import type { Task } from './runner.ts';

type TaskOf<M> = M extends { (...args: any[]): infer R }
  ? R extends Task<infer T, infer A>
    ? Task<T, A>
    : never
  : never;

/**
 * Narrows a task to the descriptor type produced by a specific moroutine.
 *
 * ```ts
 * if (isTask(isPrime, task)) {
 *   // task: Task<boolean, [n: number]>
 * }
 * ```
 *
 * @param moroutine - A function returned by {@link mo}.
 * @param task - A task to test.
 * @returns `true` if `task` was created by `moroutine`.
 */
export function isTask<M extends { readonly id: string; (...args: any[]): Task<any, any> }>(
  moroutine: M,
  task: Task,
): task is TaskOf<M> {
  return task.id === moroutine.id;
}