sensorFrequencia.js

/* 
    💓HRM Extension - Heart Rate Monitor
    Chrome Extension Project
    Projeto de uma extensão Chrome informando em tempo real a taxa de frequência cardiaca conectada via Bluetooth.
    Por Gustavo Kennedy Renkel
*/
(function() {
  'use strict';

  class HeartRateSensor {
    constructor() {
      this.device = null;
      this.server = null;
      this._characteristics = new Map();
    }
    connect() {
      return navigator.bluetooth.requestDevice({filters:[{services:[ 'heart_rate' ]}]})
      .then(device => {
        this.device = device;
        return device.gatt.connect();
      })
      .then(server => {
        this.server = server;
        return server.getPrimaryService('heart_rate');
      })
      .then(service => {
        return this._cacheCharacteristic(service, 'heart_rate_measurement');
      })
    }

    /* Serviço de Frequência Cardíaca */

    startNotificationsHeartRateMeasurement() {
      return this._startNotifications('heart_rate_measurement');
    }
    stopNotificationsHeartRateMeasurement() {
      return this._stopNotifications('heart_rate_measurement');
    }
    parseHeartRate(value) {
      // No Chrome 50+, o DataView é retornado no ArrayBuffer.
      value = value.buffer ? value : new DataView(value);
      let flags = value.getUint8(0);
      let rate16Bits = flags & 0x1;
      let result = {};
      let index = 1;
      if (rate16Bits) {
        result.heartRate = value.getUint16(index, /*littleEndian=*/true);
        index += 2;
      } else {
        result.heartRate = value.getUint8(index);
        index += 1;
      }
      let contactDetected = flags & 0x2;
      let contactSensorPresent = flags & 0x4;
      if (contactSensorPresent) {
        result.contactDetected = !!contactDetected;
      }
      let energyPresent = flags & 0x8;
      if (energyPresent) {
        result.energyExpended = value.getUint16(index, /*littleEndian=*/true);
        index += 2;
      }
      let rrIntervalPresent = flags & 0x10;
      if (rrIntervalPresent) {
        let rrIntervals = [];
        for (; index + 1 < value.byteLength; index += 2) {
          rrIntervals.push(value.getUint16(index, /*littleEndian=*/true));
        }
        result.rrIntervals = rrIntervals;
      }
      return result;
    }

    /* Utilitários */

    _cacheCharacteristic(service, characteristicUuid) {
      return service.getCharacteristic(characteristicUuid)
      .then(characteristic => {
        this._characteristics.set(characteristicUuid, characteristic);
      });
    }
    _readCharacteristicValue(characteristicUuid) {
      let characteristic = this._characteristics.get(characteristicUuid);
      return characteristic.readValue()
      .then(value => {
        // In Chrome 50+, a DataView is returned instead of an ArrayBuffer.
        value = value.buffer ? value : new DataView(value);
        return value;
      });
    }
    _writeCharacteristicValue(characteristicUuid, value) {
      let characteristic = this._characteristics.get(characteristicUuid);
      return characteristic.writeValue(value);
    }
    _startNotifications(characteristicUuid) {
      let characteristic = this._characteristics.get(characteristicUuid);
      // Retorna a característica para configurar o evento charactervaluechanged
      // manipuladores resolvidos em promise.
      return characteristic.startNotifications()
      .then(() => characteristic);
    }
    _stopNotifications(characteristicUuid) {
      let characteristic = this._characteristics.get(characteristicUuid);
      // Retorna a característica para remover o evento characteristicvaluechanged
      // manipuladores resolvidos em promise.
      return characteristic.stopNotifications()
      .then(() => characteristic);
    }
  }

  window.heartRateSensor = new HeartRateSensor();

})();