whilst.js

import noop from 'lodash/noop';
import rest from './internal/rest';

import onlyOnce from './internal/onlyOnce';

/**
 * Repeatedly call `iteratee`, while `test` returns `true`. Calls `callback` when
 * stopped, or an error occurs.
 *
 * @name whilst
 * @static
 * @memberOf module:ControlFlow
 * @method
 * @category Control Flow
 * @param {Function} test - synchronous truth test to perform before each
 * execution of `iteratee`. Invoked with ().
 * @param {Function} iteratee - A function which is called each time `test` passes.
 * The function is passed a `callback(err)`, which must be called once it has
 * completed with an optional `err` argument. Invoked with (callback).
 * @param {Function} [callback] - A callback which is called after the test
 * function has failed and repeated execution of `iteratee` has stopped. `callback`
 * will be passed an error and any arguments passed to the final `iteratee`'s
 * callback. Invoked with (err, [results]);
 * @returns undefined
 * @example
 *
 * var count = 0;
 * async.whilst(
 *     function() { return count < 5; },
 *     function(callback) {
 *         count++;
 *         setTimeout(function() {
 *             callback(null, count);
 *         }, 1000);
 *     },
 *     function (err, n) {
 *         // 5 seconds have passed, n = 5
 *     }
 * );
 */
export default function whilst(test, iteratee, callback) {
    callback = onlyOnce(callback || noop);
    if (!test()) return callback(null);
    var next = rest(function(err, args) {
        if (err) return callback(err);
        if (test()) return iteratee(next);
        callback.apply(null, [null].concat(args));
    });
    iteratee(next);
}