import { limitAsync } from "../promise/limitAsync.mjs";
import { flatten } from "./flatten.mjs";
//#region src/array/flatMapAsync.ts
/**
* Maps each element in an array using an async callback function and flattens the result by one level.
*
* This is equivalent to calling `mapAsync` followed by `flat(1)`, but more efficient.
* Each callback should return an array, and all returned arrays are concatenated into
* a single output array.
*
* @template T - The type of elements in the input array.
* @template R - The type of elements in the arrays returned by the callback.
* @param array The array to transform.
* @param callback An async function that transforms each element into an array.
* @param [options] Optional configuration object.
* @param [options.concurrency] Maximum number of concurrent async operations. If not specified, all operations run concurrently.
* @returns A promise that resolves to a flattened array of transformed values.
* @example
* const users = [{ id: 1 }, { id: 2 }];
* const allPosts = await flatMapAsync(users, async (user) => {
*   return await fetchUserPosts(user.id);
* });
* // Returns: [post1, post2, post3, ...] (all posts from all users)
*
* @example
* // With concurrency limit
* const numbers = [1, 2, 3];
* const results = await flatMapAsync(
*   numbers,
*   async (n) => await fetchRelatedItems(n),
*   { concurrency: 2 }
* );
* // Processes at most 2 operations concurrently
*/
async function flatMapAsync(array, callback, options) {
	if (options?.concurrency != null) callback = limitAsync(callback, options.concurrency);
	return flatten(await Promise.all(array.map(callback)));
}
//#endregion
export { flatMapAsync };
