import { h, renderList } from '@ui-arch/frame';
import type { PaginationProps } from './types.js';

/*** 页码序列：≤7 页全展开；否则保留首尾与当前页 ±1 窗口，缺口折叠为省略号（null 占位） ***/
function pageSequence(page: number, totalPages: number): (number | null)[] {
  if (totalPages <= 7) return Array.from({ length: totalPages }, (_, i) => i + 1);
  const marks = [1, 2, page - 1, page, page + 1, totalPages - 1, totalPages].filter((p) => p >= 1 && p <= totalPages);
  const seq: (number | null)[] = [];
  let prev = 0;
  for (const p of [...new Set(marks)].sort((a, b) => a - b)) {
    if (p - prev > 1) seq.push(null); // 缺口 → 省略号
    seq.push(p);
    prev = p;
  }
  return seq;
}

/*** 独立分页器：受控组件，page 为双向绑定信号；页码过多折叠省略号，首末页禁用翻页，原生 button 保证键盘可达 ***/
export function pagination(props: PaginationProps): HTMLElement {
  const totalPages = Math.max(1, Math.ceil(props.total / props.pageSize)); // 总页数
  const go = (p: number) => {
    const next = Math.min(totalPages, Math.max(1, p)); // 钳制到有效页码范围
    props.page(next);
    props.onChange?.(next);
  };

  const nav = h('nav', { class: 'ua-pagination', 'aria-label': '分页' });
  renderList(nav, () => {
    const page = Math.min(totalPages, Math.max(1, props.page()));
    const items: HTMLElement[] = [h('button', { class: 'ua-page-btn', disabled: page <= 1, 'aria-label': '上一页', onClick: () => go(page - 1) }, '‹')];
    for (const it of pageSequence(page, totalPages)) {
      items.push(
        it == null
          ? h('span', { class: 'ua-page-gap', 'aria-hidden': 'true' }, '…')
          : h('button', { class: `ua-page-btn${it === page ? ' ua-active' : ''}`, disabled: it === page, 'aria-current': it === page ? 'page' : null, 'aria-label': `第 ${it} 页`, onClick: () => go(it) }, String(it)),
      );
    }
    items.push(h('button', { class: 'ua-page-btn', disabled: page >= totalPages, 'aria-label': '下一页', onClick: () => go(page + 1) }, '›'));
    return items;
  });
  return nav;
}