import { effect, h, signal } from '@ui-arch/frame';
import type { Signal } from '@ui-arch/frame';
import { pushOverlay } from './overlay.js';
import { flip } from './position.js';
import type { CascaderOption, CascaderProps } from './types.js';

/*** 沿路径解析节点链：路径失效时在断点截断，避免脏数据把列算错 ***/
function chain(options: CascaderOption[], path: string[]): CascaderOption[] {
  const out: CascaderOption[] = [];
  let level = options;
  for (const v of path) {
    const hit = level.find((o) => o.value === v);
    if (!hit) break;
    out.push(hit);
    level = hit.children ?? [];
  }
  return out;
}

/*** 级联选择：多列联动面板，悬停下钻 / 点击提交，value 信号双向绑定，Esc 与弹层栈共用逐层关闭 ***/
export function cascader(props: CascaderProps): HTMLElement {
  // —— 状态集中声明 ——
  const open = signal(false);                     // 面板开合
  const place = signal<'top' | 'bottom'>('bottom'); // 实际方位：空间不足自动翻转
  const value: Signal<string[]> = props.value ?? signal<string[]>([]); // 已提交路径
  const path = signal<string[]>([]);              // 浏览路径（悬停/下钻都会改，不等于已提交）
  const sep = props.separator ?? ' / ';           // 路径分隔符
  let releaseEsc: (() => void) | null = null;     // Esc 栈注销函数

  const panels = h('div', { class: 'ua-cascader-panels', role: 'menu' }) as HTMLElement; // 多列容器
  const labelText = (): string => chain(props.options, value()).map((o) => o.label).join(sep); // 触发器文案

  /*** 由浏览路径推出各列选项：根列恒在，逐级 append 子级 ***/
  const columns = (): CascaderOption[][] => {
    const out: CascaderOption[][] = [props.options];
    for (let d = 0; d < path().length; d++) {
      const node = out[d].find((o) => o.value === path()[d]);
      if (!node?.children?.length) break; // 断在叶子：后续不再出列
      out.push(node.children);
    }
    return out;
  };

  /*** 提交路径：写信号 + 回调 + 收起并把焦点还给触发器 ***/
  const commit = (p: string[]): void => {
    value(p);
    props.onChange?.([...p]);
    open(false);
    trigger.focus();
  };

  /*** 造一列：当前路径高亮、已提交路径打标、有子级显示下钻箭头 ***/
  const column = (opts: CascaderOption[], depth: number): HTMLElement => {
    const cur = path()[depth];   // 本列浏览中的值
    const done = value()[depth]; // 本列已提交的值
    const rows = opts.map((o) => {
      const hasChild = Boolean(o.children?.length);
      const cls = `ua-cascader-opt${o.value === cur ? ' is-active' : ''}${o.value === done ? ' is-picked' : ''}${o.disabled ? ' is-disabled' : ''}`;
      return h(
        'button',
        {
          type: 'button',
          class: cls,
          role: 'menuitem',
          'aria-haspopup': hasChild ? 'true' : 'false',
          disabled: o.disabled === true, // 禁用项既不可选也不可下钻
          onClick: () => {
            path([...path().slice(0, depth), o.value]); // 点选即把路径截断到本列
            if (!hasChild || props.changeOnSelect) commit([...path().slice(0, depth), o.value]); // 叶子或允许中间层：立即提交
          },
          onmouseenter: () => {
            if (o.disabled || o.value === cur) return; // 卫语句：禁用项与当前项不触发联动
            path([...path().slice(0, depth), o.value]);
          },
        },
        h('span', { class: 'ua-cascader-label' }, o.label),
        hasChild ? h('span', { class: 'ua-cascader-arrow', 'aria-hidden': 'true' }, '›') : null,
      );
    });
    return h('ul', { class: 'ua-cascader-col', role: 'group' }, ...rows) as HTMLElement;
  };

  /*** 重绘所有列：列数随浏览深度增长 ***/
  const render = (): void => {
    const cols = columns();
    panels.replaceChildren(...cols.map((opts, d) => column(opts, d)));
  };

  /*** 把焦点送到某列第 i 项（重建后 DOM 已换，必须等下一帧） ***/
  const focusCol = (depth: number, i = 0): void => {
    requestAnimationFrame(() => {
      const ul = panels.children[depth] as HTMLElement | undefined;
      if (!ul) return; // 卫语句：列不存在
      (ul.children[Math.min(i, ul.children.length - 1)] as HTMLElement | undefined)?.focus();
    });
  };

  // —— 触发器 ——
  const trigger = h(
    'button',
    {
      type: 'button',
      class: 'ua-cascader-trigger',
      'aria-haspopup': 'menu',
      'aria-expanded': () => String(open()),
      disabled: props.disabled,
      onClick: () => { if (!open()) path([...value()]); open(!open()); },
    },
    h('span', { class: () => `ua-cascader-value${value().length ? '' : ' is-empty'}` }, () => labelText() || props.placeholder || '请选择'),
    h('span', { class: 'ua-cascader-caret', 'aria-hidden': 'true' }, '▾'),
  );

  const pop = h('div', { class: () => `ua-cascader-pop${open() ? ' ua-open' : ''}${place() === 'top' ? ' is-flip' : ''}` }, panels);
  const root = h('div', { class: () => `ua-cascader${open() ? ' ua-open' : ''}` }, trigger, pop);

  // 面板键盘导航：↑↓ 同列移动、→ 下钻、← 回退、Enter 提交，Esc 交给弹层栈
  panels.addEventListener('keydown', (e: KeyboardEvent) => {
    const btn = document.activeElement as HTMLElement | null;
    const ul = btn?.parentElement as HTMLElement | null;
    if (!ul?.classList.contains('ua-cascader-col') || !btn) return; // 卫语句：焦点不在选项上
    const siblings = Array.from(ul.children); // 列内项，HTMLCollection 不能直接展开
    const depth = Array.from(panels.children).indexOf(ul); // 当前列序号
    const at = siblings.indexOf(btn);
    if (e.key === 'ArrowDown' || e.key === 'ArrowUp') {
      e.preventDefault();
      const next = siblings[(at + (e.key === 'ArrowDown' ? 1 : -1) + siblings.length) % siblings.length] as HTMLElement;
      next?.focus(); // 列内环形移动
      return;
    }
    if (e.key === 'ArrowRight') { e.preventDefault(); btn.click(); if (open()) focusCol(depth + 1); return; } // 下钻并聚焦新列首项
    if (e.key === 'ArrowLeft') { e.preventDefault(); focusCol(Math.max(depth - 1, 0), at); return; } // 回退到上一列同序项
    if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); btn.click(); } // 与鼠标点击同语义
  });

  document.addEventListener('click', (e) => {
    if (root.contains(e.target as Node)) return; // 卫语句：组件内点击不处理
    open(false); // 点外部收起
  });
  effect(render); // 依赖 open / path / value，任一变化即重绘
  effect(() => {
    if (open()) releaseEsc ??= pushOverlay(() => { open(false); trigger.focus(); }); // 入栈：与弹窗/抽屉共用逐层关闭
    else { releaseEsc?.(); releaseEsc = null; }
  });
  effect(() => { if (open()) place(flip(trigger, pop, 'bottom')); }); // 空间不足自动翻转
  return root;
}