function readEnvNumber(key: string, fallback: number): number {
  const raw = import.meta.env[key];
  if (raw === undefined || raw === "") return fallback;
  const parsed = Number(raw);
  return Number.isFinite(parsed) ? parsed : fallback;
}

function readEnvString(key: string, fallback: string): string {
  const raw = import.meta.env[key];
  return raw === undefined || raw === "" ? fallback : raw;
}

// Room-scale defaults (a 4m x 3m living room -- see roomLayout.ts, which
// derives its own wall placement from these same two numbers so the two
// modules can't drift apart). Tiles cleanly into 1m floor/wall segments.
export const FLY_AREA_CONFIG = {
  count: readEnvNumber("VITE_FLY_COUNT", 12),
  widthMm: readEnvNumber("VITE_FLY_AREA_WIDTH_MM", 4000),
  depthMm: readEnvNumber("VITE_FLY_AREA_DEPTH_MM", 3000),
  heightMm: readEnvNumber("VITE_FLY_AREA_HEIGHT_MM", 0),
};

// flyyt-backend (VDA5050 fly-fleet simulator) connectivity. Same-origin
// defaults so "npm run build" served by the backend container (see
// flyyt/backend/src/flyyt_backend/main.py) works with zero config; override
// for local dev when the backend/NATS run on different hosts/ports.
export const BACKEND_CONFIG = {
  apiUrl: readEnvString("VITE_FLYYT_API_URL", ""),
  natsWsUrl: readEnvString("VITE_NATS_WS_URL", "ws://localhost:8080"),
};

/**
 * Builds a same-origin API URL. Deliberately NOT `/${path}` when apiUrl is
 * unset -- this app can be served behind an arbitrary path prefix (e.g.
 * /cell/flyyt/ on a Nova instance), and a root-absolute fetch path ignores
 * that prefix entirely (hits http://host/roster instead of
 * http://host/cell/flyyt/roster). A plain relative path resolves against
 * the page's <base href> instead (injected server-side to match BASE_PATH
 * -- see main.py's index.html serving), which is prefix-correct wherever
 * this is deployed, including plain root-path local dev (no <base>, so it
 * just resolves against "/").
 */
export function apiPath(path: string): string {
  return BACKEND_CONFIG.apiUrl ? `${BACKEND_CONFIG.apiUrl}/${path}` : path;
}