import logging
import secrets
from datetime import datetime, timedelta

from fastapi import APIRouter, Depends, HTTPException, BackgroundTasks, status, Request
from sqlalchemy.orm import Session

from app.services import captcha, refresh_tokens, site_settings
from app.database import get_db
from app.models.user import User
from app.models.email_verification import EmailVerification
from app.models.password_reset import PasswordReset
from app.schemas.auth import (
    UserCreate, UserResponse, Token, LoginRequest, LogoutRequest, RefreshRequest,
    UserUpdateMe, ForgotPasswordRequest, ResetPasswordRequest, SsoExchangeRequest,
)
from app.services import email_service
from app.utils.auth import (
    check_rate_limit, get_password_hash, verify_password, create_access_token,
    get_current_user,
)

logger = logging.getLogger(__name__)
router = APIRouter()


def _login_key(client_ip: str) -> str:
    return f"login_attempts:{client_ip}"


def _check_login_rate_limit(client_ip: str):
    """How many times an address may guess, before it has to wait.

    Counted per address and cleared by a success, because what this is for is
    guessing — and somebody who signs in correctly has not guessed. Counting
    successes too would lock out a hospital: one public address, a ward full of
    people, eleven of whom happened to open the app this afternoon.
    """
    try:
        import redis as redis_lib
        from app.config import settings
        r = redis_lib.from_url(settings.REDIS_URL, decode_responses=True, socket_connect_timeout=1)
        key = _login_key(client_ip)
        count = r.incr(key)
        if count == 1:
            r.expire(key, settings.LOGIN_WINDOW_MINUTES * 60)
        if count > settings.LOGIN_MAX_ATTEMPTS:
            raise HTTPException(
                status_code=429,
                detail=f"Too many login attempts. Try again in {settings.LOGIN_WINDOW_MINUTES} minutes.")
    except HTTPException:
        raise
    except Exception as e:
        import logging; logging.getLogger(__name__).warning(f"Redis rate limit unavailable (failing open): {e}")


def _clear_login_rate_limit(client_ip: str):
    """A correct password is the end of the matter."""
    try:
        import redis as redis_lib
        from app.config import settings
        redis_lib.from_url(settings.REDIS_URL, decode_responses=True,
                           socket_connect_timeout=1).delete(_login_key(client_ip))
    except Exception:
        pass


# Rate limit: max 3 reset requests per email per hour
RESET_LIMIT = 3
RESET_WINDOW_HOURS = 1


def _check_reset_rate_limit(db: Session, email: str):
    """Refuse a fourth request in an hour — for any address, not only a real one.

    Returning early for an unknown address made this the oracle the careful
    wording below exists to avoid: ask four times and a registered address
    answers 429 while an unknown one answers 200 for ever. The limit is now
    counted against the address as typed, so both answer the same.
    """
    email_normalized = email.lower().strip()
    user = db.query(User).filter(User.email == email_normalized).first()
    window_start = datetime.utcnow() - timedelta(hours=RESET_WINDOW_HOURS)
    if user is None:
        # No rows to count for an address with no account, so the attempts are
        # counted in Redis instead — keyed by a fingerprint, because a list of
        # addresses somebody tried is itself worth not keeping.
        import hashlib

        from app.utils.auth import check_rate_limit
        check_rate_limit(
            key=f"pwreset:{hashlib.sha256(email_normalized.encode()).hexdigest()}",
            max_calls=RESET_LIMIT, window_seconds=RESET_WINDOW_HOURS * 3600,
            detail="Too many reset requests. Please wait before trying again.")
        return
    count = db.query(PasswordReset).filter(
        PasswordReset.user_id == user.id,
        PasswordReset.created_at >= window_start,
    ).count()
    if count >= RESET_LIMIT:
        raise HTTPException(
            status_code=status.HTTP_429_TOO_MANY_REQUESTS,
            detail=f"Too many reset requests. Please wait before trying again.",
        )


@router.get("/signup-policy")
def signup_policy(db: Session = Depends(get_db)):
    """What a would-be member needs, before they are anybody.

