import concatLimit from './concatLimit.js'
import awaitify from './internal/awaitify.js'

/**
 * Applies `iteratee` to each item in `coll`, concatenating the results. Returns
 * the concatenated list. The `iteratee`s are called in parallel, and the
 * results are concatenated as they return. The results array will be returned in
 * the original order of `coll` passed to the `iteratee` function.
 *
 * @name concat
 * @static
 * @memberOf module:Collections
 * @method
 * @category Collection
 * @alias flatMap
 * @param {Array|Iterable|AsyncIterable|Object} coll - A collection to iterate over.
 * @param {AsyncFunction} iteratee - A function to apply to each item in `coll`,
 * which should use an array as its result. Invoked with (item, callback).
 * @param {Function} [callback] - A callback which is called after all the
 * `iteratee` functions have finished, or an error occurs. Results is an array
 * containing the concatenated results of the `iteratee` function. Invoked with
 * (err, results).
 * @returns A Promise, if no callback is passed
 * @example
 *
 * // dir1 is a directory that contains file1.txt, file2.txt
 * // dir2 is a directory that contains file3.txt, file4.txt
 * // dir3 is a directory that contains file5.txt
 * // dir4 does not exist
 *
 * let directoryList = ['dir1','dir2','dir3'];
 * let withMissingDirectoryList = ['dir1','dir2','dir3', 'dir4'];
 *
 * // Using callbacks
 * async.concat(directoryList, fs.readdir, function(err, results) {
 *    if (err) {
 *        console.log(err);
 *    } else {
 *        console.log(results);
 *        // [ 'file1.txt', 'file2.txt', 'file3.txt', 'file4.txt', file5.txt ]
 *    }
 * });
 *
 * // Error Handling
 * async.concat(withMissingDirectoryList, fs.readdir, function(err, results) {
 *    if (err) {
 *        console.log(err);
 *        // [ Error: ENOENT: no such file or directory ]
 *        // since dir4 does not exist
 *    } else {
 *        console.log(results);
 *    }
 * });
 *
 * // Using Promises
 * async.concat(directoryList, fs.readdir)
 * .then(results => {
 *     console.log(results);
 *     // [ 'file1.txt', 'file2.txt', 'file3.txt', 'file4.txt', file5.txt ]
 * }).catch(err => {
 *      console.log(err);
 * });
 *
 * // Error Handling
 * async.concat(withMissingDirectoryList, fs.readdir)
 * .then(results => {
 *     console.log(results);
 * }).catch(err => {
 *     console.log(err);
 *     // [ Error: ENOENT: no such file or directory ]
 *     // since dir4 does not exist
 * });
 *
 * // Using async/await
 * async () => {
 *     try {
 *         let results = await async.concat(directoryList, fs.readdir);
 *         console.log(results);
 *         // [ 'file1.txt', 'file2.txt', 'file3.txt', 'file4.txt', file5.txt ]
 *     } catch (err) {
 *         console.log(err);
 *     }
 * }
 *
 * // Error Handling
 * async () => {
 *     try {
 *         let results = await async.concat(withMissingDirectoryList, fs.readdir);
 *         console.log(results);
 *     } catch (err) {
 *         console.log(err);
 *         // [ Error: ENOENT: no such file or directory ]
 *         // since dir4 does not exist
 *     }
 * }
 *
 */
function concat(coll, iteratee, callback) {
    return concatLimit(coll, Infinity, iteratee, callback)
}
export default awaitify(concat, 3);