import { visit } from 'unist-util-visit';

/**
 * rehype 插件：将段落等文本节点拆分为逐词 <span>，并添加淡入动画 class。
 * 仅在流式渲染阶段使用，避免已渲染文字重复动画。
 */
export function rehypeSplitWordsIntoSpans() {
  return (tree) => {
    visit(tree, 'element', (node) => {
      if (
        ['p', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'li', 'strong'].includes(node.tagName) &&
        node.children
      ) {
        const newChildren = [];
        node.children.forEach((child) => {
          if (child.type === 'text') {
            try {
              // 使用 Intl.Segmenter 精准拆分中英文及标点
              const segmenter = new Intl.Segmenter('zh', { granularity: 'word' });
              const segments = segmenter.segment(child.value);
              Array.from(segments)
                .map((seg) => seg.segment)
                .filter(Boolean)
                .forEach((word) => {
                  newChildren.push({
                    type: 'element',
                    tagName: 'span',
                    properties: {
                      className: ['animate-fade-in'],
                    },
                    children: [{ type: 'text', value: word }],
                  });
                });
            } catch (_) {
              // Fallback：如果浏览器不支持 Segmenter，直接输出原文本
              newChildren.push(child);
            }
          } else {
            newChildren.push(child);
          }
        });
        node.children = newChildren;
      }
    });
  };
}