    Unauthenticated on purpose: the registration form has to know whether to
    ask for a code, and it is asking before it has an account to ask with. It
    says only whether one is needed — never whether a given code is valid,
    which would turn this into somewhere to guess them.
    """
    # The very first account is always allowed, or a new install could lock
    # itself out before an administrator exists to issue a code.
    if db.query(User).count() == 0:
        return {"first_user": True, "registration_open": True}
    # Whether anyone may join at all, so the sign-in page can stop offering a
    # door that is locked. It was offering one: registration can be turned off
    # site-wide, and the only way to find out was to fill the form in and be
    # refused.
    # Single sign-on closes the password door, and this is the one question
    # the sign-up form already asks. Saying so here means the form can decline
    # to draw itself rather than collect a name, an email and a password
    # twice, and then be refused by the POST.
    from app.config import settings as cfg
    sso_only = _get_sso_settings()["sso_only"]
    return {"first_user": False,
            "sso_only": sso_only,
            # So the page can name the provider rather than say "single
            # sign-on" at somebody who only knows it as PedsHub SSO.
            "provider_name": (cfg.OIDC_PROVIDER_NAME
                              if cfg.OIDC_PROVIDER_URL and cfg.OIDC_CLIENT_ID else None),
            "registration_open": (not sso_only
                                  and site_settings.get_flag("registration_enabled"))}


@router.post("/register")
async def register(user_data: UserCreate, background_tasks: BackgroundTasks, db: Session = Depends(get_db)):
    _refuse_when_sso_only("Accounts are created through SSO on this site.")
    # Failing open: an hCaptcha outage should cost the site a little spam, not
    # every account that would have been created while it lasted.
    await captcha.require_human(user_data.captcha_token, fail_open=True)

    # Check if registration is enabled (unless this is the first user - always allow admin creation)
    is_first_user = db.query(User).count() == 0
    if not is_first_user:
        try:
            import redis as redis_lib
            from app.config import settings
            r = redis_lib.from_url(settings.REDIS_URL, decode_responses=True, socket_connect_timeout=1)
            registration_enabled = r.get("settings:registration_enabled")
            # Default to enabled if not set, disabled if explicitly set to "false"
            if registration_enabled == "false":
                raise HTTPException(status_code=403, detail="Registration is currently disabled by administrator")
        except HTTPException:
            raise
        except Exception as e:
            import logging; logging.getLogger(__name__).warning(f"Redis registration check failed (failing open): {e}")

    if len(user_data.password) < 8:
        raise HTTPException(status_code=400, detail="Password must be at least 8 characters")

    email_normalized = user_data.email.lower().strip()
    existing = db.query(User).filter(User.email == email_normalized).first()
    if existing:
        raise HTTPException(status_code=400, detail="Email already registered")
    user = User(
        email=email_normalized,
        hashed_password=get_password_hash(user_data.password),
        name=user_data.name,
        role="admin" if is_first_user else "user",
    )
    db.add(user)
    db.flush()

    # Create email verification record
    token = secrets.token_urlsafe(32)
    verification = EmailVerification(
        user_id=user.id,
        token=token,
        expires_at=datetime.utcnow() + timedelta(hours=24),
        verified_at=datetime.utcnow() if is_first_user else None,
    )
    db.add(verification)
    db.commit()
    db.refresh(user)

    if is_first_user:
        # Auto-verified admin — log them in immediately
        access_token = create_access_token(data={"sub": user.email})
        return {"access_token": access_token, "token_type": "bearer"}

    # Regular user — must verify email before logging in
    background_tasks.add_task(email_service.send_verification_email, user.email, user.name, token)
    return {"requires_verification": True, "message": "Account created. Please check your email to verify your account before logging in."}


@router.post("/login", response_model=Token)
async def login(login_data: LoginRequest, db: Session = Depends(get_db), request: Request = None):
    # Block password login if SSO-only mode
    sso_settings = _get_sso_settings()
    if sso_settings["sso_only"]:
        raise HTTPException(status_code=403, detail="Password login is disabled. Please use SSO.")

