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'use strict';
const pTry = require('p-try');
module.exports = concurrency => {
if (concurrency < 1) {
throw 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));
}
};
return (fn, ...args) => new Promise(resolve => enqueue(fn, resolve, ...args));
};