// The order of the articles of a section, as a person proposes another one
// (Yvv, 2026-10-30: « une simple liste clipable »): click an article, then its
// new place — or move it with its arrows. The rules of the vote (who is in the
// order, an order completed at the end) are the server's (ADR 0009).

/** The article `chosen` takes the place of `target`; the others close up. */
export function place(list: string[], chosen: string, target: string): string[] {
  const from = list.indexOf(chosen);
  const to = list.indexOf(target);
  if (from < 0 || to < 0 || from === to) return list;
  const next = list.filter((id) => id !== chosen);
  next.splice(to, 0, chosen);
  return next;
}

/** One place up (-1) or down (1), never beyond the ends. */
export function step(list: string[], id: string, by: -1 | 1): string[] {
  const from = list.indexOf(id);
  const to = from + by;
  if (from < 0 || to < 0 || to >= list.length) return list;
  const target = list[to];
  return target === undefined ? list : place(list, id, target);
}

export function sameOrder(a: string[], b: string[]): boolean {
  return a.length === b.length && a.every((id, i) => b[i] === id);
}

/** The articles whose place changed from `before` to `after`. */
export function moved(before: string[], after: string[]): Set<string> {
  return new Set(after.filter((id, i) => before[i] !== id));
}