Pausable duration countdown

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<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <meta
      http-equiv="Content-Security-Policy"
      content="default-src 'none'; style-src 'unsafe-inline'; script-src 'unsafe-inline'; img-src data: blob:; connect-src 'none'; form-action 'none'; object-src 'none'; base-uri 'none'"
    />
    <title>Make a little space. | MRHTML example</title>
    <style>
      :root {
        color-scheme: light;
        --paper: #f5f3ee;
        --surface: #fff;
        --ink: #172a3b;
        --muted: #536575;
        --line: #d2dce1;
        --blue: #234ed8;
        --soft: #eef3ff;
        --orange: #ad4b17;
        --error: #a62440;
        font:
          16px/1.6 system-ui,
          -apple-system,
          BlinkMacSystemFont,
          'Segoe UI',
          sans-serif;
        color: var(--ink);
        background: var(--paper);
      }
      * {
        box-sizing: border-box;
      }
      body {
        margin: 0;
        padding: clamp(24px, 6vw, 64px) 22px;
        min-height: 100svh;
      }
      main {
        width: min(760px, 100%);
        margin: auto;
        min-width: 0;
      }
      h1,
      h2,
      h3,
      p {
        margin: 0;
      }
      h1 {
        font-size: clamp(2rem, 6vw, 3rem);
        line-height: 1.08;
        letter-spacing: -0.055em;
        font-weight: 680;
        max-width: 680px;
      }
      h2 {
        font-size: 1.2rem;
        line-height: 1.3;
        letter-spacing: -0.02em;
      }
      p {
        color: var(--muted);
      }
      header {
        margin-bottom: 28px;
      }
      .brand {
        font:
          700 0.73rem/1.5 ui-monospace,
          monospace;
        letter-spacing: 0.1em;
        text-transform: uppercase;
        color: var(--blue);
        margin-bottom: 20px;
      }
      .intro {
        max-width: 62ch;
        margin-top: 16px;
      }
      .surface {
        background: var(--surface);
        border: 1px solid var(--line);
        border-radius: 18px;
        padding: clamp(20px, 4vw, 32px);
      }
      .note {
        font-size: 0.85rem;
        margin-top: 20px;
      }
      .eyebrow {
        font:
          600 0.72rem/1.5 ui-monospace,
          monospace;
        letter-spacing: 0.08em;
        text-transform: uppercase;
      }
      .actions {
        display: flex;
        flex-wrap: wrap;
        gap: 10px;
        margin-top: 20px;
      }
      button,
      input,
      textarea,
      select {
        font: inherit;
      }
      button {
        border: 1px solid var(--ink);
        background: var(--ink);
        color: #fff;
        border-radius: 8px;
        padding: 10px 17px;
        min-height: 44px;
        font-weight: 650;
        cursor: pointer;
      }
      button.secondary {
        background: transparent;
        color: var(--ink);
        border-color: var(--line);
      }
      button:hover:not(:disabled) {
        background: var(--blue);
        border-color: var(--blue);
        color: #fff;
      }
      button:disabled {
        cursor: not-allowed;
        opacity: 0.55;
      }
      label {
        font-weight: 600;
      }
      input:not([type='checkbox']):not([type='range']):not([type='file']),
      textarea,
      select {
        width: 100%;
        min-width: 0;
        border: 1px solid #8e9faa;
        border-radius: 8px;
        padding: 10px 12px;
        background: #fff;
        color: var(--ink);
      }
      textarea {
        resize: vertical;
        min-height: 180px;
      }
      input[type='range'] {
        width: 100%;
        accent-color: var(--blue);
      }
      input[type='checkbox'] {
        width: 20px;
        height: 20px;
        accent-color: var(--blue);
      }
      :focus-visible {
        outline: 3px solid var(--orange);
        outline-offset: 4px;
      }
      a {
        color: var(--blue);
      }
      .status {
        min-height: 1.6em;
        font-size: 0.9rem;
        margin-top: 18px;
        overflow-wrap: anywhere;
      }
      .status[data-error='true'] {
