callbag-concat

'use strict';

/**
* callbag-concat
* --------------
*
* Callbag factory that concatenates the data from multiple (2 or more)
* callbag sources. It starts each source at a time: waits for the previous
* source to end before starting the next source. Works with both pullable
* and listenable sources.
*
* npm install callbag-concat
*
* Example:
*
* const fromIter = require('callbag-from-iter');
* const iterate = require('callbag-iterate');
* const concat = require('callbag-concat');
*
* const source = concat(fromIter([10,20,30]), fromIter(['a','b']));
*
* iterate(x => console.log(x))(source); // 10
* // 20
* // 30
* // a
* // b
*/

const UNIQUE = {};

const concat = (...sources) => (start, sink) => {
if (start !== 0) return;
const n = sources.length;
if (n === 0) {
sink(0, () => {});
sink(2);
return;
}
let i = 0;
let sourceTalkback;
let lastPull = UNIQUE;
const talkback = (t, d) => {
if (t === 1) lastPull = d;
sourceTalkback(t, d);
};
(function next() {
if (i === n) {
sink(2);
return;
}
sourcesi => {
if (t === 0) {
sourceTalkback = d;
if (i === 0) sink(0, talkback);
else if (lastPull !== UNIQUE) sourceTalkback(1, lastPull);
} else if (t === 2 && d) {
sink(2, d);
} else if (t === 2) {
i++;
next();
} else {
sink(t, d);
}
});
})();
};

module.exports = concat;