Easier to read charts for Health App

// test data 
//var data = new Uint16Array([1023, 1020, 5300, 3178, 1500, 10600, 5700, 1008, 5090, 1010, 6100, 712]);

// OR pull data from the health app
var data = new Uint16Array(31);
require("health").readDailySummaries(new­ Date(), h=>data[h.day]+=h.steps);

const w = g.getWidth();
const h = g.getHeight();

// find the max value in the array, using a loop due to array size 
function max(arr) {
  var m = -Infinity;

  for(var i=0; i< arr.length; i++)
    if(arr[i] > m) m = arr[i];
  return m;
}

// find the end of the data, the array might be for 31 days but only have 2 days in it
function get_data_length(arr) {
  var nlen = arr.length;
  
  for(var i = arr.length - 1; i > 0 && arr[i] == 0;  i--)
    nlen--;
  
  return nlen;
}

// choose initial index that puts the last day on the end
const len = get_data_length(data);
var index = Math.max(len - 5, -5);
const max_datum = max(data);  // find highest bar, for scaling

function draw() {
  const bar_bot = 140;
  const bar_width = (w - 2) / 9;  // we want 9 bars, bar 5 in the centre
  var bar_top;
  var bar;
  
  g.setColor(g.theme.bg);
  g.fillRect(0,24,w,h);
  
  for (bar = 1; bar < 10; bar++) {

    if (bar == 5) {
      g.setFont('6x8', 2);
      g.setFontAlign(0,-1)
      g.setColor(g.theme.fg);
      g.drawString("DAY " + (index + bar) + "   " + data[index + bar - 1], g.getWidth()/2, 150);
      g.setColor("#00f");
    } else {
      g.setColor("#0ff");
    }

    // draw a fake 0 height bar if index is outside the bounds of the array
    if ((index + bar - 1) >= 0 && (index + bar - 1) < len) 
      bar_top = bar_bot - 100 * (data[index + bar - 1]) / max_datum;
    else
      bar_top = bar_bot;

    g.fillRect( 1 + (bar - 1)* bar_width, bar_bot, 1 + bar*bar_width, bar_top);
    g.setColor(g.theme.fg);
    g.drawRect( 1 + (bar - 1)* bar_width, bar_bot, 1 + bar*bar_width, bar_top);
  }
}

function next() {
  index = Math.min(len - 5, index + 1);
  //console.log("next="+index);
}

function prev() {
  index = Math.max(-4, index - 1);
  //console.log("prev="+index);
}

Bangle.on('swipe', dir => {
  if (dir == 1) prev(); else next();
  draw();
});

// handle switch display on by pressing BTN1
Bangle.on('lcdPower', function(on) {
  if (on) draw();
});

draw();
Bangle.loadWidgets();
Bangle.drawWidgets();
Bangle.setUI("clock");  // returns to launcher for now