    client_ip = (request.client.host if request and request.client else "unknown")
    if request:
        _check_login_rate_limit(client_ip)

    email_normalized = login_data.email.lower().strip()
    user = db.query(User).filter(User.email == email_normalized).first()
    # An account with no password is not an account with the wrong password,
    # but it is told the same thing: which accounts have one is not a question
    # this endpoint answers.
    if not user or not user.hashed_password or not verify_password(
            login_data.password, user.hashed_password):
        raise HTTPException(status_code=401, detail="Invalid email or password")

    # Check email verification — skip for users without any verification record (legacy/seeded)
    verification = db.query(EmailVerification).filter(EmailVerification.user_id == user.id).first()
    if verification and verification.verified_at is None:
        raise HTTPException(
            status_code=403,
            detail="Email not verified. Please check your inbox and verify your email before logging in.",
        )

    _clear_login_rate_limit(client_ip)
    return _signed_in(db, user, login_data, request)


def _signed_in(db: Session, user: User, login_data: LoginRequest, request: Request | None) -> Token:
    """What a successful sign-in hands back.

    A browser gets what it always got. A client that says it wants a refresh
    token also gets one, because it has nowhere safe to keep a password and no
    person sitting in front of it to ask again.
    """
    # Imported here, as everywhere else in this file: a module-level `settings`
    # plus these function-level ones would make the name local to each of them
    # and blow up on first use.
    from app.config import settings
    token = Token(
        access_token=create_access_token(data={"sub": user.email}),
        expires_in=settings.ACCESS_TOKEN_EXPIRE_MINUTES * 60,
    )
    if login_data.refresh:
        token.refresh_token = refresh_tokens.issue(
            db, user, label=login_data.device,
            ip=request.client.host if request and request.client else None)
    return token


@router.post("/refresh", response_model=Token)
def refresh(data: RefreshRequest, db: Session = Depends(get_db), request: Request = None):
    """Trade a refresh token for a new pair.

    The old one is spent by this call. Presenting a spent token ends the whole
    session it belongs to: either it was copied or a client is replaying, and
    from here those look the same.
    """
    from app.config import settings
    client_ip = request.client.host if request and request.client else "unknown"
    # Flood protection, not a security control: the security here is that a
    # refresh token is 256 unguessable bits and spending one twice ends the
    # session. Generous, because an address can be a whole hospital behind one
    # NAT and every app launch refreshes.
    check_rate_limit(f"refresh:{client_ip}", settings.REFRESH_MAX_PER_HOUR, 3600,
                     "Too many refresh attempts. Try again later.")
    spent = refresh_tokens.spend(db, data.refresh_token, ip=client_ip)
    if spent is None:
        raise HTTPException(401, "That sign-in has expired. Sign in again.")
    user, rotated = spent
    verification = db.query(EmailVerification).filter(EmailVerification.user_id == user.id).first()
    if verification and verification.verified_at is None:
        raise HTTPException(403, "Email not verified.")
    return Token(
        access_token=create_access_token(data={"sub": user.email}),
        expires_in=settings.ACCESS_TOKEN_EXPIRE_MINUTES * 60,
        refresh_token=rotated,
    )


@router.post("/logout", status_code=204)
def logout(data: LogoutRequest, db: Session = Depends(get_db),
           current_user: User = Depends(get_current_user)):
    """End this session, or every session.

