import React, { useState } from 'react';
import './Cascader.css';

/* 级联选择器（移动端）— 规格 §44。
   多级联动：点某一级后下一级选项变化；点路径条里的上级可回退（规格 §44.5）。
   级数不写死：路径条按已选深度渲染，面板**只渲染当前一层** —— 375px 宽下并排多列会把
   每列压到 100px 以内，无法阅读（规格 §44.2）。
   路径的当前位置以 data-level 暴露，选中项以 is-selected + aria-selected 双通道表达。
   本端只回传下一段路径（change），确认由宿主决定是否采纳。 */

/* 选项可以是字符串，也可以是 { label, value, disabled, children } 结点（规格 §44.7） */
function nodeOf(option, i) {
  if (option === null || option === undefined) return { label: '', value: String(i) };
  if (typeof option === 'object') {
    return {
      label: String(option.label === undefined ? '' : option.label),
      value: String(option.value === undefined ? i : option.value),
      disabled: !!option.disabled,
      children: Array.isArray(option.children) ? option.children : []
    };
  }
  return { label: String(option), value: String(option) };
}

function normTree(options) {
  return (Array.isArray(options) ? options : []).map(nodeOf);
}

/* 沿 path 走到第 depth 级的选项数组（depth=0 是根） */
function levelList(tree, path, depth) {
  let list = tree;
  for (let i = 0; i < depth; i++) {
    const hit = list.find((n) => n.value === String(path[i]));
    if (!hit || !hit.children.length) return [];
    list = hit.children;
  }
  return list;
}

/* 当前展示层级：末项是叶子时停在它所在层（可改选同级），否则展示下一级 */
function displayDepth(tree, path) {
  let depth = path.length;
  if (depth > 0) {
    const parent = levelList(tree, path, depth - 1);
    const last = parent.find((n) => n.value === String(path[depth - 1]));
    if (last && !last.children.length) depth -= 1;
  }
  return depth;
}

/* 路径条：已选各级的结点（用于渲染可点回的按钮） */
function pathItems(tree, path) {
  const out = [];
  let list = tree;
  for (let i = 0; i < path.length; i++) {
    const hit = list.find((n) => n.value === String(path[i]));
    if (!hit) break;
    out.push(hit);
    list = hit.children;
  }
  return out;
}

const LAYER_LABELS = ['省份', '城市', '区县'];

export default function Cascader({
  mode = 'panel',
  round = false,
  showPath = true,
  open = false,
  closeOnMask = true,
  value = [],
  options = [],
  disabled = false,
  title = '',
  label = '级联选项',
  onChange,
  onConfirm,
  onClose,
  children = null,
}) {
  const tree = normTree(options);
  const path = Array.isArray(value) ? value.map(String) : [];
  /* null = 跟随 value 属性；点选后本地记账，确认前不改宿主的值 */
  const [draft, setDraft] = useState(null);
  const picked = draft || path;

  const depth = displayDepth(tree, picked);
  const list = levelList(tree, picked, depth);
  const pickedValue = picked[depth];
  const items = pathItems(tree, picked);
  const total = items.length;

  const cls =
    'kole-m-cascader' +
    ` kole-m-cascader--${mode === 'popup' ? 'popup' : 'panel'}` +
    (showPath ? '' : ' kole-m-cascader--no-path') +
    (round ? ' kole-m-cascader--round' : '') +
    (open ? ' is-open' : '') +
    (disabled ? ' is-disabled' : '');

  function emitPath(next) {
    setDraft(next);
    if (onChange) onChange(next);
  }

  /* 点选项：截断更深的层级，写入本级选中值（规格 §44.5） */
  function pick(node) {
    if (disabled || node.disabled) return;
    const next = picked.slice(0, depth);
    next[depth] = node.value;
    emitPath(next);
  }

  /* 点路径条上的上级：退回该级，重新展示它的下一级 */
  function back(d) {
    if (disabled) return;
    emitPath(picked.slice(0, d + 1));
  }

  const pathEl = showPath ? (
    <div className="kole-m-cascader__path">
      {items.map((item, i) => {
        const isLast = i === items.length - 1;
        return (
          <React.Fragment key={item.value + i}>
            <button
              className={'kole-m-cascader__path-item' + (isLast ? ' is-current' : '')}
              type="button"
              aria-current={isLast ? 'true' : undefined}
              disabled={isLast}
              onClick={() => back(i)}
            >
              {item.label}
            </button>
            {isLast ? null : (
              <span className="kole-m-cascader__sep" aria-hidden="true">
                ›
              </span>
            )}
          </React.Fragment>
        );
      })}
    </div>
  ) : null;

  const panelEl =
    list.length > 0 ? (
      <ul
        className="kole-m-cascader__panel"
        role="listbox"
        aria-label={label + ' · ' + (LAYER_LABELS[depth] || '第 ' + (depth + 1) + ' 级')}
      >
        {list.map((node, i) => {
          const selected = String(node.value) === String(pickedValue === undefined ? '' : pickedValue);
          const off = disabled || node.disabled;
          const isLeaf = node.children.length === 0;
          return (
            <li
              className={
                'kole-m-cascader__option' + (selected ? ' is-selected' : '') + (off ? ' is-disabled' : '')
              }
              role="option"
              aria-selected={selected ? 'true' : 'false'}
              aria-disabled={off ? 'true' : undefined}
              key={node.value + i}
              onClick={() => pick(node)}
            >
              <span className="kole-m-cascader__label">{node.label}</span>
              {isLeaf ? (
                <span className="kole-m-cascader__check" aria-hidden="true">
                  ✓
                </span>
              ) : (
                <span className="kole-m-cascader__arrow" aria-hidden="true">
                  ›
                </span>
              )}
            </li>
          );
        })}
      </ul>
    ) : (
      <p className="kole-m-cascader__empty">该级暂无可选项</p>
    );

  if (mode === 'popup') {
    return (
      <>
        {children}
        <div
          className={'kole-m-cascader__mask' + (open ? ' is-open' : '')}
          aria-hidden="true"
          onClick={() => {
            if (closeOnMask && onClose) onClose();
          }}
        />
        <div
          className={cls}
          role="dialog"
          aria-modal="true"
          aria-label={title || '选择地区'}
          aria-hidden={open ? undefined : 'true'}
        >
          <div className="kole-m-cascader__header">
            <button
              className="kole-m-cascader__btn"
              type="button"
              onClick={() => {
                if (onClose) onClose();
              }}
            >
              取消
            </button>
            <span className="kole-m-cascader__title">{title || '选择地区'}</span>
            <button
              className="kole-m-cascader__btn kole-m-cascader__btn--confirm"
              type="button"
              onClick={() => {
                if (!disabled && onConfirm) onConfirm(picked);
              }}
            >
              确定
            </button>
          </div>
          {pathEl}
          {panelEl}
        </div>
      </>
    );
  }

  return (
    <div className={cls} role="group" aria-label={label} data-level={depth}>
      {pathEl}
      {panelEl}
      {children}
    </div>
  );
}