/**
 * Per-order color helper.
 *
 * Hashes an order id into one of six curated Tailwind colours so each
 * order group renders with a stable, distinct accent on list pages
 * (Collection Confirm, Invoicing). The same id always picks the same
 * colour across every render and every page.
 *
 * FNV-1a gives an even distribution with no deps. Empty / null ids
 * fall back to the first palette entry so the helper is total.
 */

export type OrderColor = {
  /** Left-edge stripe class, e.g. `border-emerald-500/40`. */
  borderClass: string;
  /** Faint body tint, e.g. `bg-emerald-500/8`. Available for callers
   *  that want a coloured background; not used by the current pages. */
  bgClass: string;
};

export const ORDER_COLOR_PALETTE: ReadonlyArray<OrderColor> = [
  { borderClass: "border-emerald-500/40", bgClass: "bg-emerald-500/8" },
  { borderClass: "border-sky-500/40", bgClass: "bg-sky-500/8" },
  { borderClass: "border-amber-500/40", bgClass: "bg-amber-500/8" },
  { borderClass: "border-rose-500/40", bgClass: "bg-rose-500/8" },
  { borderClass: "border-violet-500/40", bgClass: "bg-violet-500/8" },
  { borderClass: "border-teal-500/40", bgClass: "bg-teal-500/8" },
];

const FNV_OFFSET = 0x811c9dc5;
const FNV_PRIME = 0x01000193;
const PALETTE_SIZE = ORDER_COLOR_PALETTE.length;

export function colorForOrder(orderId: string | undefined | null): OrderColor {
  if (!orderId) return ORDER_COLOR_PALETTE[0];
  let hash = FNV_OFFSET;
  for (let i = 0; i < orderId.length; i++) {
    hash ^= orderId.charCodeAt(i);
    // `>>> 0` keeps the value in the uint32 range so Math.imul
    // doesn't produce a negative result on overflow.
    hash = Math.imul(hash, FNV_PRIME) >>> 0;
  }
  return ORDER_COLOR_PALETTE[hash % PALETTE_SIZE];
}