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  <!DOCTYPE html>
<html lang="en">
<head>
  <title>Timer</title>
  <meta charset="utf-8" />
  <meta name="description" content="Minute precision timer.">
  <meta name="viewport" content="width=device-width, initial-scale=1" />
</head>
<body>
  <audio src="432.mp3" id="beep" autostart="false"></audio>
  <style>
    :root {
      color-scheme: light dark;
      /* DARK THEME */
      --dark-main-bg-color: 0, 0, 0;
      --dark-text-color: 240, 240, 240;
      /* LIGHT THEME */
      --light-main-bg-color: 255, 255, 255;
      --light-text-color: 0, 0, 0;
      /* CHOOSE DARK THEME */
      --main-bg-color: rgb(var(--dark-main-bg-color));
      --text-color: rgb(var(--dark-text-color));
    }
    /* CHOOSE LIGHT THEME */
    @media (prefers-color-scheme: light) {
      :root {
        --main-bg-color: rgb(var(--light-main-bg-color));
        --text-color: rgb(var(--light-text-color));
      }
    }
    body {
      background: var(--main-bg-color);
      color: var(--text-color);
    }
  </style>
  <div style='display: flex; align-items: center;'>
  <button autofocus id="toggle" style='min-width: 50px'>Start</button>
  <input type="range" min="1" max="120" value="20" id="range">
  <label for="range"><span id='numMinutes'>20</span> minutes</label>
  </div>
  <div id='remaining' style='visibility:hidden;'>Time Left: <span id='minutesLeft'>20</span>:<span id='secondsLeft'>00</span></div>
  <script>
  (function() {
  var getEl = document.getElementById.bind(document); 
  var DOM = {
    // audio element
    beep:       getEl('beep'),
    // top UI
    toggle:      getEl('toggle'),
    range:       getEl('range'),
    numMinutes:  getEl('numMinutes'),
    // Time remaining UI
    remaining:   getEl('remaining'),
    minutesLeft: getEl('minutesLeft'),
    secondsLeft: getEl('secondsLeft'),
  }
  var state = {
    remaining: 0,
    counting: false,
    interval: 0,
  }
  var updateInterval = 5 // in seconds
  function updateRemaining(secondsRemaining) {
    state.remaining = secondsRemaining
    DOM.minutesLeft.innerHTML = Math.floor(secondsRemaining / 60)
    DOM.secondsLeft.innerHTML = (secondsRemaining % 60).toString().padStart(2, '0')
  }
  function start() {
    if (state.interval > 0) {
      clearInterval(state.interval)
      state.interval = 0
    }
    updateRemaining(DOM.range.value * 60)
    DOM.remaining.style.visibility = 'visible'
    DOM.toggle.innerHTML = 'Stop'
    state.counting = true
    DOM.range.disabled = true
    state.interval = setInterval(function () {
      updateRemaining(state.remaining - updateInterval)
      if (state.remaining <= 0) {
        DOM.beep.play()
        stop()
      }
    }, updateInterval * 1000)
  }
  function stop() {
    if (state.interval > 0) {
      clearInterval(state.interval)
      state.interval = 0
    }
    state.counting = false
    DOM.remaining.style.visibility = 'hidden'
    DOM.toggle.innerHTML = 'Start'
    DOM.range.disabled = false
  }
  DOM.toggle.addEventListener('click', () =>  state.counting ? stop() : start())
  DOM.range.addEventListener('change', (e) => {
    // if (state.counting) {
      // event.stopPropagation()
      // return false
    // }
    DOM.numMinutes.innerHTML = e.target.value
  })
  })()
  </script>
</body>
</html>