const batteryLevel = batteryPercent => ({
  "-2": "not connected",
  "-1": "charging"
})[batteryPercent] ?? batteryPercent + "%";

const batteryIcon = batteryPercent => ({
  "-2": "action-unavailable",
  "-1": "battery-ac-adapter"
})[batteryPercent] ?? "audio-headphones-symbolic";

const interpolateColor = (c0, c1, f) => { // https://stackoverflow.com/a/63775249
  if(isNaN(f)) return "transparent";
  c0 = c0.replace('#', '').match(/.{1,2}/g).map(oct => parseInt(oct, 16) * (1-f));
  c1 = c1.replace('#', '').match(/.{1,2}/g).map(oct => parseInt(oct, 16) * f);
  return "#" + [0, 1, 2]
    .map(i => Math.min(Math.round(c0[i] + c1[i]), 255))
    .reduce((a, v) => ((a << 8) + v), 0)
    .toString(16)
    .padStart(6, "0");
};