"use strict";

const Promise = require("bluebird");
const pipe = require("@promistream/pipe");
const rangeNumbers = require("@promistream/range-numbers");
const map = require("@promistream/map");
const collect = require("@promistream/collect");
const buffer = require("./");

function duplicateEven() {
	return pipe([
		map((value) => {
			if (value % 2 === 0) {
				return [value, value];
			} else {
				return [];
			}
		}),
		buffer()
	]);
}

return Promise.try(() => {
	return pipe([
		rangeNumbers(0, 20),
		duplicateEven(),
		collect()
	]).read();
}).then((result) => {
	console.log(result);
	// [ 0, 0, 2, 2, 4, 4, 6, 6, 8, 8, 10, 10, 12, 12, 14, 14, 16, 16, 18, 18 ]
});