import type { OutputBundle, OutputChunk } from 'rollup'
import type { Plugin, ResolvedConfig } from 'vite'

type StyleChunk = OutputChunk & { viteMetadata?: { importedCss: Set<string> } }

function staticAssets(bundle: OutputBundle, entry: OutputChunk): Set<string> {
  const assets = new Set<string>()
  const visit = (chunk: StyleChunk) => {
    if (assets.has(chunk.fileName)) return
    assets.add(chunk.fileName)
    for (const css of chunk.viteMetadata?.importedCss ?? []) assets.add(css)
    for (const file of chunk.imports) {
      const dependency = bundle[file]
      if (dependency?.type === 'chunk') visit(dependency)
    }
  }
  visit(entry)
  return assets
}

// Download route resources without evaluating the module or applying its CSS.
export function loginRoutePreload(): Plugin {
  let config: ResolvedConfig
  return {
    name: 'login-route-preload',
    apply: 'build',
    configResolved(resolved) { config = resolved },
    transformIndexHtml: {
      order: 'post',
      handler(_html, context) {
        if (context.path !== '/index.html' || !context.bundle) return
        const bundle = context.bundle
        const chunks = Object.values(bundle).filter((item): item is OutputChunk => item.type === 'chunk')
        const main = chunks.find(chunk => chunk.facadeModuleId === context.filename)
        const login = chunks.find(chunk => chunk.facadeModuleId?.replaceAll('\\', '/').endsWith('/src/views/auth/Login.vue'))
        if (!main || !login) throw new Error('Login route preload could not resolve the main and login chunks')
        const shared = staticAssets(bundle, main)
        const files = [...staticAssets(bundle, login)].filter(file => !shared.has(file))
        const json = (value: unknown) => JSON.stringify(value).replaceAll('<', '\\u003c')
        return [{
          tag: 'script',
          attrs: { 'data-login-route-preload': '' },
          injectTo: 'head-prepend',
          children: `(function(){try{
var base=${json(config.base)},path=location.pathname;
if(base==='./'||base==='')return;
var prefix=new URL(base,location.href).pathname;
if(path.indexOf(prefix)!==0)return;
path=path.slice(prefix.length);
if(path!=='login'&&path!=='login/'&&path!=='register'&&path!=='register/')return;
${json(files)}.forEach(function(file){
var link=document.createElement('link'),css=file.endsWith('.css');
if(!css&&(!link.relList||!link.relList.supports('modulepreload')))return;
link.rel=css?'preload':'modulepreload';
if(css)link.as='style';
link.crossOrigin='';link.href=base+file;
link.setAttribute('data-login-route-preload','');
document.head.appendChild(link);
});
}catch(_){}})();`,
        }]
      },
    },
  }
}