    An access token already issued is a signature and cannot be recalled; it
    dies of old age within the day. What this ends is the ability to get
    another one, which is what a lost phone actually needs.
    """
    if data.everywhere:
        refresh_tokens.revoke_all(db, current_user)
    elif data.refresh_token:
        refresh_tokens.revoke_one(db, data.refresh_token)


@router.get("/sessions")
def list_sessions(db: Session = Depends(get_db), current_user: User = Depends(get_current_user)):
    """Where this account is signed in, so a person can see and end them."""
    return refresh_tokens.sessions(db, current_user)


@router.delete("/sessions/{family}", status_code=204)
def end_session(family: str, db: Session = Depends(get_db),
                current_user: User = Depends(get_current_user)):
    refresh_tokens.revoke_family(db, current_user, family)


@router.get("/verify-email")
def verify_email(token: str, db: Session = Depends(get_db)):
    record = db.query(EmailVerification).filter(EmailVerification.token == token).first()
    if not record:
        raise HTTPException(status_code=400, detail="Invalid verification token")
    if record.verified_at is not None:
        return {"message": "Email already verified. You can log in."}
    if datetime.utcnow() > record.expires_at:
        raise HTTPException(status_code=400, detail="Verification link has expired. Please register again or request a new link.")

    record.verified_at = datetime.utcnow()
    db.commit()
    return {"message": "Email verified successfully! You can now log in."}


@router.post("/resend-verification")
async def resend_verification(data: ForgotPasswordRequest, background_tasks: BackgroundTasks, db: Session = Depends(get_db)):
    _refuse_when_sso_only("Accounts are created through SSO on this site.")
    email_normalized = data.email.lower().strip()
    user = db.query(User).filter(User.email == email_normalized).first()
    if not user:
        return {"message": "If that email exists, a verification link has been sent."}

    record = db.query(EmailVerification).filter(EmailVerification.user_id == user.id).first()
    if record and record.verified_at is not None:
        # The same sentence as every other outcome. Saying "already verified"
        # here told anybody who asked that the address has an account and that
        # it is in use — which is the whole of what the wording below is for.
        return {"message": "If that email exists, a verification link has been sent."}

    token = secrets.token_urlsafe(32)
    if record:
        record.token = token
        record.expires_at = datetime.utcnow() + timedelta(hours=24)
    else:
        db.add(EmailVerification(user_id=user.id, token=token, expires_at=datetime.utcnow() + timedelta(hours=24)))
    db.commit()

    background_tasks.add_task(email_service.send_verification_email, user.email, user.name, token)
    return {"message": "If that email exists, a verification link has been sent."}


@router.post("/forgot-password")
async def forgot_password(data: ForgotPasswordRequest, background_tasks: BackgroundTasks, db: Session = Depends(get_db)):
    _refuse_when_sso_only("There is no password to reset. Please use SSO.")
    email_normalized = data.email.lower().strip()
    _check_reset_rate_limit(db, email_normalized)

    user = db.query(User).filter(User.email == email_normalized).first()
    # Always return same message to avoid email enumeration
    if not user:
        return {"message": "If that email is registered, a reset link has been sent."}

    token = secrets.token_urlsafe(32)
    reset = PasswordReset(
        user_id=user.id,
        token=token,
        expires_at=datetime.utcnow() + timedelta(hours=1),
    )
    db.add(reset)
    db.commit()

    background_tasks.add_task(email_service.send_password_reset_email, user.email, user.name, token)
    return {"message": "If that email is registered, a reset link has been sent."}


@router.post("/reset-password")
def reset_password(data: ResetPasswordRequest, db: Session = Depends(get_db)):
    _refuse_when_sso_only("There is no password to reset. Please use SSO.")
    if len(data.new_password) < 8:
        raise HTTPException(status_code=400, detail="Password must be at least 8 characters")

    record = db.query(PasswordReset).filter(
        PasswordReset.token == data.token,
        PasswordReset.used == False,
    ).first()
    if not record:
        raise HTTPException(status_code=400, detail="Invalid or already used reset token")
    if datetime.utcnow() > record.expires_at:
        raise HTTPException(status_code=400, detail="Reset link has expired. Please request a new one.")

    user = db.query(User).filter(User.id == record.user_id).first()
    if not user:
        raise HTTPException(status_code=404, detail="User not found")

    user.hashed_password = get_password_hash(data.new_password)
    record.used = True
    db.commit()
    return {"message": "Password reset successfully. You can now log in."}


