BangleApps/apps/metronome/metronome.js

var tStart = Date.now();
var cindex=0;  // index to iterate through colous
var bpm=60;  // ininital bpm value
var time_diffs = [1000, 1000, 1000];  //array to calculate mean bpm
var tindex=0;  //index to iterate through time_diffs


Bangle.setLCDTimeout(undefined);  //do not deaktivate display while running this app

const storage = require("Storage");
const SETTINGS_FILE = 'metronome.settings.json';

//return setting
function setting(key) {
  //define default settings
  const DEFAULTS = {
    'beatsperbar': 4,
    'buzzintens': 0.75,
  };
  if (!settings) { loadSettings(); }
  return (key in settings) ? settings[key] : DEFAULTS[key];
}

//load settings
let settings;

function loadSettings() {
  settings = storage.readJSON(SETTINGS_FILE, 1) || {};
}

function changecolor() {
  const colors = {
    0: { value: 0xF800, name: "Red" },
    1: { value: 0xFFFF, name: "White" },
    2: { value: 0x9492, name: "gray" },
    3: { value: 0xFFFF, name: "White" },
    4: { value: 0x9492, name: "gray" },
    5: { value: 0xFFFF, name: "White" },
    6: { value: 0x9492, name: "gray" },
    7: { value: 0xFFFF, name: "White" },
  };
  g.setColor(colors[cindex].value);
  if (cindex == setting('beatsperbar')-1) {
    cindex = 0;
  }
  else {
    cindex += 1;
  }
  return cindex;
}

function updateScreen() {
  g.reset().clearRect(0, 50, 250, 150);
  changecolor();
  try {
    Bangle.buzz(50, setting('buzzintens'));
  } catch(err) {
  }
  g.setFont("Vector",40).setFontAlign(0,0);
  g.drawString(Math.floor(bpm)+"bpm", g.getWidth()/2, 100);
}

Bangle.on('touch', function(button) {
// setting bpm by tapping the screen. Uses the mean time difference between several tappings.
  if (tindex < time_diffs.length) {
    if (Date.now()-tStart < 5000) {
      time_diffs[tindex] = Date.now()-tStart;
    }
  } else {
    tindex=0;
    time_diffs[tindex] = Date.now()-tStart;
  }
  tindex += 1;
  mean_time = 0.0;
  for(count = 0; count < time_diffs.length; count++) {
    mean_time += time_diffs[count];
  }
  time_diff = mean_time/count;

  tStart = Date.now();
  clearInterval(time_diff);
  bpm = (60 * 1000/(time_diff));
  updateScreen();
  clearInterval(interval);
  interval = setInterval(updateScreen, 60000 / bpm);
  return bpm;
});

// enable bpm finetuning via buttons.
setWatch(() => {
  bpm += 1;
  clearInterval(interval);
  interval = setInterval(updateScreen, 60000 / bpm);
}, BTN1, {repeat:true});

setWatch(() => {
  if (bpm > 1) {
    bpm -= 1;
    clearInterval(interval);
    interval = setInterval(updateScreen, 60000 / bpm);
  }
}, BTN3, {repeat:true});

interval = setInterval(updateScreen, 60000 / bpm);

g.clear(1).setFont("6x8");
g.drawString('Touch the screen to set tempo.\nUse BTN1 to increase, and\nBTN3 to decrease bpm value by 1.', 25, 200);

Bangle.loadWidgets();
Bangle.drawWidgets();