"""Auth-gate middleware for the dashboard.

Engaged when ``app.state.auth_required is True``. The gate's job:

  1. Allow a small set of routes through unauthenticated (login page,
     ``/auth/*`` OAuth round trip, ``/api/auth/providers``, static
     assets).
  2. For everything else, demand a valid session cookie and attach the
     verified :class:`Session` to ``request.state.session``.
  3. On HTML routes, redirect missing/invalid cookies to ``/login``.
     On ``/api/*`` routes, return 401 JSON.

The middleware is a no-op when ``auth_required`` is False (loopback
mode); the legacy ``_SESSION_TOKEN`` ``auth_middleware`` handles those
binds.
"""
from __future__ import annotations

import logging
from typing import Awaitable, Callable

from fastapi import Request
from fastapi.responses import JSONResponse, RedirectResponse, Response

from hermes_cli.dashboard_auth import list_providers
from hermes_cli.dashboard_auth.audit import AuditEvent, audit_log
from hermes_cli.dashboard_auth.base import ProviderError, RefreshExpiredError
from hermes_cli.dashboard_auth.cookies import read_session_cookies
from hermes_cli.dashboard_auth.public_paths import PUBLIC_API_PATHS

_log = logging.getLogger(__name__)

# Prefixes that bypass the auth gate. Match via ``path == prefix`` or
# ``path.startswith(prefix)`` — so ``/assets/`` (with trailing slash)
# matches ``/assets/foo.css`` but not ``/assetsleak``. Auth-bootstrap
# (login page, OAuth round trip, provider listing) and static asset
# mounts go here.
_GATE_PUBLIC_PREFIXES: tuple[str, ...] = (
    "/auth/login",
    "/auth/callback",
    "/auth/password-login",
    "/auth/logout",
    "/login",
    "/api/auth/providers",
    "/assets/",
    "/favicon.ico",
    "/ds-assets/",
    "/fonts/",
    "/fonts-terminal/",
)


def _path_is_public(path: str) -> bool:
    """True if ``path`` bypasses the OAuth auth gate.

    Two sources of public-ness:

    * :data:`PUBLIC_API_PATHS` — the shared ``/api/*`` allowlist that
      the legacy ``_SESSION_TOKEN`` middleware also honours. Matched
      exactly (no prefix expansion) so adding ``/api/status`` doesn't
      accidentally expose ``/api/status/secret-extension``.
    * :data:`_GATE_PUBLIC_PREFIXES` — auth-bootstrap routes and static
      mounts. Prefix-matched so ``/assets/foo.css`` lights up via
      ``/assets/``.
    """
    if path in PUBLIC_API_PATHS:
        return True
    return any(
        path == prefix or path.startswith(prefix)
        for prefix in _GATE_PUBLIC_PREFIXES
    )


def _client_ip(request: Request) -> str:
    fwd = request.headers.get("x-forwarded-for", "")
    if fwd:
        return fwd.split(",")[0].strip()
    return request.client.host if request.client else ""


def _unauth_response(request: Request, *, reason: str) -> Response:
    """API routes → 401 JSON with ``login_url``; HTML routes → 302 → /login.

    The JSON envelope carries a ``login_url`` field with a ``next=`` query
    string so the SPA's global 401 handler can drop the user back where
    they were after re-auth. The contract is intentionally simple so any
    fetch-wrapper can implement the redirect without parsing details:

        if response.status === 401 && body.error in ("unauthenticated",
                                                       "session_expired"):
            window.location.assign(body.login_url);

    HTML redirects also carry the ``next=`` query string so direct
    navigation to ``/sessions`` (etc.) without a cookie comes back to
    ``/sessions`` after login.

    Under a reverse proxy with ``X-Forwarded-Prefix: /hermes``, the
    ``login_url`` is prefixed (``/hermes/login?next=...``) so the
    browser's window.location.assign / Location: follow lands on the
    proxied login page rather than the bare ``/login`` (which the
    proxy doesn't route to the dashboard).
    """
    from hermes_cli.dashboard_auth.prefix import prefix_from_request

    path = request.url.path
    next_param = _safe_next_target(request)
    prefix = prefix_from_request(request)
    login_url = (
        f"{prefix}/login?next={next_param}" if next_param
        else f"{prefix}/login"
    )

    if path.startswith("/api/"):
        # API routes never get redirects: the browser fetch() API would
        # follow a 302 into the cross-origin OAuth dance opaquely. Return
        # 401 with a structured envelope so the SPA can full-page-navigate
        # to login_url.
        error_code = (
            "session_expired"
            if reason == "invalid_or_expired_session"
            else "unauthenticated"
        )
        return JSONResponse(
            {
                "error": error_code,
                "detail": "Unauthorized",
                "reason": reason,
                "login_url": login_url,
            },
            status_code=401,
        )
    return RedirectResponse(url=login_url, status_code=302)


def _safe_next_target(request: Request) -> str:
    """Build the URL-encoded ``next`` query value, or empty string.

