signature-args.ts

import type { EmptyObject, GetOrElse } from './base';

export type ArgsFor<S> =
  // Signature['Args']
  S extends { Named?: object; Positional?: unknown[] }
    ? {
        Named: GetOrElse<S, 'Named', EmptyObject>;
        Positional: GetOrElse<S, 'Positional', []>;
      }
    : S extends { named?: object; positional?: unknown[] }
    ? {
        Named: GetOrElse<S, 'named', EmptyObject>;
        Positional: GetOrElse<S, 'positional', []>;
      }
    : { Named: EmptyObject; Positional: [] };

/**
 * Converts a variety of types to the expanded arguments type
 * that aligns with the 'Args' portion of the 'Signature' types
 * from ember's helpers, modifiers, components, etc
 */
export type ExpandArgs<T> = T extends any[]
  ? ArgsFor<{ Positional: T }>
  : T extends any
  ? ArgsFor<T>
  : never;

export type Positional<T> = ExpandArgs<T>['Positional'];
export type Named<T> = ExpandArgs<T>['Named'];