/**
 * Next.js auth seam for /api/0pt. Browser/user calls use verified bearer/session.
 * Explicit machine routes accept: (1) legacy X-Internal-Token + server-configured
 * single-tenant scope, or (2) verified CL0UD workload JWT (tenant/capabilities
 * from claims, never client headers). Deny by default.
 */
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_CAPABILITIES_HEADER,
  SERVICE_TENANT_SCOPE_HEADER,
  resolveInternalServiceTenants,
} from '@/src/auth/internal-service-tenant';
import { isCl0udWorkloadConfigured, looksLikeCl0udWorkloadToken, verifyCl0udWorkloadToken } from '@/src/auth/cl0ud-workload';

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

const EXEMPT_PATTERNS: RegExp[] = [/^\/api\/health(\/|$)/, /^\/api\/ready(\/|$)/, /^\/api\/admin\/metrics(\/|$)/];
const INTERNAL_SERVICE_ROUTES: RegExp[] = [
  /^\/api\/0pt\/quality\/bridge-run$/,
  /^\/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,
  SERVICE_CAPABILITIES_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;
}

function bearerToken(req: NextRequest): string | null {
  const h = req.headers.get('authorization');
  if (!h?.toLowerCase().startsWith('bearer ')) return null;
  return h.slice(7).trim() || null;
}

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))) {
    // (1) Legacy shared internal token (engine/n8n). 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.
    if (verifyInternalServiceToken(req.headers)) {
      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 } });
    }

    // (2) CL0UD workload JWT (dual-accept): tenant and capabilities come from
    // verified claims only. Attempted only when the issuer is configured or the
    // presented token is issued by it; an invalid one is a 401, never a
    // fall-through to an unauthenticated dev path.
    const bt = bearerToken(req);
    if (bt && (isCl0udWorkloadConfigured() || looksLikeCl0udWorkloadToken(bt))) {
      try {
        const principal = await verifyCl0udWorkloadToken(bt);
        const forwarded = stripVerifiedHeaders(req);
        forwarded.set('x-0pt-verified-sub', principal.sub);
        forwarded.set('x-0pt-verified-tenant', principal.tenantId);
        forwarded.set(SERVICE_CAPABILITIES_HEADER, principal.capabilities.join(','));
        return NextResponse.next({ request: { headers: forwarded } });
      } catch (err) {
        const message = err instanceof Error ? err.message : 'workload token verification failed';
        return NextResponse.json({ error: 'OPT_UNAUTHENTICATED', message }, { status: 401 });
      }
    }
  }

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

  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) } });
}