tgit/app/access/service.py

"""Invites, members and revocation (SPEC §3.1, ADR-011)."""

import hashlib
import secrets
from collections.abc import Callable
from dataclasses import dataclass
from datetime import UTC, datetime, timedelta
from enum import StrEnum
from typing import Any, cast

from sqlalchemy import CursorResult, delete, func, select, update

from app.config import AccessSettings
from app.db.models import AccessAttempt, Draft, FsmState, Invite, Role, User, utcnow
from app.db.session import SessionMaker

LAST_SEEN_EVERY = timedelta(minutes=5)
ATTEMPT_WINDOW = timedelta(hours=1)


class RedeemStatus(StrEnum):
    OK = "ok"
    ALREADY_MEMBER = "already_member"
    REJECTED = "rejected"  # unknown, used or expired — one answer, no hints which tokens existed
    THROTTLED = "throttled"


@dataclass(frozen=True)
class TgUser:
    tg_id: int
    full_name: str
    username: str | None = None


@dataclass(frozen=True)
class CreatedInvite:
    token: str
    expires_at: datetime


def hash_token(token: str) -> str:
    return hashlib.sha256(token.encode()).hexdigest()


class AccessService:
    def __init__(self, sessions: SessionMaker, settings: AccessSettings, clock: Callable[[], datetime] = utcnow):
        self._sessions = sessions
        self._settings = settings
        self._clock = clock

    async def bootstrap_admins(self) -> None:
        """ADMIN_IDS become active admins in the DB; everybody else gets in only by invite (SPEC A-8)."""
        async with self._sessions.begin() as s:
            for tg_id in self._settings.admin_ids:
                user = await s.get(User, tg_id)
                if user is None:
                    s.add(User(tg_id=tg_id, full_name=f"admin {tg_id}", role=Role.ADMIN, joined_at=self._clock()))
                else:
                    user.role, user.is_active = Role.ADMIN, True

    async def get_member(self, tg_id: int) -> User | None:
        async with self._sessions() as s:
            user = await s.get(User, tg_id)
            return user if user is not None and user.is_active else None

    async def touch(self, member: User, seen: TgUser) -> None:
        """Refresh name and last-seen, at most every few minutes — not a write per update."""
        now = self._clock()
        last = member.last_seen_at
        if (
            last is not None
            and now - _aware(last) < LAST_SEEN_EVERY
            and (member.full_name, member.username) == (seen.full_name, seen.username)
        ):
            return
        async with self._sessions.begin() as s:
            await s.execute(
                update(User)
                .where(User.tg_id == member.tg_id)
                .values(last_seen_at=now, full_name=seen.full_name, username=seen.username)
            )

    async def create_invite(self, admin_id: int) -> CreatedInvite:
        token = secrets.token_urlsafe(16)  # 128 bits, 22 chars of [A-Za-z0-9_-]: fits the 64-char deep link payload
        expires_at = self._clock() + timedelta(hours=self._settings.invite_ttl_hours)
        async with self._sessions.begin() as s:
            s.add(
                Invite(
                    token_hash=hash_token(token), created_by=admin_id, created_at=self._clock(), expires_at=expires_at
                )
            )
        return CreatedInvite(token=token, expires_at=expires_at)

    async def redeem(self, token: str, who: TgUser) -> RedeemStatus:
        now = self._clock()
        try:
            async with self._sessions.begin() as s:
                existing = await s.get(User, who.tg_id)
                if existing is not None and existing.is_active:
                    return RedeemStatus.ALREADY_MEMBER
                failed = await s.scalar(
                    select(func.count())
                    .select_from(AccessAttempt)
                    .where(
                        AccessAttempt.tg_id == who.tg_id,
                        AccessAttempt.ok.is_(False),
                        AccessAttempt.at > now - ATTEMPT_WINDOW,
                    )
                )
                if (failed or 0) >= self._settings.max_failed_attempts:
                    return RedeemStatus.THROTTLED

                invite = await s.scalar(select(Invite).where(Invite.token_hash == hash_token(token)))
                if invite is None or invite.used_by is not None or _aware(invite.expires_at) <= now:
                    raise _Rejected

                if existing is None:
                    s.add(
                        User(
                            tg_id=who.tg_id,
                            full_name=who.full_name,
                            username=who.username,
                            role=Role.MEMBER,
                            invited_by=invite.created_by,
                            joined_at=now,
                            last_seen_at=now,
                        )
                    )
                else:  # revoked earlier, invited again
                    existing.is_active, existing.role, existing.invited_by = True, Role.MEMBER, invite.created_by
                    existing.full_name, existing.username, existing.last_seen_at = who.full_name, who.username, now
                await s.flush()  # the user row must exist before invites.used_by points at it

                # Claim atomically: of two people scanning the same QR only one UPDATE matches the row,
                # the loser's transaction (with its freshly created user) is rolled back.
                result = await s.execute(
                    update(Invite)
                    .where(Invite.id == invite.id, Invite.used_by.is_(None))
                    .values(used_by=who.tg_id, used_at=now)
                )
                if cast(CursorResult[Any], result).rowcount != 1:
                    raise _Rejected
                s.add(AccessAttempt(tg_id=who.tg_id, at=now, ok=True))
        except _Rejected:
            async with self._sessions.begin() as s:
                s.add(AccessAttempt(tg_id=who.tg_id, at=now, ok=False))
            return RedeemStatus.REJECTED
        return RedeemStatus.OK

    async def list_members(self) -> list[User]:
        async with self._sessions() as s:
            rows = await s.scalars(select(User).where(User.is_active.is_(True)).order_by(User.role, User.joined_at))
            return list(rows)

    async def revoke(self, tg_id: int) -> bool:
        """Cut a member off at once: their updates are ignored from now on, draft and dialog state are dropped."""
        async with self._sessions.begin() as s:
            user = await s.get(User, tg_id)
            if user is None or not user.is_active or user.role is Role.ADMIN:
                return False
            user.is_active = False
            await s.execute(delete(Draft).where(Draft.user_id == tg_id))
            # FSM keys are "bot:chat:user:…"; in a private chat chat == user
            await s.execute(delete(FsmState).where(FsmState.key.like(f"%:{tg_id}:{tg_id}:%")))
        return True


class _Rejected(Exception):
    pass


def _aware(value: datetime) -> datetime:
    # SQLite hands back naive datetimes even for timezone=True columns; everything we store is UTC.
    return value if value.tzinfo is not None else value.replace(tzinfo=UTC)