"""
Client-portal auth — the swappable gate (see docs/CLIENT_PORTAL.md).

M1-M3 ride on an interim signed "magic URL": an unguessable token in the link
mints a signed session cookie.  Every portal route depends on get_current_client();
M4 replaces the backing (magic-link / accounts) without touching routes/templates.

The cookie carries the ACCESS-TOKEN id (not the client id) and is re-validated
against the DB on every request, so revoking a link (revoked_at) kills its live
sessions on the next request — not just future clicks.

No new dependency: the cookie is signed with stdlib HMAC-SHA256 over a SECRET_KEY.
"""

import os
import hmac
import json
import time
import base64
import hashlib
import logging
from datetime import datetime

from fastapi import Request, Depends
from sqlalchemy.orm import Session

from backend.database import get_db
from backend.models import Client, ClientAccessToken

logger = logging.getLogger(__name__)

# Signing secret for portal session cookies. MUST be set to a real secret in prod
# (env). The insecure default only exists so dev/test boots without config.
SECRET_KEY = os.getenv("SECRET_KEY", "dev-insecure-change-me")
if SECRET_KEY == "dev-insecure-change-me":
    logger.warning("[PORTAL] SECRET_KEY is the insecure default — set SECRET_KEY in prod.")

COOKIE_NAME = "portal_session"
COOKIE_MAX_AGE = 60 * 60 * 24 * 30  # 30 days


class PortalAuthError(Exception):
    """Raised by get_current_client when there's no valid portal session.
    Handled centrally in main.py: HTML routes get the access-required page,
    /portal/api/* routes get a 401 JSON."""


# -- token + cookie primitives ----------------------------------------------

def hash_token(raw: str) -> str:
    """sha256 hex of a raw access-token secret (what we store + look up by)."""
    return hashlib.sha256(raw.encode()).hexdigest()


def _sign(body: str) -> str:
    return hmac.new(SECRET_KEY.encode(), body.encode(), hashlib.sha256).hexdigest()


def make_session_cookie(token_id: str) -> str:
    body = base64.urlsafe_b64encode(
        json.dumps({"tid": token_id, "iat": int(time.time())}).encode()
    ).decode()
    return f"{body}.{_sign(body)}"


def _read_session_cookie(value: str):
    """Return the token id from a signed cookie, or None if missing/tampered."""
    try:
        body, sig = value.rsplit(".", 1)
    except (ValueError, AttributeError):
        return None
    if not hmac.compare_digest(sig, _sign(body)):
        return None
    try:
        data = json.loads(base64.urlsafe_b64decode(body.encode()))
    except Exception:
        return None
    return data.get("tid")


# -- the dependency every portal route uses ---------------------------------

def get_current_client(request: Request, db: Session = Depends(get_db)) -> Client:
    """Resolve the authenticated client, or raise PortalAuthError.

    Re-validates the access token on every request so a revoked link / disabled
    client drops the session immediately."""
    cookie = request.cookies.get(COOKIE_NAME)
    token_id = _read_session_cookie(cookie) if cookie else None
    if not token_id:
        raise PortalAuthError()
    tok = db.query(ClientAccessToken).filter_by(id=token_id, revoked_at=None).first()
    if not tok:
        raise PortalAuthError()
    client = db.query(Client).filter_by(id=tok.client_id, active=True).first()
    if not client:
        raise PortalAuthError()
    return client


def resolve_token(raw_token: str, db: Session):
    """Validate a raw magic-URL token. Returns (ClientAccessToken, Client) on
    success, or (None, None). Also stamps last_used_at."""
    tok = db.query(ClientAccessToken).filter_by(
        token_hash=hash_token(raw_token), revoked_at=None
    ).first()
    if not tok:
        return None, None
    client = db.query(Client).filter_by(id=tok.client_id, active=True).first()
    if not client:
        return None, None
    tok.last_used_at = datetime.utcnow()
    db.commit()
    return tok, client