let { SerialPort } = require('serialport');

function open(device, baud)
{
    let serialPortOptions = {
        dataBits: 8,
        stopBits: 1,
        parity: 'none',
        baudRate: baud,
        path: device,
    };

    return new Promise((resolve, reject) => {
        let port = new SerialPort(serialPortOptions, function(err) {
            if (err)
                reject(err);
            else
                resolve(port);
        });
    });
        
}

function drain(port)
{
    // Drain port
    return new Promise((resolve, reject) => {
        port.drain((function(err) {
            if (err)
                reject(err);
            else
                resolve();
        }));
    });    
}

function close(port)
{
    return new Promise((resolve, reject) => {
        port.close(function(err) { 
            if (err)
                reject(err);
            else
                resolve();
        });
    })
}

function onDataHandler(data)
{
    console.log("On Data");
}

(async function() {

    // Open port
    console.log("Opening...");
    let port = await open("/dev/ttyUSB0", 115200);
    console.log("OK");

    // Data handler
    port.on('data', onDataHandler);
    port.off('data', onDataHandler);

    // Drain
    console.log("Draining");
    await drain(port);
    console.log("OK");

    // Close
    console.log("Closing");
    await close(port);
    console.log("OK");

    // PROBLEM 1: Process never exits.
    // Remove "data handler" or "drain" calls above, problem doesn't happen


    // PROBLEM 2: (possibly same issue) attempting to re-open the port fails with 
    // "[Error: Error Resource temporarily unavailable Cannot lock port]"

    // Open again...
    /*
    console.log("Opening (again)...");
    port = await open("/dev/ttyUSB0", 115200);
    console.log("OK");
    */

})();