#import "./summary.typ": summary-sort-key

// TODO DOCUMENT

#let xml-tag(
  name,
  attrs: (),
  children: none,
  body: none,
) = {
  assert(not ((children != none) and (body != none)), message: "children and body cannot be set at the same time")

  ("<" + name 
    + if attrs.len() != 0 { " " } else { "" } 
    + attrs.map(attr => attr.at(0) + "=\"" + attr.at(1) + "\"").join(" ") 
  + if children == none and body == none { "/>" } else if children != none { 
    (
      ">\n  " + children.join("\n").replace("\n", "\n  ") + 
      "\n</" + name + ">"
    )
  } else if body != none {
    ">" + body + "</" + name + ">"
  } else {
    panic("children and body cannot be set at the same time")
  })
}

// We don't care about the hour, but RFC 822 requires it, so use 0 and GMT
#let date-format-rfc822 = "[day padding:zero] [month repr:short] [year repr:full] 00:00:01 +0000"

#let rss(
  title,
  link,
  description,
  rss-url,
  summaries,
  language: "en-us",
  managing-editor: none,
  webmaster: none,
) = {
  let channel-element = (
    xml-tag("title", body: title),
    xml-tag("link", body: link),
    xml-tag("description", body: description),
    xml-tag("language", body: language),
    xml-tag("lastBuildDate", body: datetime.today().display(date-format-rfc822)),
    xml-tag("docs", body: "https://www.rssboard.org/rss-specification"),
    xml-tag("generator", body: "Some random Typst scrypt"),
    xml-tag("atom:link", attrs: (
      ("href", rss-url),
      ("rel", "self"),
      ("type", "application/rss+xml")
    )),
  )
  if managing-editor != none {
    channel-element.push(xml-tag("managingEditor", body: managing-editor))
  }
  if webmaster != none {
    channel-element.push(xml-tag("webMaster", body: webmaster))
  }
  let items = summaries.sorted(
    key: summary-sort-key
  ).map(it => xml-tag(
    "item",
    children: (
      xml-tag("title", body: it.document-args.title),
      xml-tag("link", body: it.template-args.url),
      xml-tag("guid", body: it.template-args.url),
      xml-tag("description", body: it.document-args.description),
      xml-tag("pubDate", body: it.document-args.date.display(date-format-rfc822)),
    ) + it.template-args.tags.map(tag => xml-tag("category", body: tag))
  ))
  xml-tag(
    "rss", 
    attrs: (
      ("xmlns:atom", "http://www.w3.org/2005/Atom"), 
      ("version","2.0")
    ), 
    children: (xml-tag("channel", children: channel-element + items),)
  )
}