/** 视频卡片批量选择状态（任务 105）：不变量优先的纯 Set 操作，无框架依赖。 */

/** 空选择集。 */
export function clearVideoSelection(): Set<string> {
  return new Set<string>()
}

function validKey(key: string): boolean {
  return typeof key === 'string' && key.length > 0
}

/** 切换单卡选择(有则移除、无则加入)。 */
export function videoSelectionToggle(selection: Set<string>, key: string): Set<string> {
  const next = new Set(selection)
  if (!validKey(key)) return next
  if (next.has(key)) next.delete(key)
  else next.add(key)
  return next
}

/** 批量加入(幂等)。 */
export function videoSelectionAdd(selection: Set<string>, keys: readonly string[]): Set<string> {
  const next = new Set(selection)
  for (const key of keys) if (validKey(key)) next.add(key)
  return next
}

/** 批量移除(缺失键无操作)。 */
export function videoSelectionRemove(selection: Set<string>, keys: readonly string[]): Set<string> {
  const next = new Set(selection)
  for (const key of keys) next.delete(key)
  return next
}

export function countVideoSelection(selection: Set<string>): number {
  return selection.size
}

/** 是否全部卡被选中(空卡列表视作未全选)。 */
export function allCardsSelected(selection: Set<string>, keys: readonly string[]): boolean {
  return keys.length > 0 && keys.every((key) => selection.has(key))
}

/** 是否部分卡被选中(部分但非全部)。 */
export function partialCardsSelected(selection: Set<string>, keys: readonly string[]): boolean {
  const selectedCount = keys.filter((key) => selection.has(key)).length
  return selectedCount > 0 && selectedCount < keys.length
}