    Only same-origin relative paths are accepted; absolute URLs or
    ``//evil.com`` open-redirect attempts are silently dropped. The empty
    string return means the caller produces a bare ``/login`` URL — fine,
    user lands at the dashboard root after re-auth.
    """
    path = request.url.path
    # Reject anything that doesn't start with "/" or starts with "//"
    # (protocol-relative URL — would open-redirect to an attacker host).
    if not path or not path.startswith("/") or path.startswith("//"):
        return ""
    # Don't redirect back to the auth routes themselves — that loops.
    if any(
        path == p or path.startswith(p)
        for p in ("/login", "/auth/", "/api/auth/")
    ):
        return ""
    # Reject ALL ``/api/*`` paths. The 401-envelope code path fires for
    # any unauthenticated SPA fetch (e.g. ``GET /api/analytics/models``
    # from ModelsPage), and the SPA's global 401 handler full-page
    # navigates to ``login_url``. After the OAuth round trip the user
    # would land on the API URL and see raw JSON instead of the
    # dashboard. SPA routes survive (they don't start with ``/api/``);
    # the SPA's own ``sessionStorage["hermes.lastLocation"]`` fallback
    # in ``web/src/lib/api.ts`` covers the deep-link case.
    if path == "/api" or path.startswith("/api/"):
        return ""
    # Preserve query string if present (e.g. /sessions?page=2).
    query = request.url.query
    target = f"{path}?{query}" if query else path
    # urlencode the whole thing as a single value.
    from urllib.parse import quote
    return quote(target, safe="")


async def gated_auth_middleware(
    request: Request,
    call_next: Callable[[Request], Awaitable[Response]],
) -> Response:
    """Engaged only when ``app.state.auth_required is True``.

    No-op pass-through in loopback mode so the legacy auth_middleware can
    handle those binds via ``_SESSION_TOKEN``.
    """
    if not getattr(request.app.state, "auth_required", False):
        return await call_next(request)

    path = request.url.path
    if _path_is_public(path):
        return await call_next(request)

    at, _rt = read_session_cookies(request)
    if not at and not _rt:
        # Neither token present — no session at all. Nothing to verify or
        # refresh; force login.
        return _unauth_response(request, reason="no_cookie")

    # Try every registered provider's verify_session in turn. Providers
    # MUST return None for tokens they don't recognise (not raise). This
    # lets multiple providers stack — the first one that recognises a
    # token wins.
    #
    # When the access-token cookie is absent but a refresh-token cookie is
    # present, skip verification and go straight to the refresh path below.
    # This is the COMMON expiry case, not an edge case: the access-token
    # cookie is set with ``Max-Age = access_token_expires_in`` (~15 min), so
    # the browser EVICTS it the moment the token lapses, while the
    # refresh-token cookie lives for 30 days. From that point the browser
    # sends only ``hermes_session_rt``. If we bailed on ``not at`` here we'd
    # bounce the user to /login on every expiry despite holding a perfectly
    # good refresh token — defeating the whole transparent-refresh feature.
    session = None
    if at:
        # Try every registered provider's verify_session in turn. A provider
        # that doesn't recognise the token returns None and we move on; the
        # first provider that returns a Session wins.
        #
        # A provider may instead raise ProviderError (its IDP/JWKS is
        # unreachable, so it can neither confirm nor deny the token). With
        # multiple providers stacked, that MUST NOT abort the chain — the
        # token may belong to a *different*, reachable provider. (Concretely:
        # a self-hosted-OIDC session hits the `nous` provider first, which
        # tries to reach Nous Portal's JWKS; if that's unreachable it raises,
        # but the `self-hosted` provider can still verify the token.) So we
        # remember the unreachable error and keep going. Only if NO provider
        # verifies the token AND at least one was unreachable do we surface a
        # 503 — distinguishing "transient IDP outage" (don't force re-login)
        # from "token genuinely invalid" (fall through to refresh/relogin).
        unreachable_provider: str | None = None
        for provider in list_providers():
            try:
                session = provider.verify_session(access_token=at)
            except ProviderError as e:
                _log.warning(
                    "dashboard-auth: provider %r unreachable during verify: %s",
                    provider.name, e,
                )
                audit_log(
                    AuditEvent.SESSION_VERIFY_FAILURE,
                    provider=provider.name,
                    reason="provider_unreachable",
                    ip=_client_ip(request),
                )
                if unreachable_provider is None:
                    unreachable_provider = provider.name
                continue
            if session is not None:
                break
        if session is None and unreachable_provider is not None:
            # No provider could verify the token and at least one couldn't be
            # reached — treat as a transient outage rather than forcing a
            # re-login through a (possibly also-unreachable) refresh.
            return JSONResponse(
                {"detail": f"Auth provider {unreachable_provider!r} unreachable"},
                status_code=503,
            )

