/**
 * Next.js auth seam for the complete /api/0pt capability surface.
 *
 * Customer calls use verified Zitadel bearer identity and receive immutable
 * x-0pt-verified-* headers. Explicit machine routes may instead use the
 * shared X-Internal-Token convention; mutation handlers verify it again for
 * defence in depth. The canonical-fact write is one such explicit machine route.
 */
import { NextResponse, type NextRequest } from 'next/server';
import { assertAuthConfigSafe, resolveAuthContext } from '@/src/auth/context';
import { SESSION_COOKIE, verifySession } from '@/lib/auth';
import { verifyInternalServiceToken } from '@/src/auth/internal-token';
import {
  SERVICE_TENANT_SCOPE_HEADER,
  resolveInternalServiceTenants,
} from '@/src/auth/internal-service-tenant';

assertAuthConfigSafe();

export const config = {
  matcher: ['/api/0pt', '/api/0pt/:path*'],
};

const EXEMPT_PATTERNS: RegExp[] = [
  /^\/api\/health(\/|$)/,
  /^\/api\/ready(\/|$)/,
  /^\/api\/admin\/metrics(\/|$)/,
];

/** Routes that may be reached with a service token instead of end-user bearer auth. */
const INTERNAL_SERVICE_ROUTES: RegExp[] = [
  /^\/api\/0pt\/quality\/bridge-run$/,
  // Acquisition engine -> 0pt canonical observation write (machine-to-machine,
  // same X-Internal-Token class as the quality bridge; not a blanket bypass).
  /^\/api\/0pt\/canonical\/facts$/,
  /^\/api\/0pt\/internal\/evidence-outbox\/dispatch$/,
  /^\/api\/0pt\/internal\/er\/candidates$/,
  /^\/api\/0pt\/search\/definitions$/,
];

let _authDiagCount = 0;
let internalScopeWarned = false;

/**
 * Headers that only middleware may set. Anything a client sends under these
 * names is a forgery attempt and is removed before forwarding — including on
 * the internal-token path, which previously passed the original header map
 * through unchanged.
 */
const VERIFIED_HEADERS = [
  'x-0pt-verified-tenant',
  'x-0pt-verified-sub',
  SERVICE_TENANT_SCOPE_HEADER,
] as const;

function stripVerifiedHeaders(req: NextRequest): Headers {
  const forwarded = new Headers(req.headers);
  for (const name of VERIFIED_HEADERS) forwarded.delete(name);
  return forwarded;
}

export async function middleware(req: NextRequest): Promise<NextResponse> {
  const path = req.nextUrl.pathname;
  if (EXEMPT_PATTERNS.some((re) => re.test(path))) return NextResponse.next();

  if (INTERNAL_SERVICE_ROUTES.some((re) => re.test(path)) && verifyInternalServiceToken(req.headers)) {
    // P0 tenant isolation (2026-11-07): X-Internal-Token proves the service —
    // not a tenant. Tenant authority is SERVER CONFIG (INTERNAL_SERVICE_TENANTS),
    // never a client header: an inbound `X-0pt-Internal-Tenant` is ignored and
    // stripped. With no configured tenants the principal has no tenant
    // authority and tenant-scoped writes fail closed with 403.
    const forwarded = stripVerifiedHeaders(req);
    const tenants = resolveInternalServiceTenants();
    if (tenants.length > 1) {
      // The shared X-Internal-Token identifies ONE service process, not a set
      // of independently authenticated principals. A multi-tenant allowlist
      // would let any holder of that shared token choose between all listed
      // tenants, which is exactly the client-controlled authority this guard
      // exists to remove. Multi-tenant service access requires a verified
      // workload-identity binding (CL0UD delegation contract); until that
      // exists, an ambiguous configuration fails closed.
      console.error(
        '[0pt-auth] INTERNAL_SERVICE_TENANTS lists more than one tenant: refusing the internal request until workload-identity binding exists',
      );
      return NextResponse.json(
        {
          error: 'OPT_UNAUTHENTICATED',
          message:
            'internal service tenant scope is ambiguous: configure exactly one tenant until a verified workload-identity binding exists',
        },
        { status: 401 },
      );
    }
    forwarded.set(SERVICE_TENANT_SCOPE_HEADER, tenants.join(','));
    if (tenants.length === 1) {
      forwarded.set('x-0pt-verified-tenant', tenants[0]);
    } else if (tenants.length === 0 && !internalScopeWarned) {
      internalScopeWarned = true;
      console.warn(
        '[0pt-auth] INTERNAL_SERVICE_TENANTS is unset: the internal service principal has no tenant authority; tenant-scoped writes will be denied',
      );
    }
    return NextResponse.next({ request: { headers: forwarded } });
  }

  if (_authDiagCount < 5) {
    _authDiagCount += 1;
    const hasAuth = !!req.headers.get('authorization');
    console.log(
      `[0pt-auth] middleware path=${path} auth_header=${hasAuth} ` +
        `auth_enforce=${process.env.AUTH_ENFORCE ?? 'unset'} ` +
        `node_env=${process.env.NODE_ENV ?? 'unset'} request#${_authDiagCount}`,
    );
  }

  // Browser sessions (Zitadel OIDC -> signed cookie) are a first-class
  // principal for the portal. A Bearer token always wins when present.
  if (!req.headers.get('authorization')) {
    const session = await verifySession(req.cookies.get(SESSION_COOKIE)?.value);
    if (
      session &&
      typeof session.sub === 'string' &&
      typeof session.tenantId === 'string' &&
      typeof session.exp === 'number' &&
      session.exp > Date.now()
    ) {
      const forwarded = stripVerifiedHeaders(req);
      forwarded.set('x-0pt-verified-sub', session.sub);
      forwarded.set('x-0pt-verified-tenant', session.tenantId);
      return NextResponse.next({ request: { headers: forwarded } });
    }
  }

  const decision = await resolveAuthContext(req.headers);
  if (!decision.ok) {
    return NextResponse.json(
      {
        error: decision.code,
        message: decision.message,
        ...(decision.details ? { details: decision.details } : {}),
      },
      { status: decision.status },
    );
  }

  const principal = decision.ctx.principal;
  if (principal) {
    const forwarded = stripVerifiedHeaders(req);
    forwarded.set('x-0pt-verified-sub', principal.sub);
    forwarded.set('x-0pt-verified-tenant', principal.tenantId);
    return NextResponse.next({ request: { headers: forwarded } });
  }

  // No verified principal (explicit AUTH_ENFORCE=false development mode).
  // Never forward a client-named verified header, even in dev.
  return NextResponse.next({ request: { headers: stripVerifiedHeaders(req) } });
}