        color: var(--error);
      }
      [hidden] {
        display: none !important;
      }
      .sr-only {
        position: absolute;
        width: 1px;
        height: 1px;
        padding: 0;
        margin: -1px;
        overflow: hidden;
        clip: rect(0, 0, 0, 0);
        white-space: nowrap;
        border: 0;
      }
      .field {
        display: grid;
        gap: 7px;
        margin-top: 16px;
      }
      footer {
        font-size: 0.75rem;
        color: var(--muted);
        border-top: 1px solid var(--line);
        margin-top: 30px;
        padding-top: 16px;
        display: flex;
        justify-content: space-between;
        gap: 12px;
      }
      noscript {
        display: block;
        padding: 14px;
        background: #fff2d9;
        border: 1px solid #ad4b17;
        margin-top: 20px;
        border-radius: 8px;
        color: var(--ink);
      }
      @media (max-width: 400px) {
        body {
          padding: 25px 16px;
        }
        .surface {
          padding: 20px;
        }
        button {
          padding: 10px 14px;
        }
      }
      @media (prefers-reduced-motion: reduce) {
        *,
        *::before,
        *::after {
          scroll-behavior: auto !important;
          animation: none !important;
          transition: none !important;
        }
      }

      .timer-surface {
        background: var(--ink);
        color: #fff;
        border-radius: 20px;
        padding: clamp(25px, 5vw, 45px);
        text-align: center;
      }
      .timer-surface p {
        color: #d4e0e8;
      }
      #time-left {
        font:
          500 clamp(4rem, 16vw, 7.2rem)/1.2 ui-monospace,
          monospace;
        letter-spacing: -0.08em;
        margin: 25px 0 5px;
        font-variant-numeric: tabular-nums;
      }
      .duration-row {
        display: flex;
        justify-content: center;
        align-items: center;
        flex-wrap: wrap;
        gap: 14px;
        margin-top: 30px;
        font-size: 0.9rem;
      }
      #duration {
        width: 110px;
        text-align: center;
      }
      #duration-help {
        font-size: 0.75rem;
        margin-top: 8px;
      }
      .timer-surface .actions {
        justify-content: center;
        margin-top: 28px;
      }
      .timer-surface button {
        background: #d7ed9c;
        color: #1d2f23;
        border-color: #d7ed9c;
      }
      .timer-surface button.secondary {
        background: transparent;
        color: #fff;
        border-color: #8e9faa;
      }
      .timer-surface .status[data-error='true'] {
        color: #ffc1cb;
      }
    </style>
  </head>
  <body>
    <main>
      <header>
        <p class="brand">MRHTML / Runnable example</p>
        <h1>Make a little space.</h1>
        <p class="intro">
          A timer for a short reading, stretching or thinking break. You choose
          when it starts and stops.
        </p>
      </header>
      <section class="timer-surface">
        <p class="eyebrow">Your time, at your pace</p>
        <div
          id="time-left"
          role="timer"
          aria-live="off"
          aria-label="Time remaining"
        >
          01:30
        </div>
        <p id="timer-state">Ready when you are.</p>
        <div class="duration-row">
          <label for="duration">Duration in seconds</label
          ><input
            id="duration"
            type="number"
            min="1"
            max="3600"
            step="1"
            value="90"
            disabled
            aria-describedby="duration-help"
          />
        </div>
        <p id="duration-help">Choose a whole number from 1 to 3600.</p>
        <div class="actions">
          <button id="start-timer" type="button" disabled>Start timer</button
          ><button id="pause-timer" class="secondary" type="button" disabled>
            Pause</button
          ><button id="reset-timer" class="secondary" type="button" disabled>
            Reset
          </button>
        </div>
        <p id="timer-status" class="status" role="status" aria-atomic="true">
          The timer has not started.
