/**
 * Functions that does nothing (useful for default callbacks)
 */
export function nop(...args: any[]): any {
}

/**
 * Identity function (returns the sole argument untouched)
 */
export function identity<T>(input: T): T {
  return input;
}

/**
 * Partially apply fixed arguments to a function with named arguments
 */
export function partial<A extends object, PA extends Partial<A>, RA extends any[], R>(fixedargs: PA, func: (args: A, ...rest: RA) => R): (args: Omit<A, keyof PA>, ...rest: RA) => R {
  return (args: Omit<A, keyof PA>, ...rest: RA) => func({ ...fixedargs, ...args } as any, ...rest);
}

export type cmpArgs = Readonly<{ key: (item: any) => any, reverse: boolean }>
export const cmpDefaults: cmpArgs = { key: identity, reverse: false }
/**
 * Compare operator, that can be used in sort() calls.
 */
export function cmp(args?: Partial<cmpArgs>): (a: any, b: any) => number {
  const fargs = { ...cmpDefaults, ...args };
  return (a, b) => {
    const ka = fargs.key(a);
    const kb = fargs.key(b);
    if (ka > kb) {
      return fargs.reverse ? -1 : 1;
    } else if (ka < kb) {
      return fargs.reverse ? 1 : -1;
    } else {
      return 0;
    }
  }
}