callbag-combine

/**
* callbag-combine
* ---------------
*
* Callbag factory that combines the latest data points from multiple (2 or
* more) callbag sources. It delivers those latest values as an array. Works
* with both pullable and listenable sources.
*
* npm install callbag-combine
*
* Example:
*
* const interval = require('callbag-interval');
* const observe = require('callbag-observe');
* const combine = require('callbag-combine');
*
* const source = combine(interval(100), interval(350));
*
* observe(x => console.log(x))(source); // [2,0]
* // [3,0]
* // [4,0]
* // [5,0]
* // [6,0]
* // [6,1]
* // [7,1]
* // [8,1]
* // ...
*/

const EMPTY = {};

const combine = (...sources) => (start, sink) => {
if (start !== 0) return;
const n = sources.length;
if (n === 0) {
sink(0, () => {});
sink(1, []);
sink(2);
return;
}
let Ns = n; // start counter
let Nd = n; // data counter
let Ne = n; // end counter
const vals = new Array(n);
const sourceTalkbacks = new Array(n);
const talkback = (t, d) => {
if (t === 0) return;
for (let i = 0; i < n; i++) sourceTalkbacksi;
};
sources.forEach((source, i) => {
vals[i] = EMPTY;
source(0, (t, d) => {
if (t === 0) {
sourceTalkbacks[i] = d;
if (--Ns === 0) sink(0, talkback);
} else if (t === 1) {
const _Nd = !Nd ? 0 : vals[i] === EMPTY ? --Nd : Nd;
vals[i] = d;
if (_Nd === 0) {
const arr = new Array(n);
for (let j = 0; j < n; ++j) arr[j] = vals[j];
sink(1, arr);
}
} else if (t === 2) {
if (--Ne === 0) sink(2);
} else {
sink(t, d);
}
});
});
};

module.exports = combine;