// 通用列表分页器:mono 总数 + 页码窗口 + 每页条数 + 跳页输入。
// 父组件持有 page state;纯前端切片或服务端分页都适用(onChange 回页码)。
// 新增能力全部可选 —— 旧调用方只传 page/total/pageSize/onChange 时退化为原只读分页器:
//   onPageSizeChange  传则「每页 N 条」变成可点击循环按钮(默认循环 12/24/48/96)
//   pageSizeOptions   自定义每页条数候选
//   sticky            传则分页器吸底浮动
//   alwaysShow        单页也渲染(admin 列表用:让「共 N 条 · 每页 10 条」可见,否则数据少时像没接分页)
// 默认 total <= pageSize 且不可改每页条数时不渲染(单页无需分页器)。

import { useState } from "react";

// 页码窗口:超过 7 页折叠成 1 … cur-1 cur cur+1 … last
export function pageWindow(current: number, total: number): Array<number | "ellipsis"> {
  if (total <= 7) return Array.from({ length: total }, (_, i) => i + 1);
  const items: Array<number | "ellipsis"> = [1];
  const start = Math.max(2, current - 1);
  const end = Math.min(total - 1, current + 1);
  if (start > 2) items.push("ellipsis");
  for (let p = start; p <= end; p++) items.push(p);
  if (end < total - 1) items.push("ellipsis");
  items.push(total);
  return items;
}

export function Pager({ page, total, pageSize, onChange, onPageSizeChange, pageSizeOptions = [12, 24, 48, 96], sticky = false, alwaysShow = false }: {
  page: number;
  total: number;
  pageSize: number;
  onChange: (page: number) => void;
  onPageSizeChange?: (size: number) => void;
  pageSizeOptions?: number[];
  sticky?: boolean;
  alwaysShow?: boolean;
}) {
  const totalPages = Math.max(1, Math.ceil(total / pageSize));
  const cur = Math.min(Math.max(1, page), totalPages);
  const [jump, setJump] = useState("");
  // 单页且不可改每页条数 → 不渲染;可改条数或 alwaysShow 时仍渲染
  if (total <= pageSize && !onPageSizeChange && !alwaysShow) return null;

  function cycleSize() {
    if (!onPageSizeChange) return;
    const idx = pageSizeOptions.indexOf(pageSize);
    onPageSizeChange(pageSizeOptions[(idx + 1) % pageSizeOptions.length]);
  }
  function commitJump() {
    const n = Number.parseInt(jump, 10);
    if (Number.isFinite(n)) onChange(Math.min(Math.max(1, n), totalPages));
    setJump("");
  }

  return (
    <div className={`list-pager${sticky ? " sticky" : ""}`}>
      <span className="total">共 {total} 条 · 第 {cur} / {totalPages} 页</span>
      <div className="pages">
        <button type="button" disabled={cur === 1} onClick={() => onChange(cur - 1)} aria-label="上一页">‹</button>
        {pageWindow(cur, totalPages).map((p, i) => (
          p === "ellipsis"
            ? <span key={`e${i}`} className="ellipsis">…</span>
            : <button type="button" key={p} className={p === cur ? "active" : ""} onClick={() => onChange(p)}>{p}</button>
        ))}
        <button type="button" disabled={cur === totalPages} onClick={() => onChange(cur + 1)} aria-label="下一页">›</button>
      </div>
      {totalPages > 7 && (
        <span className="jump">
          跳至
          <input
            type="number"
            min={1}
            max={totalPages}
            value={jump}
            placeholder={String(cur)}
            onChange={(event) => setJump(event.target.value)}
            onKeyDown={(event) => { if (event.key === "Enter") commitJump(); }}
            onBlur={() => { if (jump) commitJump(); }}
            aria-label="跳至页码"
          />
          页
        </span>
      )}
      {onPageSizeChange
        ? <button type="button" className="page-size size-cycle" onClick={cycleSize} title="点击切换每页条数">每页 {pageSize} 条</button>
        : <span className="page-size">每页 {pageSize} 条</span>}
    </div>
  );
}