const LOOPBACK_HOSTS = new Set(["127.0.0.1", "localhost", "::1", "[::1]"]);

/** Default web/API origins allowed on loopback binds for the Heute iframe shell. */
const DEFAULT_LOOPBACK_WEB_ORIGINS = [
  "http://127.0.0.1:5173",
  "http://localhost:5173",
  "http://127.0.0.1:3100",
  "http://localhost:3100",
];

export function isLoopbackHost(host) {
  return LOOPBACK_HOSTS.has(host.trim());
}

export function timingSafeStringEqual(supplied, expected) {
  const actual = Buffer.from(expected);
  const candidate = Buffer.from(supplied ?? "");
  if (actual.length !== candidate.length) return false;
  let difference = 0;
  for (let index = 0; index < actual.length; index += 1) {
    difference |= actual[index] ^ candidate[index];
  }
  return difference === 0;
}

export function hasValidBearerToken(authorization, expectedToken) {
  const supplied = authorization?.startsWith("Bearer ") ? authorization.slice(7) : "";
  return timingSafeStringEqual(supplied, expectedToken);
}

export function isPublicCockpitRoute(pathname) {
  return pathname === "/health" || pathname === "/api/health";
}

/** Privileged API routes must never receive Access-Control-Allow-Origin: *. */
export function isPrivilegedCockpitRoute(pathname) {
  if (isPublicCockpitRoute(pathname)) return false;
  return pathname.startsWith("/api/");
}

export function parseCorsOriginAllowlist(value) {
  if (!value?.trim()) return [];
  return [...new Set(value.split(",").map((entry) => entry.trim()).filter(Boolean))];
}

/**
 * Cockpit bind/auth settings. Defaults to loopback-only with no token so local
 * Mission Control keeps working out of the box.
 */
export function resolveCockpitConfig(env) {
  const port = Number.parseInt(env.PORT?.trim() || "3088", 10);
  if (!Number.isInteger(port) || port <= 0 || port > 65_535) {
    throw new Error("PORT is not a valid port number.");
  }

  const host = env.EVOO_COCKPIT_HOST?.trim() || "127.0.0.1";
  const loopback = isLoopbackHost(host);
  const token = env.EVOO_COCKPIT_TOKEN?.trim() || "";

  if (!loopback && token === "") {
    throw new Error(
      "Set EVOO_COCKPIT_TOKEN when EVOO_COCKPIT_HOST is not loopback (127.0.0.1, localhost, or ::1).",
    );
  }

  return {
    port,
    host,
    token: loopback ? null : token,
    requiresAuth: !loopback,
  };
}

/**
 * CORS allowlist. Loopback binds default to local web/API origins; non-loopback
 * binds require an explicit EVOO_COCKPIT_CORS_ORIGIN comma-separated list.
 */
export function resolveCockpitCorsConfig(env, cockpitConfig) {
  const explicit = parseCorsOriginAllowlist(env.EVOO_COCKPIT_CORS_ORIGIN);
  const loopbackBind = isLoopbackHost(cockpitConfig.host);

  if (!loopbackBind && explicit.length === 0) {
    return {
      loopbackBind: false,
      allowedOrigins: [],
      usesDefaultLoopbackOrigins: false,
    };
  }

  const usesDefaultLoopbackOrigins = loopbackBind && explicit.length === 0;
  const allowedOrigins = usesDefaultLoopbackOrigins ? DEFAULT_LOOPBACK_WEB_ORIGINS : explicit;

  return {
    loopbackBind,
    allowedOrigins,
    usesDefaultLoopbackOrigins,
  };
}

/**
 * Resolve the Access-Control-Allow-Origin value for a request.
 * Returns a reflected origin string, null when CORS headers should be omitted,
 * or false when the Origin is present but not allowed.
 */
export function resolveAllowedCorsOrigin(requestOrigin, corsConfig, pathname) {
  const origin = requestOrigin?.trim() ?? "";
  if (!origin) return null;

  if (isPrivilegedCockpitRoute(pathname)) {
    return corsConfig.allowedOrigins.includes(origin) ? origin : false;
  }

  if (corsConfig.loopbackBind && corsConfig.usesDefaultLoopbackOrigins) {
    return corsConfig.allowedOrigins.includes(origin) ? origin : false;
  }

  return corsConfig.allowedOrigins.includes(origin) ? origin : false;
}

export function applyCockpitCorsHeaders(req, res, pathname, corsConfig) {
  res.setHeader("Access-Control-Allow-Methods", "GET, POST, OPTIONS");
  res.setHeader("Access-Control-Allow-Headers", "Content-Type, Authorization");

  const allowed = resolveAllowedCorsOrigin(req.headers.origin, corsConfig, pathname);
  if (typeof allowed === "string") {
    res.setHeader("Access-Control-Allow-Origin", allowed);
    res.setHeader("Vary", "Origin");
  }
  return allowed;
}

export function formatCockpitListenUrl(host, port) {
  const displayHost = host.includes(":") && !host.startsWith("[") ? `[${host}]` : host;
  return `http://${displayHost}:${port}`;
}