"""Recipient autocomplete from known_recipients (SPEC §9.1, §4).

Prefix match on email or name, ranked by ``times_used`` decayed by recency. The
composer merges these with plugin capability providers client-side (M3).
"""

from __future__ import annotations

from typing import Annotated

from fastapi import APIRouter, Depends, Query
from pydantic import BaseModel
from sqlalchemy import func, select
from sqlalchemy.ext.asyncio import AsyncSession

from app.db import get_session
from app.identity.deps import CurrentUser
from app.models import KnownRecipient

router = APIRouter(prefix="/recipients", tags=["compose"])

DbSession = Annotated[AsyncSession, Depends(get_session)]


class Suggestion(BaseModel):
    name: str
    email: str


@router.get("/suggest", response_model=list[Suggestion])
async def suggest(
    user: CurrentUser, db: DbSession, q: str = Query("", max_length=200)
) -> list[Suggestion]:
    term = q.strip()
    if not term:
        return []
    like = f"{term}%"
    # Recency-decayed score: times_used / (1 + age_in_days). Ranks frequent and
    # recent correspondents ahead of stale ones (SPEC §9.1).
    age_days = func.extract("epoch", func.now() - KnownRecipient.last_used_at) / 86400.0
    score = KnownRecipient.times_used / (1.0 + age_days)
    stmt = (
        select(KnownRecipient.name, KnownRecipient.email)
        .where(
            KnownRecipient.user_id == user.id,
            KnownRecipient.email.ilike(like) | KnownRecipient.name.ilike(like),
        )
        .order_by(score.desc())
        .limit(10)
    )
    rows = (await db.execute(stmt)).all()
    return [Suggestion(name=row.name, email=row.email) for row in rows]