@router.get("/me/settings")
def get_user_settings(
    current_user: User = Depends(get_current_user),
    db: Session = Depends(get_db),
):
    """Get user settings. Most settings live in Redis (Nextcloud config etc.);
    reminders_disabled is canonical in Postgres and overrides Redis."""
    data = {}
    try:
        import redis as redis_lib, json
        from app.config import settings as cfg
        r = redis_lib.from_url(cfg.REDIS_URL, decode_responses=True)
        raw = r.get(f"user_settings:{current_user.id}")
        if raw:
            data = json.loads(raw)
    except Exception as e:
        import logging; logging.getLogger(__name__).warning(f"Failed to load user settings: {e}")

    # Canonical preferences come from the DB. Redis holds the rest, and a cache
    # is not where a choice somebody made once should live.
    data["reminders_disabled"] = bool(current_user.reminders_disabled)
    data["tts_voice"] = current_user.tts_voice
    return data


@router.put("/me/settings")
def save_user_settings(
    settings_data: dict,
    current_user: User = Depends(get_current_user),
    db: Session = Depends(get_db),
):
    """Save user settings. reminders_disabled is persisted to Postgres;
    other keys go to Redis."""
    # Persist opt-out preference to DB (canonical source for the scheduler)
    changed = False
    if "reminders_disabled" in settings_data:
        current_user.reminders_disabled = bool(settings_data.get("reminders_disabled"))
        changed = True
    if "tts_voice" in settings_data:
        voice = (settings_data.get("tts_voice") or "").strip()
        current_user.tts_voice = voice or None
        changed = True
    if changed:
        db.add(current_user)
        db.commit()

    # Keep the full blob in Redis so other fields (Nextcloud config etc.) persist
    try:
        import redis as redis_lib, json
        from app.config import settings as cfg
        r = redis_lib.from_url(cfg.REDIS_URL, decode_responses=True)
        r.set(f"user_settings:{current_user.id}", json.dumps(settings_data))
    except Exception as e:
        import logging; logging.getLogger(__name__).warning(f"Failed to save user settings to Redis: {e}")
    return {"saved": True}


@router.get("/me", response_model=UserResponse)
def get_me(current_user: User = Depends(get_current_user)):
    return UserResponse.of(current_user)


@router.put("/me")
def update_me(data: UserUpdateMe, db: Session = Depends(get_db), current_user: User = Depends(get_current_user)):
    if data.new_password:
        # Setting one is the same door. A password nobody can log in with is
        # not harmless: it is a credential waiting for the flag to be turned
        # off again.
        _refuse_when_sso_only("Passwords are not used on this site. Please use SSO.")
        # A first password is not a change of one. Somebody who signed in with
        # a code or through single sign-on has none to confirm, and asking for
        # it locked them out of ever setting one — the only way through was
        # "forgot password", which is a strange thing to click when you never
        # had one.
        if current_user.hashed_password:
            if not data.current_password:
                raise HTTPException(status_code=400, detail="Current password required to set a new one")
            if not verify_password(data.current_password, current_user.hashed_password):
                raise HTTPException(status_code=400, detail="Current password is incorrect")
        if len(data.new_password) < 8:
            raise HTTPException(status_code=400, detail="New password must be at least 8 characters")
        current_user.hashed_password = get_password_hash(data.new_password)

    if data.name:
        current_user.name = data.name

    db.commit()
    db.refresh(current_user)
    return {
        "id": current_user.id, "email": current_user.email,
        "name": current_user.name, "role": current_user.role,
    }


# ── SSO / OIDC ─────────────────────────────────────────────────────

def _get_sso_settings():
    """Return SSO admin settings from Redis."""
    try:
        import redis as redis_lib
        from app.config import settings as cfg
        r = redis_lib.from_url(cfg.REDIS_URL, decode_responses=True, socket_connect_timeout=1)
        return {
            "sso_only": r.get("settings:sso_only") == "true",
        }
    except Exception:
        return {"sso_only": False}


