From 84aff405b134337ad335453f339f46bd86e7bf27 Mon Sep 17 00:00:00 2001
From: Kumar Damani <me@kumardamani.net>
Date: Mon, 3 Aug 2026 13:23:49 -0400
Subject: added atom feed

---
 feed.typ          | 63 +++++++++++++++++++++++++++++++++++++++++++++++++------
 global/common.typ |  3 ++-
 main.typ          |  3 ++-
 3 files changed, 61 insertions(+), 8 deletions(-)

diff --git a/feed.typ b/feed.typ
index 75639e0..3a5fd21 100644
--- a/feed.typ
+++ b/feed.typ
@@ -1,5 +1,6 @@
-// RSS 2.0 feed for the blog posts, emitted as feed.xml by main.typ.
-// Items are built from the metadata in site-info.pages (newest first).
+// RSS 2.0 and Atom feeds for the blog posts, emitted as feed.xml and
+// atom.xml by main.typ. Entries are built from the metadata in
+// site-info.pages (newest first).
 
 #import "/global/common.typ": baseurl
 
@@ -13,16 +14,25 @@
     )
 }
 
-#let feed-xml(site-info) = {
+// ISO date ("2026-07-28") to RFC 3339 ("2026-07-28T00:00:00Z").
+#let rfc3339(iso) = iso + "T00:00:00Z"
+
+#let _entries(site-info, item-fn) = {
     let pages = site-info.pages
     let ids = pages.keys().filter(k => k.starts-with("post/"))
 
-    let items = ()
+    let entries = ()
     for id in ids {
         let p = pages.at(id)
         let title = if "long-title" in p { p.long-title } else { p.title }
         let url = baseurl + "/" + id + ".html"
+        entries.push(item-fn(title, url, p))
+    }
+    entries
+}
 
+#let feed-xml(site-info) = {
+    let items = _entries(site-info, (title, url, p) => {
         let lines = (
             "  <item>",
             "    <title>" + xml-escape(title) + "</title>",
@@ -36,8 +46,8 @@
             lines.push("    <description>" + xml-escape(p.description) + "</description>")
         }
         lines.push("  </item>")
-        items.push(lines.join("\n"))
-    }
+        lines.join("\n")
+    })
 
     (
         "<?xml version=\"1.0\" encoding=\"UTF-8\"?>",
@@ -52,3 +62,44 @@
         "",
     ).join("\n")
 }
+
+// Atom (RFC 4287) feed, emitted as atom.xml by main.typ.
+#let atom-xml(site-info) = {
+    let entries = _entries(site-info, (title, url, p) => {
+        let lines = (
+            "  <entry>",
+            "    <title>" + xml-escape(title) + "</title>",
+            "    <link href=\"" + url + "\"/>",
+            "    <id>" + url + "</id>",
+        )
+        if "date" in p {
+            lines.push("    <updated>" + rfc3339(p.date) + "</updated>")
+        }
+        if "description" in p {
+            lines.push("    <summary>" + xml-escape(p.description) + "</summary>")
+        }
+        lines.push("  </entry>")
+        lines.join("\n")
+    })
+
+    // newest post first, so its date is the feed's last-update time
+    let updated = rfc3339(site-info.pages.at(
+        site-info.pages.keys().filter(k => k.starts-with("post/")).first()
+    ).date)
+
+    (
+        "<?xml version=\"1.0\" encoding=\"UTF-8\"?>",
+        "<feed xmlns=\"http://www.w3.org/2005/Atom\">",
+        "  <title>" + xml-escape(site-info.title) + "</title>",
+        "  <link href=\"" + baseurl + "/\"/>",
+        "  <link rel=\"self\" href=\"" + baseurl + "/atom.xml\"/>",
+        "  <id>" + baseurl + "/</id>",
+        "  <updated>" + updated + "</updated>",
+        "  <author>",
+        "    <name>Kumar</name>",
+        "  </author>",
+        entries.join("\n"),
+        "</feed>",
+        "",
+    ).join("\n")
+}
diff --git a/global/common.typ b/global/common.typ
index d1a0aaa..269fc62 100644
--- a/global/common.typ
+++ b/global/common.typ
@@ -185,6 +185,7 @@
                 html.elem("link", attrs: (rel: "preload", href: base + "extlink.svg", "as": "image"))
                 html.link(rel: "stylesheet", href: base + "main.css")
                 html.link(rel: "alternate", type: "application/rss+xml", title: site + " RSS", href: base + "feed.xml")
+                html.link(rel: "alternate", type: "application/atom+xml", title: site + " Atom", href: base + "atom.xml")
 
                 for ss in stylesheets {
                     html.link(rel: "stylesheet", href: base + ss)
@@ -231,7 +232,7 @@
                 html.footer({
                     html.span(class: "updated")[\[Updated: #ci.date.\]]
                     html.span(class: "logs")[
-                        \[For nerds: #extlink(srcurl)[site source], #extlink(ci.link)[logs], #link(base + "feed.xml")[rss]\]
+                        \[For nerds: #extlink(srcurl)[site source], #extlink(ci.link)[logs], #link(base + "feed.xml")[rss], #link(base + "atom.xml")[atom]\]
                     ]
                 })
             })
diff --git a/main.typ b/main.typ
index e74b903..8eea0e2 100644
--- a/main.typ
+++ b/main.typ
@@ -4,7 +4,7 @@
 
 #import "/global/common.typ": *
 #import "/site.typ": site-info
-#import "/feed.typ": feed-xml
+#import "/feed.typ": feed-xml, atom-xml
 
 #import "/index.typ" as index-page
 #import "/software.typ" as software-page
@@ -76,6 +76,7 @@
 #asset("favicon.ico", read("/global/favicon.ico", encoding: none))
 #asset("favicon.svg", read("/global/favicon.svg", encoding: none))
 #asset("feed.xml", bytes(feed-xml(site-info)))
+#asset("atom.xml", bytes(atom-xml(site-info)))
 
 // image assets collected from pages via the img/fig helpers
 #context {
-- 
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