from datetime import timedelta
from typing import Annotated

from fastapi import Depends, HTTPException, Request, Response, status
from sqlalchemy import select
from sqlalchemy.orm import Session

from app.config import settings
from app.db import get_db
from app.models import Setting, User, UserSession
from app.security import (
    hash_token,
    new_token,
    tokens_equal,
    utcnow,
)

SESSION_COOKIE = "ea_session"
CSRF_COOKIE = "ea_csrf"
CSRF_HEADER = "X-CSRF-Token"

DbSession = Annotated[Session, Depends(get_db)]


# --------------------------------------------------------------------------
# Laufzeit-Einstellungen
# --------------------------------------------------------------------------

def get_setting(db: Session, key: str, default: str = "") -> str:
    row = db.get(Setting, key)
    return row.value if row else default


def set_setting(db: Session, key: str, value: str) -> None:
    row = db.get(Setting, key)
    if row is None:
        db.add(Setting(key=key, value=value))
    else:
        row.value = value


def registration_locked_by_env() -> bool:
    """True, wenn ALLOW_SELF_REGISTRATION hart auf true/false steht.
    Dann darf die Admin-Oberflaeche den Wert nicht aendern."""
    return settings.allow_self_registration in ("true", "false")


def self_registration_enabled(db: Session) -> bool:
    mode = settings.allow_self_registration
    if mode == "true":
        return True
    if mode == "false":
        return False
    # mode == "admin": die Laufzeiteinstellung entscheidet.
    return get_setting(db, "allow_self_registration", "true") == "true"


# --------------------------------------------------------------------------
# Sessions
# --------------------------------------------------------------------------

def create_session(db: Session, user: User, response: Response) -> UserSession:
    # Spät importiert: runtime_settings greift auf get_setting in dieser
    # Datei zu, ein Import auf Modulebene wäre ein Kreis.
    from app.runtime_settings import get_duration

    days = get_duration(db, "session_days")

    raw = new_token()
    csrf = new_token()
    sess = UserSession(
        token_hash=hash_token(raw),
        user_id=user.id,
        csrf_token=csrf,
        expires_at=utcnow() + timedelta(days=days),
    )
    db.add(sess)
    db.flush()

    max_age = days * 24 * 3600
    # HttpOnly: fuer JavaScript unsichtbar, damit ein XSS-Fund das Token
    # nicht abgreifen kann.
    response.set_cookie(
        SESSION_COOKIE, raw, max_age=max_age, httponly=True,
        secure=settings.cookie_secure, samesite="lax", path="/",
    )
    # Bewusst NICHT HttpOnly: der Client muss den Wert lesen und als
    # Header zurueckschicken koennen (Double-Submit-Verfahren).
    response.set_cookie(
        CSRF_COOKIE, csrf, max_age=max_age, httponly=False,
        secure=settings.cookie_secure, samesite="lax", path="/",
    )
    return sess


def destroy_session(db: Session, request: Request, response: Response) -> None:
    raw = request.cookies.get(SESSION_COOKIE)
    if raw:
        sess = db.scalar(
            select(UserSession).where(UserSession.token_hash == hash_token(raw))
        )
        if sess:
            db.delete(sess)
    response.delete_cookie(SESSION_COOKIE, path="/")
    response.delete_cookie(CSRF_COOKIE, path="/")


def _load_session(db: Session, request: Request) -> UserSession | None:
    raw = request.cookies.get(SESSION_COOKIE)
    if not raw:
        return None
    sess = db.scalar(
        select(UserSession).where(UserSession.token_hash == hash_token(raw))
    )
    if sess is None:
        return None
    if sess.expires_at <= utcnow():
        db.delete(sess)
        db.commit()
        return None
    return sess


# --------------------------------------------------------------------------
# Abhaengigkeiten fuer Routen
# --------------------------------------------------------------------------

_UNSAFE = {"POST", "PUT", "PATCH", "DELETE"}


def current_user(request: Request, db: DbSession) -> User:
    sess = _load_session(db, request)
    if sess is None:
        raise HTTPException(status.HTTP_401_UNAUTHORIZED, "Nicht angemeldet")

    if request.method in _UNSAFE:
        supplied = request.headers.get(CSRF_HEADER, "")
        if not supplied or not tokens_equal(supplied, sess.csrf_token):
            raise HTTPException(status.HTTP_403_FORBIDDEN, "CSRF-Token fehlt oder ungültig")

    user = db.get(User, sess.user_id)
    if user is None or not user.is_active:
        raise HTTPException(status.HTTP_401_UNAUTHORIZED, "Konto nicht aktiv")

    # Nur einmal pro Stunde schreiben, sonst erzeugt jeder Request ein
    # UPDATE. Der Zeitstempel am Konto ist die Grundlage der
    # automatischen Deaktivierung - er muss auch dann mitlaufen, wenn
    # sich jemand monatelang nicht neu anmeldet, weil die Sitzung hält.
    if utcnow() - sess.last_seen_at > timedelta(hours=1):
        sess.last_seen_at = utcnow()
        user.last_seen_at = utcnow()
        db.commit()

    return user


CurrentUser = Annotated[User, Depends(current_user)]


def verified_user(user: CurrentUser) -> User:
    if user.verified_at is None:
        raise HTTPException(
            status.HTTP_403_FORBIDDEN, "E-Mail-Adresse noch nicht bestätigt"
        )
    # Alles ausser GET /api/auth/me und POST /api/auth/password/change
    # haengt an dieser Abhaengigkeit - der Zwang wirkt also flaechendeckend,
    # ohne dass jede Route ihn einzeln pruefen muesste.
    if user.must_change_password:
        raise HTTPException(
            status.HTTP_403_FORBIDDEN,
            "Das Startpasswort muss zuerst geändert werden: "
            "POST /api/auth/password/change",
        )
    return user


VerifiedUser = Annotated[User, Depends(verified_user)]


def admin_user(user: VerifiedUser) -> User:
    if not user.is_admin:
        raise HTTPException(status.HTTP_403_FORBIDDEN, "Administratorrechte erforderlich")
    return user


AdminUser = Annotated[User, Depends(admin_user)]


def client_ip(request: Request) -> str:
    """Fuer Rate Limiting. Hinter einem Reverse Proxy liefert
    request.client.host die Proxy-IP - ab Phase 3 setzen wir dafuer
    ProxyHeadersMiddleware mit einer Liste vertrauenswuerdiger Hosts."""
    return request.client.host if request.client else "unknown"