    if session is None:
        # Access token is expired/invalid. Before forcing re-login, try to
        # rotate it using the refresh token (if the session cookie carries
        # one). On success we re-set the rotated cookies on the response and
        # serve the request transparently; on RefreshExpiredError (RT dead /
        # revoked / reuse-detected) we fall through to clear-and-relogin.
        refreshed = _attempt_refresh(request, refresh_token=_rt)
        if refreshed is not None:
            new_session, refreshing_provider = refreshed
            request.state.session = new_session
            response = await call_next(request)
            # Persist the ROTATED tokens. Portal rotates the refresh token on
            # every refresh and runs reuse-detection, so writing the new RT
            # back is mandatory: a stale RT cookie would replay a rotated
            # token on the next refresh and (outside Portal's grace) revoke
            # the whole session. Bind cookie Secure/Path to the request shape.
            from hermes_cli.dashboard_auth.cookies import (
                detect_https,
                set_session_cookies,
            )
            from hermes_cli.dashboard_auth.prefix import prefix_from_request

            set_session_cookies(
                response,
                access_token=new_session.access_token,
                refresh_token=new_session.refresh_token,
                access_token_expires_in=_expires_in_seconds(new_session),
                use_https=detect_https(request),
                prefix=prefix_from_request(request),
            )
            audit_log(
                AuditEvent.REFRESH_SUCCESS,
                provider=refreshing_provider,
                user_id=new_session.user_id,
                ip=_client_ip(request),
            )
            return response

        audit_log(
            AuditEvent.SESSION_VERIFY_FAILURE,
            reason="no_provider_recognises",
            ip=_client_ip(request),
        )
        response = _unauth_response(request, reason="invalid_or_expired_session")
        # Clear the dead cookies so the browser doesn't keep sending them.
        # Refresh already failed (or there was no RT), so the only correct
        # next step is full re-auth via /login. Importing locally avoids a
        # cycle with cookies → middleware at module load. Pass the active
        # prefix so the deletion's Path matches the set-Path (otherwise
        # the browser ignores it).
        from hermes_cli.dashboard_auth.cookies import clear_session_cookies
        from hermes_cli.dashboard_auth.prefix import prefix_from_request
        clear_session_cookies(response, prefix=prefix_from_request(request))
        return response

    request.state.session = session
    return await call_next(request)


def _expires_in_seconds(session) -> int:
    """Seconds until the access token's ``exp``, floored at 60.

    Mirrors the auth-route's ``max(60, exp - now)`` so the access-token
    cookie's Max-Age tracks the token lifetime even on a slightly skewed
    clock. ``time`` imported locally to keep the module's import surface
    minimal.
    """
    import time

    return max(60, int(session.expires_at) - int(time.time()))


def _attempt_refresh(request: Request, *, refresh_token):
    """Try to rotate an expired session via the refresh token.

    Returns ``(new_session, provider_name)`` on success, or ``None`` if
    there's no RT or every provider's ``refresh_session`` failed with
    ``RefreshExpiredError`` (dead/revoked/reuse-detected RT → force re-login).

    A ``ProviderError`` (Portal unreachable) is NOT swallowed into a re-login
    here — re-raising would 500 the request; instead we log and return None so
    the caller forces a clean re-login, which is the safer UX than a hard
    error on a transient network blip during the narrow refresh window.
    """
    if not refresh_token:
        return None
    for provider in list_providers():
        try:
            new_session = provider.refresh_session(refresh_token=refresh_token)
        except RefreshExpiredError:
            # This provider owns the RT but it's dead — stop trying others
            # (an RT belongs to exactly one provider) and force re-login.
            audit_log(
                AuditEvent.REFRESH_FAILURE,
                provider=provider.name,
                reason="refresh_expired",
                ip=_client_ip(request),
            )
            return None
        except ProviderError as e:
            _log.warning(
                "dashboard-auth: provider %r unreachable during refresh: %s",
                provider.name, e,
            )
            audit_log(
                AuditEvent.REFRESH_FAILURE,
                provider=provider.name,
                reason="provider_unreachable",
                ip=_client_ip(request),
            )
            return None
        if new_session is not None:
            return new_session, provider.name
    return None