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


@router.delete("/{person_id}", status_code=204)
async def delete_person(
    person_id: int = Path(ge=1, le=2147483647),
    db: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_current_user)
):
    """Delete a person. If umbral contact, also severs the bidirectional connection."""
    result = await db.execute(
        select(Person).where(Person.id == person_id, Person.user_id == current_user.id)
    )
    person = result.scalar_one_or_none()

    if not person:
        raise HTTPException(status_code=404, detail="Person not found")

    if person.is_umbral_contact:
        await _sever_connection(db, current_user, person)

    await db.delete(person)
    await db.commit()

    return None