// Attribute getter
export function attr<K extends string>(
  name: K,
): <O extends Record<K, O[K]>>(obj: O) => O[K] {
  return (obj) => obj[name];
}

type DefinedKeys<T> =
  ({ [P in keyof T]: T[P] extends undefined ? never : P })[keyof T];
type Defined<T> = Pick<T, DefinedKeys<T>>;

// Removes undefined values from objects
export function defined<T>(obj: T): Defined<T> {
  return Object.fromEntries(
    Object.entries(obj).filter(([_, value]) => typeof value !== "undefined"),
  ) as any;
}

// Apply options to a default object
export function options<T extends { [name: string]: any }>(
  defaults: T,
  ...options: Partial<T>[]
) {
  for (let opts of options) {
    defaults = { ...defaults, ...defined(opts) };
  }
  return defaults;
}