import type { Plugin } from 'vite';

/**
 * Vite 插件：资源预加载优化
 * 自动添加 Link 标签预加载关键资源
 */
export default function preloadPlugin(): Plugin {
  return {
    name: 'vite-plugin-preload-optimization',
    apply: 'build',
    transformIndexHtml(html, context) {
      // 只在生产环境添加预加载
      if (process.env.NODE_ENV === 'development') {
        return html;
      }

      const bundle = context.bundle || {};
      const preloadLinks: string[] = [];

      // 收集关键资源
      const criticalChunks = ['vue-vendor', 'element-plus', 'pinia'];
      const criticalAssets: string[] = [];

      Object.entries(bundle).forEach(([fileName, chunk]) => {
        if (chunk.type === 'chunk' && criticalChunks.some(name => fileName.includes(name))) {
          criticalAssets.push(`/${fileName}`);
        }
      });

      // 生成预加载标签
      criticalAssets.forEach(href => {
        if (href.endsWith('.js')) {
          preloadLinks.push(`<link rel="modulepreload" href="${href}" crossorigin>`);
        } else if (href.endsWith('.css')) {
          preloadLinks.push(`<link rel="preload" href="${href}" as="style">`);
        }
      });

      // 将预加载标签插入到 </head> 之前
      if (preloadLinks.length > 0) {
        return html.replace('</head>', `${preloadLinks.join('\n  ')}\n</head>`);
      }

      return html;
    },
  };
}