/**
 * Maps a berth's mooring-letter prefix (A, B, C…) to a subtle visual
 * accent. Pontoons cluster physically - A row is one dock, B another
 * - so the berth grid reads at a glance when each pontoon's rows
 * share a colour cue. Earlier iteration tinted the entire row
 * background; that proved visually noisy. This version keeps rows
 * white and surfaces the colour as a coloured left border, plus a
 * matching dot the column factory uses inside the Mooring # cell.
 *
 * Cycle wraps at the 8th letter; ports with more pontoons get
 * repeats (fine in practice - they don't sit adjacent on the page).
 */
const BORDER_CYCLE = [
  'border-l-4 border-l-rose-400',
  'border-l-4 border-l-amber-400',
  'border-l-4 border-l-emerald-400',
  'border-l-4 border-l-sky-400',
  'border-l-4 border-l-violet-400',
  'border-l-4 border-l-orange-400',
  'border-l-4 border-l-teal-400',
  'border-l-4 border-l-fuchsia-400',
] as const;

const DOT_CYCLE = [
  'bg-rose-400',
  'bg-amber-400',
  'bg-emerald-400',
  'bg-sky-400',
  'bg-violet-400',
  'bg-orange-400',
  'bg-teal-400',
  'bg-fuchsia-400',
] as const;

function indexFor(mooringNumber: string | null | undefined): number | null {
  if (!mooringNumber) return null;
  const letter = mooringNumber.charAt(0).toUpperCase();
  if (letter < 'A' || letter > 'Z') return null;
  return (letter.charCodeAt(0) - 'A'.charCodeAt(0)) % BORDER_CYCLE.length;
}

export function mooringLetterTone(mooringNumber: string | null | undefined): string | undefined {
  const i = indexFor(mooringNumber);
  return i === null ? undefined : BORDER_CYCLE[i];
}

export function mooringLetterDot(mooringNumber: string | null | undefined): string | undefined {
  const i = indexFor(mooringNumber);
  return i === null ? undefined : DOT_CYCLE[i];
}
