source: trip-planner-front/node_modules/p-limit/index.js@ e29cc2e

'use strict';
const pTry = require('p-try');

const pLimit = concurrency => {
        if (!((Number.isInteger(concurrency) || concurrency === Infinity) && concurrency > 0)) {
                return Promise.reject(new TypeError('Expected `concurrency` to be a number from 1 and up'));
        }

        const queue = [];
        let activeCount = 0;

        const next = () => {
                activeCount--;

                if (queue.length > 0) {
                        queue.shift()();
                }
        };

        const run = (fn, resolve, ...args) => {
                activeCount++;

                const result = pTry(fn, ...args);

                resolve(result);

                result.then(next, next);
        };

        const enqueue = (fn, resolve, ...args) => {
                if (activeCount < concurrency) {
                        run(fn, resolve, ...args);
                } else {
                        queue.push(run.bind(null, fn, resolve, ...args));
                }
        };

        const generator = (fn, ...args) => new Promise(resolve => enqueue(fn, resolve, ...args));
        Object.defineProperties(generator, {
                activeCount: {
                        get: () => activeCount
                },
                pendingCount: {
                        get: () => queue.length
                },
                clearQueue: {
                        value: () => {
                                queue.length = 0;
                        }
                }
        });

        return generator;
};

module.exports = pLimit;
module.exports.default = pLimit;