"""GET /api/customers — paginated, filterable customer list.

Read-only query over the mirrored ``customer`` table. Supports filtering by
``channel``, ``owner_account_id``, ``user_id``, ``add_time_since`` and
``last_chat_since`` (direct columns) and ``department_id`` (resolved through
``customer.user_id`` -> ``staff.dept_id``). Results are ordered by
``last_chat_time desc`` (nulls last) then ``friend_id`` so the
most-recently-active contacts surface first.
"""

from __future__ import annotations

from typing import Annotated

import sqlalchemy as sa
from fastapi import APIRouter, Depends, Query
from sqlalchemy.ext.asyncio import AsyncSession

from app.api.deps import get_session
from app.api.schemas import CustomerOut, Page
from app.db.models import Customer, Staff

router = APIRouter(prefix="/api", tags=["customers"])

SessionDep = Annotated[AsyncSession, Depends(get_session)]
PageParam = Annotated[int, Query(ge=1)]
PageSizeParam = Annotated[int, Query(ge=1, le=100)]


@router.get("/customers")
async def list_customers(
    session: SessionDep,
    page: PageParam = 1,
    page_size: PageSizeParam = 20,
    channel: Annotated[str | None, Query()] = None,
    department_id: Annotated[str | None, Query()] = None,
    owner_account_id: Annotated[str | None, Query()] = None,
    user_id: Annotated[str | None, Query()] = None,
    add_time_since: Annotated[int | None, Query(ge=0)] = None,
    last_chat_since: Annotated[int | None, Query(ge=0)] = None,
) -> Page[CustomerOut]:
    """List customers with optional filters and pagination."""
    conditions = []
    if channel is not None:
        conditions.append(Customer.channel == channel)
    if owner_account_id is not None:
        conditions.append(Customer.owner_account_id == owner_account_id)
    if department_id is not None:
        # Customer has no dept column; resolve via the owning staff member.
        dept_user_ids = sa.select(Staff.user_id).where(
            Staff.dept_id == department_id
        )
        conditions.append(Customer.user_id.in_(dept_user_ids))
    if user_id is not None:
        conditions.append(Customer.user_id == user_id)
    if add_time_since is not None:
        conditions.append(Customer.add_time >= add_time_since)
    if last_chat_since is not None:
        conditions.append(Customer.last_chat_time >= last_chat_since)

    total_stmt = sa.select(sa.func.count()).select_from(Customer)
    if conditions:
        total_stmt = total_stmt.where(*conditions)
    total = (await session.execute(total_stmt)).scalar_one()

    list_stmt = sa.select(Customer)
    if conditions:
        list_stmt = list_stmt.where(*conditions)
    list_stmt = (
        list_stmt.order_by(
            sa.nullslast(Customer.last_chat_time.desc()),
            Customer.friend_id.asc(),
        )
        .limit(page_size)
        .offset((page - 1) * page_size)
    )

    rows = (await session.execute(list_stmt)).scalars().all()
    items = [CustomerOut.model_validate(row) for row in rows]
    return Page(items=items, total=total, page=page, page_size=page_size)