        </p>
      </section>
      <p class="note">
        Time continues while this tab is in the background. Pause preserves the
        remaining duration. There is no sound, deadline offer or automatic
        action when time finishes. This duration demo uses the device clock;
        changing that clock can change the remaining time.
      </p>
      <noscript
        >The content is readable without JavaScript. Interactive controls are
        unavailable.</noscript
      >
      <footer>
        <span>MRHTML example</span><span>Original code · MIT</span>
      </footer>
    </main>
    <script>
      'use strict';
      (() => {
        const input = document.querySelector('#duration'),
          start = document.querySelector('#start-timer'),
          pause = document.querySelector('#pause-timer'),
          reset = document.querySelector('#reset-timer'),
          display = document.querySelector('#time-left'),
          state = document.querySelector('#timer-state'),
          status = document.querySelector('#timer-status');
        let remaining = 90000,
          deadline = 0,
          running = false,
          completed = false,
          timer = 0;
        const announce = (text, error = false) => {
          status.textContent = text;
          status.dataset.error = String(error);
        };
        function validDuration() {
          const value = Number(input.value);
          if (!Number.isInteger(value) || value < 1 || value > 3600) {
            announce('Enter a whole number of seconds from 1 to 3600.', true);
            input.focus();
            return null;
          }
          return value * 1000;
        }
        function render() {
          const seconds = Math.ceil(Math.max(0, remaining) / 1000);
          display.textContent = `${String(Math.floor(seconds / 60)).padStart(2, '0')}:${String(seconds % 60).padStart(2, '0')}`;
          pause.disabled = !running;
          start.disabled = running;
          input.disabled = running;
          start.textContent = completed
            ? 'Start again'
            : remaining < Number(input.value) * 1000
              ? 'Resume'
              : 'Start timer';
        }
        function finish() {
          if (completed) return;
          completed = true;
          running = false;
          remaining = 0;
          clearTimeout(timer);
          state.textContent = 'Your time is complete.';
          announce('Timer complete. Take the next step when you are ready.');
          render();
        }
        function tick() {
          clearTimeout(timer);
          if (!running) return;
          remaining = Math.max(0, deadline - Date.now());
          if (remaining === 0) {
            finish();
            return;
          }
          render();
          if (!document.hidden) timer = setTimeout(tick, 200);
        }
        start.addEventListener('click', () => {
          if (running || validDuration() === null) return;
          if (completed) {
            const duration = validDuration();
            if (duration === null) return;
            remaining = duration;
            completed = false;
          }
          if (remaining <= 0) return;
          running = true;
          deadline = Date.now() + remaining;
          state.textContent = 'A little time for yourself.';
          announce('Timer running.');
          tick();
        });
        pause.addEventListener('click', () => {
          if (!running) return;
          remaining = Math.max(0, deadline - Date.now());
          if (!remaining) {
            finish();
            return;
          }
          running = false;
          clearTimeout(timer);
          state.textContent = 'Paused. Come back when you are ready.';
          announce('Timer paused.');
          render();
        });
        function setDuration() {
          if (running) return;
          const value = validDuration();
          if (value === null) return;
          remaining = value;
          completed = false;
          state.textContent = 'Ready when you are.';
          announce('Duration updated. The timer has not started.');
          render();
        }
        input.addEventListener('change', setDuration);
        reset.addEventListener('click', () => {
          clearTimeout(timer);
          running = false;
          input.disabled = false;
          const value = validDuration();
          remaining = value === null ? 90000 : value;
          if (value === null) input.value = '90';
          completed = false;
          state.textContent = 'Ready when you are.';
          announce('Timer reset.');
          render();
        });
        document.addEventListener('visibilitychange', () => {
          if (running) tick();
        });
        input.disabled = false;
        start.disabled = false;
        reset.disabled = false;
        render();
      })();
    </script>
  </body>
</html>