#: How long a one-time code is worth anything. The browser is mid-redirect and
#: spends it immediately; a minute is generous for that and short enough that a
#: code seen in a log is already dead.
SSO_CODE_TTL = 60


def _sso_store():
    import redis as redis_lib
    from app.config import settings as cfg
    return redis_lib.from_url(cfg.REDIS_URL, decode_responses=True, socket_connect_timeout=1)


def _stash_sso_token(token: str) -> str | None:
    """Park a freshly minted token behind a random code. None if Redis is away."""
    code = secrets.token_urlsafe(32)
    try:
        _sso_store().setex(f"sso:exchange:{code}", SSO_CODE_TTL, token)
        return code
    except Exception:
        return None


@router.post("/sso/exchange", response_model=Token)
def sso_exchange(data: SsoExchangeRequest):
    """Trade a one-time code for the token it stands for.

    Once. The key is deleted as it is read, so a code replayed from a log, a
    history entry or a Referer header buys nothing.
    """
    from app.config import settings as cfg

    key = f"sso:exchange:{data.code}"
    try:
        store = _sso_store()
        # GETDEL where the server has it, which is atomic and settles the race
        # between two tabs; the pipeline is the same thing for an older Redis.
        try:
            token = store.getdel(key)
        except Exception:
            pipe = store.pipeline()
            pipe.get(key)
            pipe.delete(key)
            token = pipe.execute()[0]
    except Exception:
        raise HTTPException(status_code=503, detail="Could not complete sign-in. Please try again.")
    if not token:
        raise HTTPException(status_code=400, detail="That sign-in link has expired. Please sign in again.")
    return Token(access_token=token, expires_in=cfg.ACCESS_TOKEN_EXPIRE_MINUTES * 60)


def _refuse_when_sso_only(what: str = "Password login is disabled. Please use SSO.") -> None:
    """No password door while the site is single sign-on.

    Login and the login codes checked this; register, forgot-password and
    reset-password did not. So with SSO-only on, somebody could still be
    issued a password account they could not use — and if the flag were ever
    turned off, that is a password account nobody vetted, sitting in the
    users table waiting.
    """
    if _get_sso_settings()["sso_only"]:
        raise HTTPException(status_code=403, detail=what)


@router.get("/sso/config")
def sso_config():
    """Public endpoint — tells frontend whether SSO is available and login mode."""
    from app.config import settings as cfg
    sso_enabled = bool(cfg.OIDC_PROVIDER_URL and cfg.OIDC_CLIENT_ID)
    sso_settings = _get_sso_settings()
    from app.services import sso_roles

    return {
        "sso_enabled": sso_enabled,
        "sso_only": sso_settings["sso_only"],
        "provider_name": cfg.OIDC_PROVIDER_NAME if sso_enabled else None,
        # Whether roles come from the provider's groups. Says only that they
        # do, never which groups — enough for the access page to stop offering
        # a control that can now only answer 409.
        "roles_from_provider": sso_roles.is_configured(cfg),
    }


@router.get("/sso/login")
async def sso_login(request: Request):
    """Redirect user to the OIDC provider for login.

    `async`, and the redirect awaited. Authlib's Starlette client is the async
    one — `authorize_redirect` hands back a coroutine — so a sync endpoint
    returned that coroutine to FastAPI, which tried to serialise it as a
    response body and answered 500: "'coroutine' object is not iterable". The
    button had never worked; nothing found it because nothing had SSO
    configured to click it with.
    """
    from authlib.integrations.starlette_client import OAuth
    from starlette.responses import RedirectResponse
    from app.config import settings as cfg

    if not cfg.OIDC_PROVIDER_URL or not cfg.OIDC_CLIENT_ID:
        raise HTTPException(status_code=400, detail="SSO is not configured")

    oauth = OAuth()
    oauth.register(
        name="oidc",
        server_metadata_url=f"{cfg.OIDC_PROVIDER_URL.rstrip('/')}/.well-known/openid-configuration",
        client_id=cfg.OIDC_CLIENT_ID,
        client_secret=cfg.OIDC_CLIENT_SECRET,
        client_kwargs={"scope": cfg.OIDC_SCOPES},
    )

    redirect_uri = f"{cfg.APP_URL}/api/auth/sso/callback"
    return await oauth.oidc.authorize_redirect(request, redirect_uri)


