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// Read serial number of any RFID tags
// connected over serial to a reader


// The path to the serial port
// the card is connected to
var serialPath = process.env.SERIAL_PORT || '/dev/tty.SLAB_USBtoUART';

var debug = require('debug')('rfid:debug'),
    log   = console.log,
    serialport = require('serialport');

var Cmd = {
    start: 0xAA
  , ok   : 0x00
  , end  : 0xBB
};

var serial = new serialport.SerialPort(serialPath, {
  baudrate: 9600,
  parser: serialport.parsers.byteDelimiter(Cmd.end)
});

// MF_GET_SNR (0x25) command
// http://neophob.com/files/rfid/PROTOCOL-821-880%20_2_.pdf
var query = [Cmd.start, 0x00, 0x03, 0x25, 0x26, 0x00, 0x00, Cmd.end];

function hex(num) {
  return (num < 10 ) ? '0' + num : num.toString(16);
}

function hexString(array) {
  return array
    .map(hex)
    .join('');
}

var lastTagId = null;

// Prints the ID and keeps a reference
// to it since we're polling the reader
// for tags and don't want to repeatedly
// print the same id
function done(id) {
  if (id && lastTagId != id) {
    lastTagId = id;
    log('id', id);
  } else if (id == null && lastTagId != null) {
    lastTagId = null;
    log('Removed');
  }
  setTimeout(doQuery, 0);
}

// Parse a response from the reader,
// an array of bytes
function parseResponse(b) {
  var status = b[3],  // query success
      numTags = b[4], // how many tags found
      id = [];

  if (status == Cmd.ok) {
    debug('read: ok', b);

    debug(numTags);

    switch(numTags) {
      case 0x00: debug('one tag readable');
        break;
      case 0x01: debug('at least 2 tags readable');
        break;
    }

    id = b.slice(5, 9); // 4 bit device serial number
    debug('ID: ' + id);

    id = hexString(id); // turn the 4 bits into a hex string

    done(id);
  } else {
    done();
  }

}

// Write a query to the reader to
// find any tags within it's range
// This triggers data to be sent
// back over the serial port
function doQuery () {
  serial.write(query);
}

// On serial port open set up listener
// for incoming data and trigger
// done() to kick off polling
serial.on('open', function () {
  log('Connected');
  serial.on('data', parseResponse);
  done();
});