Tabs Slide Indicator

<!--
  Tabs Slide Indicator - transitions.dev-inspired primitive for HyperFrames.

  Paste the markup, CSS and script into a composition. Use the timeline
  integration note at the bottom as the starting point for deterministic GSAP
  animation.

  Variables. The script reads each one, falls back to the declared default on
  anything missing or unrecognised, and writes the result as a custom property
  the CSS below consumes. The timeline recipe at the bottom is untouched by
  them: it keeps sliding the pill one tab to the right, and these decide how
  wide that tab is, what the pill looks like and what the tabs say.

    - accent (ink | green | blue | violet, default ink): fill of the sliding
      pill. ink is a literal near-black; the other three ride the composition's
      own brand, accent and accent-2 tokens and fall back to that same ink when
      the composition declares none. The labels sitting on it stay white, so all
      four keep the active tab readable.
    - width (compact | standard | wide, default standard): width of one tab,
      72px, 86px or 104px. The slide the timeline drives is scaled by the same
      ratio, so the pill still lands exactly on the next tab rather than
      stopping short or overshooting it.
    - shape (pill | rounded | square, default pill): corner radius of the track
      and the pill, 999px, 12px or 4px.
    - labels (text, default "Plan,Debug,Ask"): the tab names, separated by
      commas. Two or more names rebuild the row, one name or none leaves the
      authored markup alone, since a single tab has nowhere to slide to.

  On every default the result is identical to the original: three 86px tabs in
  a light pill track, a near-black pill sliding from the first to the second.
-->

<div
  class="hf-transition-tabs-slide-indicator"
  data-composition-variables='[
    { "id": "accent", "type": "enum", "role": "style", "label": "Accent", "description": "Fill of the sliding pill. ink is literal; the rest ride the composition theme tokens.", "default": "ink", "options": [{ "value": "ink", "label": "Ink" }, { "value": "green", "label": "Green" }, { "value": "blue", "label": "Blue" }, { "value": "violet", "label": "Violet" }] },
    { "id": "width", "type": "enum", "role": "layout", "label": "Tab width", "description": "Width of one tab. The slide the timeline drives is scaled to match, so the pill still lands on the next tab.", "default": "standard", "options": [{ "value": "compact", "label": "Compact" }, { "value": "standard", "label": "Standard" }, { "value": "wide", "label": "Wide" }] },
    { "id": "shape", "type": "enum", "role": "style", "label": "Shape", "description": "Corner radius of the track and the pill.", "default": "pill", "options": [{ "value": "pill", "label": "Pill" }, { "value": "rounded", "label": "Rounded" }, { "value": "square", "label": "Square" }] },
    { "id": "labels", "type": "string", "role": "content", "label": "Labels", "description": "The tab names, separated by commas. Two or more names rebuild the row.", "default": "Plan,Debug,Ask" }
  ]'
>
  <span class="indicator"></span><button>Plan</button><button>Debug</button><button>Ask</button>
</div>

<style>
  .hf-transition-tabs-slide-indicator {
    --hf-tab-x: 0px;
    position: relative;
    display: inline-grid;
    grid-template-columns: repeat(var(--hf-tab-count, 3), var(--hf-tab-width, 86px));
    padding: 4px;
    border: 1px solid #e4e4e7;
    border-radius: var(--hf-tab-radius, 999px);
    background: #f4f4f5;
    font-family: Inter, system-ui, sans-serif;
  }
  .hf-transition-tabs-slide-indicator .indicator {
    position: absolute;
    top: 4px;
    left: 4px;
    width: var(--hf-tab-width, 86px);
    height: 36px;
    border-radius: var(--hf-tab-radius, 999px);
    background: var(--hf-tab-fill, #18181b);
    transform: translateX(calc(var(--hf-tab-x) * var(--hf-tab-step, 1)));
    box-shadow: 0 12px 26px rgba(0, 0, 0, 0.18);
  }
  .hf-transition-tabs-slide-indicator button {
    position: relative;
    z-index: 1;
    height: 36px;
    border: 0;
    background: transparent;
    color: #71717a;
    font-weight: 850;
  }
  .hf-transition-tabs-slide-indicator button:nth-of-type(2) {
    color: #fff;
  }
</style>

<script>
  (function () {
    "use strict";

    var vars =
      window.__hyperframes && window.__hyperframes.getVariables
        ? window.__hyperframes.getVariables()
        : {};

    // Unrecognised overrides return to their declared defaults.
    // The pill is the one accent-carrying element here, so the three chromatic
    // options ride the composition's own tokens and fall back to ink.
    var accents = {
      ink: "#18181b",
      green: "var(--brand, #18181b)",
      blue: "var(--accent, #18181b)",
      violet: "var(--accent-2, #18181b)",
    };
    var widths = { compact: 72, standard: 86, wide: 104 };
    var shapes = { pill: "999px", rounded: "12px", square: "4px" };

    function pick(table, value, fallback) {
      return Object.prototype.hasOwnProperty.call(table, value) ? value : fallback;
    }

    var accent = accents[pick(accents, vars.accent, "ink")];
    var width = widths[pick(widths, vars.width, "standard")];
    var radius = shapes[pick(shapes, vars.shape, "pill")];
    var labels =
      typeof vars.labels === "string"
        ? vars.labels.split(",").map(function (part) {
            return part.trim();
          })
        : [];
    labels = labels.filter(function (part) {
      return part.length > 0;
    });

    var roots = document.querySelectorAll(".hf-transition-tabs-slide-indicator");
    for (var i = 0; i < roots.length; i += 1) {
      roots[i].style.setProperty("--hf-tab-fill", accent);
      roots[i].style.setProperty("--hf-tab-width", width + "px");
      // The timeline slides the pill by one standard tab, so scale that slide
      // to whatever a tab is actually worth here.
      roots[i].style.setProperty("--hf-tab-step", String(width / 86));
      roots[i].style.setProperty("--hf-tab-radius", radius);
      // A single tab has nowhere to slide to, so it is left as authored.
      if (labels.length > 1) {
        var old = roots[i].querySelectorAll("button");
        for (var j = 0; j < old.length; j += 1) {
          old[j].parentNode.removeChild(old[j]);
        }
        for (var k = 0; k < labels.length; k += 1) {
          var button = document.createElement("button");
          button.textContent = labels[k];
          roots[i].appendChild(button);
        }
        roots[i].style.setProperty("--hf-tab-count", String(labels.length));
      }
    }
  })();
</script>

<!--
  Timeline integration:
  tl.fromTo('.hf-transition-tabs-slide-indicator .indicator', { '--hf-tab-x': '0px' }, { '--hf-tab-x': '86px', duration: 0.42, ease: 'power3.inOut' }, startTime);
-->