/**
 * presence-color (TASK-0093) — map a presence palette NAME (the value the
 * server stamps in `user.color`, from the shared `presenceColor(userId)`
 * 20-name palette) to concrete CSS colors the web can render.
 *
 * Decision (recorded, slice 3b): the web has no per-presence-color design
 * tokens yet (the app's `--factory-color-*` tokens cover only the 9 block
 * colors, not the 20 presence names), so each palette name is rendered as a
 * DISTINCT HUE derived from its index in the shared palette
 * (`hue = index * 360/20`). This is deterministic per user (same name →
 * same hue everywhere), keeps the 20-color collision-resistance (20 distinct
 * hues), and hard-codes no hex in the component (the a11y rule: color is
 * never the sole identifier — the name label is mandatory, so hue similarity
 * is harmless). Token-izing to an official design-system palette is a
 * follow-up if the design team ships presence colors.
 *
 * Pure — no DOM, no hex literals (the hsl() is computed at runtime from the
 * palette index, so the Phase-4 "no hardcoded hex in the component" rule
 * holds).
 */
import { PRESENCE_PALETTE } from "@factory/shared/presence";

export interface PresenceColors {
  /** The peer's main color (caret, avatar ring, name-label text). */
  readonly solid: string;
  /** A translucent version (remote selection highlight, ~25 %). */
  readonly soft: string;
  /** A darker version (name-label background — white text on it). */
  readonly labelBg: string;
  /** A light version (avatar background). */
  readonly softBg: string;
}

const STEP = 360 / PRESENCE_PALETTE.length; // 18° per slot

/** The hue (0–360) for a palette name. Unknown names fall back to slot 0. */
export function presenceHue(name: string): number {
  const i = PRESENCE_PALETTE.indexOf(name);
  return (i < 0 ? 0 : i) * STEP;
}

/** Renderable colors for a palette name (see the module decision). */
export function presenceColors(name: string): PresenceColors {
  const h = presenceHue(name);
  return {
    solid: `hsl(${h} 72% 40%)`,
    soft: `hsl(${h} 72% 45% / 0.25)`,
    labelBg: `hsl(${h} 62% 34%)`,
    softBg: `hsl(${h} 60% 88%)`,
  };
}