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

let seq = 0; // 实例序号：给弹层列表一个稳定 id，供 aria-controls 关联

/*** 自动补全：输入即过滤候选项，↑↓ 高亮 / Enter 选中 / Esc 收起，value 信号双向绑定 ***/ 
export function autoComplete(props: AutoCompleteProps): HTMLElement {
  // —— 状态集中声明 ——
  const value: Signal<string> = props.value ?? signal(''); // 输入值
  const open = signal(false);      // 弹层开合
  const query = signal('');        // 当前过滤关键字（与 value 同步，独立信号便于受控写入）
  const active = signal(-1);       // 键盘高亮下标，-1 表示无高亮
  const place = signal<'top' | 'bottom'>('bottom'); // 实际方位
  let releaseEsc: (() => void) | null = null; // Esc 栈注销函数
  const max = props.maxItems ?? 8;

  /*** 按关键字取候选：函数式入参交给调用方计算（可远程联想），结果截断到 maxItems ***/
  const candidates = (): AutoCompleteOption[] => {
    const all = typeof props.options === 'function' ? props.options(query()) : props.options;
    const q = query().trim().toLowerCase();
    const hit = q ? all.filter((o) => o.value.toLowerCase().includes(q)) : all; // 包含匹配，大小写不敏感
    return hit.slice(0, max);
  };

  const input = h('input', {
    type: 'text',
    class: 'ua-autocomplete-input',
    placeholder: props.placeholder ?? '',
    'aria-label': props.placeholder ?? '自动补全',
    role: 'combobox',
    'aria-expanded': () => String(open()),
    'aria-autocomplete': 'list',
    disabled: props.disabled,
    value: () => value(), // 外部写入信号时回填输入框
    oninput: (e: Event) => {
      const v = (e.target as HTMLInputElement).value;
      value(v);
      query(v);
      active(-1);
      open(v.trim().length > 0); // 空串收起，避免开屏就弹
      props.onInput?.(v);
    },
  }) as HTMLInputElement;

  const list = h('ul', { class: 'ua-autocomplete-list', role: 'listbox', id: `ua-ac-${(seq += 1)}` }) as HTMLElement;
  input.setAttribute('aria-controls', list.id);
  const pop = h('div', { class: () => `ua-autocomplete-pop${open() ? ' ua-open' : ''}${place() === 'top' ? ' is-flip' : ''}` }, list) as HTMLElement;
  const root = h('div', { class: 'ua-autocomplete' }, input, pop) as HTMLElement;

  /*** 选中候选：写值 + 收起 + 回调，焦点回到输入框便于继续输入 ***/
  const pick = (opt: AutoCompleteOption): void => {
    value(opt.value);
    query(opt.value);
    open(false);
    active(-1);
    props.onSelect?.(opt);
    input.focus();
  };

  /*** 重绘候选行：高亮项由 active 决定，空结果渲染提示行 ***/
  const render = (): void => {
    const opts = candidates();
    if (!opts.length) {
      list.replaceChildren(h('li', { class: 'ua-autocomplete-empty' }, props.emptyText ?? '无匹配项'));
      input.removeAttribute('aria-activedescendant');
      return;
    }
    const rows = opts.map((opt, i) => {
      const row = h(
        'li',
        {
          class: () => `ua-autocomplete-opt${active() === i ? ' is-active' : ''}`,
          role: 'option',
          id: `${list.id}-${i}`,
          'aria-selected': String(active() === i),
          onmousedown: (e: Event) => { e.preventDefault(); pick(opt); }, // 阻止默认：保住输入框焦点，blur 后仍能选中
        },
        h('span', { class: 'ua-autocomplete-value' }, opt.value),
        opt.hint ? h('span', { class: 'ua-autocomplete-hint' }, opt.hint) : null,
      );
      return row;
    });
    list.replaceChildren(...rows);
    const cur = rows[active()];
    if (cur) input.setAttribute('aria-activedescendant', cur.id); // 读屏跟随高亮
    else input.removeAttribute('aria-activedescendant');
  };

  root.addEventListener('keydown', (e: KeyboardEvent) => {
    const opts = candidates();
    if (e.key === 'ArrowDown' || e.key === 'ArrowUp') {
      e.preventDefault(); // 阻止光标跳行
      if (!open() && opts.length) { open(true); active(0); return; } // 未展开：先展开并高亮首项
      const dir = e.key === 'ArrowDown' ? 1 : -1;
      active((active() + dir + opts.length) % opts.length); // 环形移动
      return;
    }
    if (e.key === 'Enter' && open() && active() >= 0) { e.preventDefault(); pick(opts[active()]); return; } // 有高亮才回车选中
    if (e.key === 'Tab') { open(false); return; } // 失焦前收起，避免残留浮层
  });

  bindOutside(root, open, () => open(false)); // 点外部收起：仅展开期间挂监听，收起即摘
  effect(render); // 依赖 query / active / options，任一变化即重绘
  effect(() => {
    if (open()) releaseEsc ??= pushOverlay(() => { open(false); input.focus(); }); // 入栈逐层关闭
    else { releaseEsc?.(); releaseEsc = null; }
  });
  let releaseShift: (() => void) | null = null; // 展开期间的位移跟随释放函数（滚动 / 缩放重算翻转）
effect(() => {
    if (!open()) { // 收起即摘监听：弹层不在，重算方位没有意义
      releaseShift?.();
      releaseShift = null;
      return;
    }
    place(flip(input, pop, 'bottom')); // 打开先算一次：空间不足自动翻转
    releaseShift ??= trackShift(() => place(flip(input, pop, 'bottom'))); // 展开期间跟着滚动重算：视口空间会变
  }); // 空间不足自动翻转
  return root;
}