function esc(s: string) {
  return s.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/"/g, '&quot;')
}

export type RssItem = {
  title: string
  url: string
  description?: string
  publishDate: Date
}

export function buildRss(opts: {
  title: string
  description: string
  siteUrl: string
  items: RssItem[]
}) {
  const items = opts.items
    .map(
      (i) => `
    <item>
      <title>${esc(i.title)}</title>
      <link>${esc(opts.siteUrl + i.url)}</link>
      <guid>${esc(opts.siteUrl + i.url)}</guid>
      <pubDate>${i.publishDate.toUTCString()}</pubDate>
      ${i.description ? `<description>${esc(i.description)}</description>` : ''}
    </item>`,
    )
    .join('')
  return `<?xml version="1.0" encoding="UTF-8"?>
<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
  <channel>
    <title>${esc(opts.title)}</title>
    <link>${esc(opts.siteUrl)}</link>
    <description>${esc(opts.description)}</description>
    <atom:link href="${esc(opts.siteUrl)}/rss.xml" rel="self" type="application/rss+xml" />${items}
  </channel>
</rss>`
}