import {Function} from './Function'
import {Parameters} from './Parameters'
import {Formats} from '../Iteration/_Internal'
import {Length as TLength} from '../Tuple/Length'

/** Extract arguments' length from a **`Function`**
 * @param F to extract from
 * @param fmt output (?=`'n'`)
 * @returns **`string`** or **`number`**
 * @example
 * ```ts
 * import {F} from 'ts-toolbelt'
 *
 * const fn = (a1: any, a2: any) => {}
 *
 * type test0 = F.LengthOf<typeof fn>               // 2
 *
 * type test1 = F.LengthOf<(a1?: any) => any>       // 0 | 1
 *
 * type test2 = F.LengthOf<(...a: any[]) => any>    // number
 * ```
 */
export type Length<Fn extends Function, fmt extends Formats = 'n'> =
    TLength<Parameters<Fn>, fmt>