@router.get("/sso/callback")
async def sso_callback(request: Request, db: Session = Depends(get_db)):
    """Handle OIDC provider callback — create or login user."""
    from authlib.integrations.starlette_client import OAuth
    from starlette.responses import RedirectResponse
    from app.config import settings as cfg
    from app.services import sso_roles

    if not cfg.OIDC_PROVIDER_URL or not cfg.OIDC_CLIENT_ID:
        raise HTTPException(status_code=400, detail="SSO is not configured")

    oauth = OAuth()
    oauth.register(
        name="oidc",
        server_metadata_url=f"{cfg.OIDC_PROVIDER_URL.rstrip('/')}/.well-known/openid-configuration",
        client_id=cfg.OIDC_CLIENT_ID,
        client_secret=cfg.OIDC_CLIENT_SECRET,
        client_kwargs={"scope": cfg.OIDC_SCOPES},
    )

    try:
        token = await oauth.oidc.authorize_access_token(request)
    except Exception:
        return RedirectResponse(url=f"{cfg.APP_URL}/login?error=sso_failed")

    userinfo = token.get("userinfo") or {}
    email = userinfo.get("email", "").lower().strip()
    name = userinfo.get("name") or userinfo.get("preferred_username") or email.split("@")[0]

    if not email:
        return RedirectResponse(url=f"{cfg.APP_URL}/login?error=no_email")

    # An address the provider will not vouch for is not an identity. Matching
    # on email means whoever proves an address owns the account that already
    # uses it, so an unverified claim would hand over an existing account to
    # anybody who typed the address into a provider that does not check. Only
    # refused when the provider says so explicitly: a provider that omits the
    # claim is not asserting the address is unverified.
    if userinfo.get("email_verified") is False:
        return RedirectResponse(url=f"{cfg.APP_URL}/login?error=email_unverified")

    # Find or create user
    user = db.query(User).filter(User.email == email).first()
    if not user:
        user = User(
            email=email,
            # No password rather than one nobody knows. A random string here
            # reads as "has a password" everywhere that asks.
            hashed_password=None,
            name=name,
            role="user",
        )
        db.add(user)
        db.flush()
        # Auto-verify SSO users
        verification = EmailVerification(
            user_id=user.id,
            token=secrets.token_urlsafe(32),
            expires_at=datetime.utcnow() + timedelta(hours=1),
            verified_at=datetime.utcnow(),
        )
        db.add(verification)
        db.commit()
        db.refresh(user)

    # The provider's directory decides what they are here, when it has been
    # told to. Applied on every sign-in rather than only at creation: a list
    # that can add somebody to the educators group and never take them out is
    # not a list anybody can rely on. Off unless configured — see
    # services/sso_roles.
    if sso_roles.apply(db, user, userinfo, cfg):
        db.commit()
        db.refresh(user)

    # A code in the address bar, never the token itself.
    #
    # This redirect is a page load: the browser asks nginx for it, and nginx
    # logs `"$request"` — so every sign-in wrote a live bearer token, good for
    # a day, into the frontend container's access log, and into the browser's
    # history, and into the Referer of whatever the page loaded next. The code
    # that goes there instead is worth one exchange, within a minute, and is
    # gone the moment it is spent.
    code = _stash_sso_token(create_access_token(data={"sub": user.email}))
    if code is None:
        logger.error("SSO succeeded but the exchange store is unreachable")
        return RedirectResponse(url=f"{cfg.APP_URL}/login?error=sso_failed")
    return RedirectResponse(url=f"{cfg.APP_URL}/sso-callback?code={code}")