// async.eachLimit：
import { eachLimit } from 'async';
import sleep from './sleep';

let times = [100, 150, 200, 250, 300];

console.log('sleep start');
console.time('async with concurrency');
eachLimit(times, 2, sleep, (err) => {
    console.timeEnd('async with concurrency');
    console.log('sleep complete');
});

// Promise.map
import Promise from 'bluebird';
import sleep from './sleep';

let times = [100, 150, 200, 250, 300];

console.log('sleep start');
console.time('promise one by one');
Promise.map(times, (time) => {
    return sleep(time);
}, {
    concurrency: 2
}).then(() => {
    console.timeEnd('promise one by one');
    console.log('sleep complete');
});

// ES7 async/await：
import sleep from './sleep';

let times = [100, 150, 200, 250, 300];

(async function() {
    console.log('sleep start');
    console.time('es7 with concurrency');
    await pool(2, async () => {
        await sleep(times.shift());
        return times.length > 0;
    });
    console.timeEnd('es7 with concurrency');
    console.log('sleep complete');
}());

async function pool(size, task) {
    var active = 0;
    var done = false;
    var errors = [];
    return new Promise((resolve, reject) => {
        next();
        function next() {
            while (active < size && !done) {
                active += 1;
                task()
                    .then(more => {
                        if (--active === 0 && (done || !more))
                            errors.length === 0 ? resolve() : reject(errors);
                        else if (more)
                            next();
                        else
                            done = true;
                    })
                    .catch(err => {
                        errors.push(err);
                        done = true;
                        if (--active === 0)
                            reject(errors);
                    });
            }
        }
    });
}