concept2/lib/concept2.js

HID library for communicating with Concept2 performance monitor modules.

'use strict'

const _ = require('lodash')
const HID = require('node-hid')
const EventEmitter = require('events')
const Frame = require('csafe').Frame
const FrameReader = require('csafe').FrameReader

/**
 * Concept2 HID Event Library
 * 
 * Provides communication with a connected Concept2
 * HID-compliant performance monitor via the CSAFE
 * communication protocol. 
 * 
 * @param {int} index - the index of the device to use. 
 *  Consult the output of `lsusb`.
 */
class Concept2 extends EventEmitter {

  constructor(index = 0) {
    super()
    this.VENDOR_ID = 6052
    this.devices = this.getDevices()
    this.frameReader = new FrameReader
    this.frameCount = 0

    if (!this.devices.length) {
      throw new Error("No Concept2 devices found.")
    }

    this.hid = new HID.HID(this.devices[index].path)
    this.hid.on('data', this.emitData.bind(this))
    this.frameReader.on('frame', this.emitFrame.bind(this))    
  }

  /**
   * Returns a list of connected Concept2 devices.
   */
  getDevices() {
    let allDevices = HID.devices()
    return _.filter(allDevices, { vendorId: this.VENDOR_ID })
  }

  /**
   * Event handler for new response data from the
   * underlying HID.
   */
  emitData(record) {
    let buffer = record.slice(1)
    
    this.emit('data', buffer)
    this.frameReader.read(buffer)
  }

  /**
   * Event handler for a new CSAFE frame.
   */
  emitFrame(frame) {
    this.frameCount++
    this.emit('frame', frame)
  }

  /**
   * Generic read callback for the HID.
   * 
   * @param {function} callback - data handler callback.   
   */
  read(callback) {
    this.hid.read(callback)
  }

  /**
   * Write an array or buffer to the HID.
   * 
   * @param {Buffer|Frame} data - the data to write. 
   * @param {integer} recordId - the recordId to associate
   *  this write request with.
   */
  write(data, recordId = 1) {
    let buffer = Buffer.alloc(22)
    
    // For convienience, extract the buffer if a Frame is passed.
    if (data instanceof Frame) {
      data = data.buffer
    }

    // Write the recordId and copy in the data buffer.
    buffer.writeInt8(recordId)
    data.copy(buffer, 1)

    // Write to the device.
    this.hid.write(Array.from(buffer))
  }
}

module.exports = Concept2