export function flattenSelector(selector) {
  // If selector uses $and format, convert to plain object selector
  if (Array.isArray(selector.$and)) {
    selector.$and.forEach(sel => {
      Object.assign(selector, flattenSelector(sel));
    });

    delete selector.$and
  }

  const obj = {}

  Object.entries(selector).forEach(([key, value]) => {
    // Ignoring logical selectors (https://docs.mongodb.com/manual/reference/operator/query/#logical)
    if (!key.startsWith("$")) {
      if (typeof value === 'object' && value !== null) {
        if (value.$eq !== undefined) {
          obj[key] = value.$eq
        } else if (Array.isArray(value.$in) && value.$in.length === 1) {
          obj[key] = value.$in[0]
        } else if (Object.keys(value).every(v => !(typeof v === "string" && v.startsWith("$")))) {
          obj[key] = value
        }
      } else {
        obj[key] = value
      }
    }
  })
  
  return obj
}