const { spawn } = require("child_process");
const { Readable, Duplex, Writable } = require("stream");

const wrapRS = txt => {
    const r = new Readable();
    r._read = () => {
        r.push(txt);
        r.push(null);
    };
    return r;
};

const promiseWriter = fn => {
    const w = new Writable();
    w._write = (chunk, _, next) => {
        fn(chunk.toString());
        // write only once
        w.destroy();
    };
    return w;
};

const Node = () => {
    const d = new Duplex();
    const proc = spawn("node");
    proc.stdout.on("data", chunk => d.push(chunk));
    proc.stdout.on("end", () => d.push(null));
    d._write = (chunk, _, next) => {
        proc.stdin.write(chunk);
        next();
    };
    d._read = () => undefined;
    d.on("finish", () => proc.stdin.end());
    return d;
};

const evalCode = code => {
    return new Promise(resolve => {
        wrapRS(code)
            .pipe(Node())
            .pipe(promiseWriter(resolve));
    });
};

// TESTING TIME
const testObject = {
    a: 1,
    b: { c: 1, d: 1 },
    d: [1, 2, 3, 4, 5]
};

evalCode("console.log(1212)").then(x => console.log(x));
// 1212
evalCode(`console.log(${JSON.stringify(testObject)})`).then(x => console.log(x));
// { a: 1, b: { c: 1, d: 1 }, d: [ 1, 2, 3, 4, 5 ] }