Establish NODE.DC design system baseline

packages/ui-core/src/accent.ts

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+export type RgbTuple = readonly [number, number, number];
+
+export interface AccentVariables {
+  "--nodedc-accent-rgb": string;
+  "--nodedc-on-accent-rgb": string;
+}
+
+function clampChannel(value: number): number {
+  return Math.max(0, Math.min(255, Math.round(value)));
+}
+
+function linearChannel(channel: number): number {
+  const normalized = clampChannel(channel) / 255;
+  return normalized <= 0.04045
+    ? normalized / 12.92
+    : ((normalized + 0.055) / 1.055) ** 2.4;
+}
+
+export function relativeLuminance(rgb: RgbTuple): number {
+  const [red, green, blue] = rgb.map(linearChannel) as [number, number, number];
+  return red * 0.2126 + green * 0.7152 + blue * 0.0722;
+}
+
+export function readableTextRgb(rgb: RgbTuple): RgbTuple {
+  return relativeLuminance(rgb) > 0.46 ? [11, 17, 23] : [247, 248, 244];
+}
+
+export function rgbTuple(value: RgbTuple): string {
+  return value.map(clampChannel).join(" ");
+}
+
+export function createAccentVariables(accent: RgbTuple): AccentVariables {
+  return {
+    "--nodedc-accent-rgb": rgbTuple(accent),
+    "--nodedc-on-accent-rgb": rgbTuple(readableTextRgb(accent)),
+  };
+}
+

packages/ui-core/src/floating.ts

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+export type FloatingPlacement = "bottom-start" | "bottom-end" | "top-start" | "top-end";
+
+export interface RectLike {
+  top: number;
+  right: number;
+  bottom: number;
+  left: number;
+  width: number;
+  height: number;
+}
+
+export interface FloatingPositionOptions {
+  anchor: RectLike;
+  surfaceWidth: number;
+  surfaceHeight: number;
+  placement?: FloatingPlacement;
+  offset?: number;
+  viewportWidth?: number;
+  viewportHeight?: number;
+  viewportPadding?: number;
+}
+
+export interface FloatingPosition {
+  top: number;
+  left: number;
+  maxHeight: number;
+  resolvedPlacement: FloatingPlacement;
+}
+
+export function computeFloatingPosition({
+  anchor,
+  surfaceWidth,
+  surfaceHeight,
+  placement = "bottom-start",
+  offset = 8,
+  viewportWidth = typeof window === "undefined" ? 1920 : window.innerWidth,
+  viewportHeight = typeof window === "undefined" ? 1080 : window.innerHeight,
+  viewportPadding = 8,
+}: FloatingPositionOptions): FloatingPosition {
+  const roomBelow = viewportHeight - anchor.bottom - offset - viewportPadding;
+  const roomAbove = anchor.top - offset - viewportPadding;
+  const requestedTop = placement.startsWith("top");
+  const shouldFlip = requestedTop
+    ? surfaceHeight > roomAbove && roomBelow > roomAbove
+    : surfaceHeight > roomBelow && roomAbove > roomBelow;
+  const resolvedPlacement = shouldFlip
+    ? (`${requestedTop ? "bottom" : "top"}-${placement.endsWith("end") ? "end" : "start"}` as FloatingPlacement)
+    : placement;
+
+  const alignedLeft = resolvedPlacement.endsWith("end")
+    ? anchor.right - surfaceWidth
+    : anchor.left;
+  const left = Math.min(
+    Math.max(viewportPadding, alignedLeft),
+    Math.max(viewportPadding, viewportWidth - surfaceWidth - viewportPadding),
+  );
+
+  const availableHeight = resolvedPlacement.startsWith("top") ? roomAbove : roomBelow;
+  const maxHeight = Math.max(96, availableHeight);
+  const visibleHeight = Math.min(surfaceHeight, maxHeight);
+  const top = resolvedPlacement.startsWith("top")
+    ? Math.max(viewportPadding, anchor.top - offset - visibleHeight)
+    : Math.min(anchor.bottom + offset, viewportHeight - visibleHeight - viewportPadding);
+
+  return { top, left, maxHeight, resolvedPlacement };
+}
+

packages/ui-core/src/index.ts

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+export * from "./accent";
+export * from "./floating";
+export * from "./theme";
+

packages/ui-core/src/theme.ts

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+import { createAccentVariables, type RgbTuple } from "./accent";
+
+export type NodedcTheme = "dark" | "light";
+
+export interface ApplyThemeOptions {
+  theme?: NodedcTheme;
+  accent?: RgbTuple;
+}
+
+export function applyNodedcTheme(
+  target: HTMLElement,
+  { theme = "dark", accent }: ApplyThemeOptions = {},
+): void {
+  target.dataset.nodedcTheme = theme;
+  target.dataset.nodedcUi = "true";
+
+  if (!accent) return;
+  const variables = createAccentVariables(accent);
+  Object.entries(variables).forEach(([property, value]) => {
+    target.style.setProperty(property, value);
+  });
+}
+
+export function clearNodedcAccent(target: HTMLElement): void {
+  target.style.removeProperty("--nodedc-accent-rgb");
+  target.style.removeProperty("--nodedc-on-accent-rgb");
+}
+