UI Pro

/**
 * Computes a viewport-relative `{top, left}` (paired with `position: fixed`, matching
 * `getBoundingClientRect`'s coordinate space) for a panel anchored to `trigger` on the
 * `preferred` side. Flips to the opposite side if the preferred side would overflow the viewport
 * and the opposite side fits better; otherwise falls back to `preferred` unfit. Both axes are then
 * clamped into `[gap, viewport - panel - gap]` — cheap insurance on the axis that already fit (a
 * no-op there) and the only thing keeping the *main* axis on-screen when neither placement fit.
 * A panel taller/wider than the viewport can still get clamped to `gap` on both ends and overflow
 * regardless — coordinates alone can't shrink it, so panels also carry their own
 * `max-height`/`overflow-y: auto` (see `.cs-popover`/`.cs-menu`) as the belt-and-braces.
 */
export function computeFloatingPosition(
  trigger: Rect,
  panel: Size,
  viewport: Size,
  preferred: Placement = "bottom",
  gap = 8,
): FloatingPosition {
  const placement = fits(preferred, trigger, panel, viewport, gap)
    ? preferred
    : fits(OPPOSITE[preferred], trigger, panel, viewport, gap)
      ? OPPOSITE[preferred]
      : preferred;

  const { top, left } = place(placement, trigger, panel, gap);

  const clampedLeft = Math.min(
    Math.max(left, gap),
    Math.max(gap, viewport.width - panel.width - gap),
  );
  const clampedTop = Math.min(
    Math.max(top, gap),
    Math.max(gap, viewport.height - panel.height - gap),
  );

  return { top: clampedTop, left: clampedLeft, placement };
}