generate rss channel as xml str

lib/rss.typ

@@ -0,0 +1,81 @@
+#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),)
+  )
+}