Color Picker

<%# Markup for the color-picker demo.
    The library manages each channel's (hue / saturation / lightness) role="slider"
    value, composes them into a color two-way-synced with the hex input, and updates
    --stimeo-color for the preview. The 2D palette is decomposed into independent 1D
    sliders for accessibility. Thumb position and look are the consumer's CSS. %>
<div
  class="color-picker"
  data-controller="stimeo--color-picker"
  data-stimeo--color-picker-value-value="#3366cc">
  <div
    class="color-picker__preview"
    data-stimeo--color-picker-target="preview"
    aria-hidden="true"></div>

  <div class="color-picker__channels">
    <% { hue: [t("components.color_picker.demo.hue"), 360, 210],
         saturation: [t("components.color_picker.demo.saturation"), 100, 60],
         lightness: [t("components.color_picker.demo.lightness"), 100, 50] }
       .each do |channel, (label, max, now)| %>
      <div class="color-picker__channel">
        <span class="color-picker__channel-label"><%= label %></span>
        <div
          class="color-picker__track color-picker__track--<%= channel %>"
          role="slider"
          aria-label="<%= label %>"
          data-channel="<%= channel %>"
          tabindex="0"
          aria-valuemin="0"
          aria-valuemax="<%= max %>"
          aria-valuenow="<%= now %>"
          data-stimeo--color-picker-target="slider"
          data-action="
            keydown->stimeo--color-picker#onKeydown
            pointerdown->stimeo--color-picker#onPointerDown">
          <span class="color-picker__thumb" aria-hidden="true"></span>
        </div>
      </div>
    <% end %>
  </div>

  <label class="color-picker__hex">
    <span><%= t("components.color_picker.demo.hex") %></span>
    <input
      type="text"
      inputmode="text"
      aria-label="<%= t("components.color_picker.demo.hex") %>"
      value="#3366cc"
      data-stimeo--color-picker-target="hex"
      data-action="change->stimeo--color-picker#onHexInput" />
  </label>

  <input type="hidden" name="brand_color" data-stimeo--color-picker-target="field" />
</div>

/*
 * Presentation-only styles for the color-picker demo.
 * The library updates each slider's aria-valuenow / aria-valuetext, the hex value,
 * and --stimeo-color for the preview. The thumb position uses --stimeo-demo-pos,
 * which demo.js normalizes from aria-valuenow (an example of consumer-side styling).
 */

.color-picker {
  display: grid;
  gap: 0.85rem;
  max-width: 20rem;
}

.color-picker__preview {
  height: 3rem;
  border: 1px solid #cbd5e1;
  border-radius: 0.5rem;
  /* Show the current color the library exposes. */
  background: var(--stimeo-color, #000);
}

.color-picker__channels {
  display: grid;
  gap: 0.7rem;
}

.color-picker__channel {
  display: grid;
  gap: 0.25rem;
}

.color-picker__channel-label {
  font-size: 0.8rem;
  color: #475569;
}

.color-picker__track {
  position: relative;
  height: 0.85rem;
  border-radius: 0.5rem;
  cursor: pointer;
  touch-action: none;
}

.color-picker__track--hue {
  background: linear-gradient(
    to right,
    #f00 0%,
    #ff0 17%,
    #0f0 33%,
    #0ff 50%,
    #00f 67%,
    #f0f 83%,
    #f00 100%
  );
}

.color-picker__track--saturation {
  background: linear-gradient(to right, #808080, #2563eb);
}

.color-picker__track--lightness {
  background: linear-gradient(to right, #000, #2563eb, #fff);
}

.color-picker__thumb {
  position: absolute;
  top: 50%;
  /* The fraction the demo's demo.js computed from aria-valuenow. */
  left: var(--stimeo-demo-pos, 0%);
  width: 0.95rem;
  height: 0.95rem;
  transform: translate(-50%, -50%);
  border: 2px solid #fff;
  border-radius: 50%;
  box-shadow: 0 0 0 1px #334155;
  background: transparent;
}

.color-picker__track:focus-visible {
  outline: 2px solid var(--accent, #2563eb);
  outline-offset: 3px;
}

.color-picker__hex {
  display: grid;
  gap: 0.25rem;
  font-size: 0.8rem;
  color: #475569;
}

.color-picker__hex input {
  padding: 0.4rem 0.55rem;
  border: 1px solid #cbd5e1;
  border-radius: 0.4rem;
  font: inherit;
  font-family: ui-monospace, monospace;
}

// Demo that consumes the color-picker's values (consumer-side JS).
//
// The core controller (stimeo--color-picker) updates each slider's aria-valuenow /
// aria-valuetext, the hex value, and --stimeo-color for the preview, but does not
// provide the thumb position (the look). Here, on each change event, we normalize each
// slider's aria-valuenow to a fraction and reflect it as --stimeo-demo-pos for the
// thumb position (an example of consumer-side styling).
document.querySelectorAll('[data-controller~="stimeo--color-picker"]').forEach((picker) => {
  const sliders = picker.querySelectorAll('[role="slider"]');

  const positionThumbs = () => {
    sliders.forEach((slider) => {
      const now = Number(slider.getAttribute('aria-valuenow'));
      const max = Number(slider.getAttribute('aria-valuemax')) || 1;
      const min = Number(slider.getAttribute('aria-valuemin')) || 0;
      const fraction = max > min ? (now - min) / (max - min) : 0;
      slider.style.setProperty('--stimeo-demo-pos', `${fraction * 100}%`);
    });
  };

  picker.addEventListener('stimeo--color-picker:change', positionThumbs);
  positionThumbs();
});