export function calculateTotalPages(
  totalItems: number,
  pageSize: number
): number {
  return Math.ceil(totalItems / pageSize);
}

export function getPaginationItems(
  totalPages: number,
  currentPage: number
): (number | string)[] {
  if (totalPages <= 7) {
    return Array.from({ length: totalPages }, (_, i) => i + 1);
  }

  const pages: (number | string)[] = [1];
  if (currentPage <= 4) {
    pages.push(2, 3, 4, 5, '…');
  } else if (currentPage >= totalPages - 3) {
    pages.push(
      '…',
      totalPages - 4,
      totalPages - 3,
      totalPages - 2,
      totalPages - 1
    );
  } else {
    pages.push('…', currentPage - 1, currentPage, currentPage + 1, '…');
  }
  pages.push(totalPages);
  return pages;
}

export function getHiddenPages(
  totalPages: number,
  items: (number | string)[],
  currentPage: number,
  position: 'left' | 'right'
): number[] {
  if (totalPages <= 7) return [];

  const all = Array.from({ length: totalPages }, (_, i) => i + 1);
  const visible = items.filter(x => typeof x === 'number') as number[];
  const hidden = all.filter(p => !visible.includes(p));

  if (position === 'left') {
    const firstAfterEllipsis = visible[1] as number;
    return hidden.filter(p => p < firstAfterEllipsis);
  } else {
    const lastBeforeEllipsis = visible[visible.length - 2] as number;
    return hidden.filter(p => p > lastBeforeEllipsis);
  }
}

export function getRangeText(
  totalItems: number,
  pageSize: number,
  currentPage: number
): string {
  const start = (currentPage - 1) * pageSize + 1;
  const end = Math.min(currentPage * pageSize, totalItems);
  return `Showing ${start}–${end} of ${totalItems}`;
}