"""
Google OAuth 2.0 sign-in.

Flow:
  1. GET /auth/google          → redirect to Google's consent page
  2. GET /auth/google/callback → exchange code, look up user, set JWT cookie

Users must be pre-registered by Scott before they can sign in:
  cd cortex && .venv/bin/python manage_passwords.py google-add <username> <email>

Routes are public (added to _PUBLIC_PREFIXES in auth_middleware.py).
"""

import json
import logging
import secrets
import urllib.parse
import urllib.request

from fastapi import APIRouter, Request
from fastapi.responses import HTMLResponse, RedirectResponse, Response

from auth_utils import COOKIE_NAME, create_token, find_user_by_google, link_google
from config import settings
from persona import list_user_personas

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

_GOOGLE_AUTH_URL  = "https://accounts.google.com/o/oauth2/v2/auth"
_GOOGLE_TOKEN_URL = "https://oauth2.googleapis.com/token"
_GOOGLE_USERINFO  = "https://openidconnect.googleapis.com/v1/userinfo"
_STATE_COOKIE     = "oauth_state"
_STATE_MAX_AGE    = 600  # 10 minutes — plenty of time to complete the flow


@router.get("/auth/google", include_in_schema=False)
async def google_login():
    if not settings.google_client_id:
        return HTMLResponse("Google sign-in is not configured on this server.", status_code=503)

    state = secrets.token_urlsafe(16)
    params = urllib.parse.urlencode({
        "client_id":     settings.google_client_id,
        "redirect_uri":  f"{settings.cortex_base_url}/auth/google/callback",
        "response_type": "code",
        "scope":         "openid email profile",
        "state":         state,
        "access_type":   "online",
        "prompt":        "select_account",
    })

    resp = RedirectResponse(f"{_GOOGLE_AUTH_URL}?{params}", status_code=302)
    resp.set_cookie(_STATE_COOKIE, state, max_age=_STATE_MAX_AGE, httponly=True, samesite="lax")
    return resp


@router.get("/auth/google/callback", include_in_schema=False)
async def google_callback(
    request: Request,
    code: str = "",
    state: str = "",
    error: str = "",
):
    if error:
        return _error_page(f"Google sign-in was cancelled or denied: {error}")

    if not code:
        return _error_page("No authorisation code returned by Google.")

    # CSRF check — state must match what we stored in the cookie
    stored_state = request.cookies.get(_STATE_COOKIE)
    if not stored_state or stored_state != state:
        return _error_page("State mismatch — please try signing in again.")

    # Exchange authorisation code for tokens
    try:
        token_data = _exchange_code(code)
    except Exception as e:
        logger.error("Google token exchange failed: %s", e)
        return _error_page("Could not complete sign-in with Google. Please try again.")

    access_token = token_data.get("access_token")
    if not access_token:
        return _error_page("No access token returned by Google.")

    # Fetch the user's profile
    try:
        userinfo = _get_userinfo(access_token)
    except Exception as e:
        logger.error("Google userinfo fetch failed: %s", e)
        return _error_page("Could not retrieve your Google profile. Please try again.")

    google_sub   = userinfo.get("sub", "")
    google_email = userinfo.get("email", "")

    if not google_sub or not google_email:
        return _error_page("Your Google account didn't return a usable email address.")

    # Match to a Cortex user
    username = find_user_by_google(google_sub, google_email)
    if not username:
        logger.warning("Google sign-in rejected: no account for %s (%s)", google_sub, google_email)
        return _error_page(
            f"Your Google account (<strong>{google_email}</strong>) isn't registered with Cortex.<br><br>"
            "Contact Scott to get access."
        )

    # Persist the stable sub so future lookups use it (not just email)
    link_google(username, google_sub, google_email)

    personas = list_user_personas(username)
    if not personas:
        return _error_page("No personas are configured for your account yet. Contact Scott.")

    logger.info("Google sign-in: %s (%s)", username, google_email)
    resp = RedirectResponse(f"/{username}/{personas[0]}", status_code=302)
    _set_session_cookie(resp, username)
    resp.delete_cookie(_STATE_COOKIE)
    return resp


# ---------------------------------------------------------------------------
# Private helpers
# ---------------------------------------------------------------------------

def _exchange_code(code: str) -> dict:
    body = urllib.parse.urlencode({
        "code":          code,
        "client_id":     settings.google_client_id,
        "client_secret": settings.google_client_secret,
        "redirect_uri":  f"{settings.cortex_base_url}/auth/google/callback",
        "grant_type":    "authorization_code",
    }).encode()
    req = urllib.request.Request(
        _GOOGLE_TOKEN_URL,
        data=body,
        headers={"Content-Type": "application/x-www-form-urlencoded"},
        method="POST",
    )
    with urllib.request.urlopen(req, timeout=10) as resp:
        return json.loads(resp.read())


def _get_userinfo(access_token: str) -> dict:
    req = urllib.request.Request(
        _GOOGLE_USERINFO,
        headers={"Authorization": f"Bearer {access_token}"},
    )
    with urllib.request.urlopen(req, timeout=10) as resp:
        return json.loads(resp.read())


def _set_session_cookie(response: Response, username: str) -> None:
    token = create_token(username)
    response.set_cookie(
        COOKIE_NAME,
        token,
        max_age=settings.jwt_expire_days * 86400,
        httponly=True,
        samesite="lax",
        secure=False,  # set True if terminating TLS at the app layer (not behind a proxy)
    )


def _error_page(message: str) -> HTMLResponse:
    html = f"""<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Cortex — Sign In Failed</title>
  <link rel="preconnect" href="https://fonts.googleapis.com">
  <link href="https://fonts.googleapis.com/css2?family=Inter:wght@100..900&display=swap" rel="stylesheet">
  <style>
    *, *::before, *::after {{ box-sizing: border-box; margin: 0; padding: 0; }}
    body {{
      min-height: 100vh; display: flex; align-items: center; justify-content: center;
      background: #0f1117; font-family: 'Inter', system-ui; font-weight: 450;
      -webkit-font-smoothing: antialiased; color: #e2e8f0;
    }}
    .card {{
      background: #1a1d27; border: 1px solid #2d3148; border-radius: 12px;
      padding: 2.5rem 2rem; width: 100%; max-width: 420px; text-align: center;
    }}
    h1 {{ font-size: 1.25rem; font-weight: 700; color: #f87171; margin-bottom: 1rem; }}
    p {{ font-size: 0.9rem; color: #94a3b8; margin-bottom: 1.75rem; line-height: 1.65; }}
    a {{
      display: inline-block; padding: 0.6rem 1.5rem;
      background: #7c3aed; border-radius: 6px; color: #fff;
      text-decoration: none; font-size: 0.9rem; font-weight: 600;
      transition: background 0.15s;
    }}
    a:hover {{ background: #6d28d9; }}
  </style>
</head>
<body>
  <div class="card">
    <h1>Sign In Failed</h1>
    <p>{message}</p>
    <a href="/login">← Back to Sign In</a>
  </div>
</body>
</html>"""
    return HTMLResponse(html, status_code=403)