Add Atom feed generation

omicron/ssg/output/__init__.py

@@ -8,6 +8,7 @@ from omicron.ssg.output.directory import Directory
 from omicron.ssg.output.symlink import Symlink
 from omicron.ssg.output.tags import Tags, discover_tags
 from omicron.ssg.output.sitemap import Sitemap
+from omicron.ssg.output.feed import Feed, discover_feeds
 
 __all__ = [
     "Output",
@@ -25,4 +26,6 @@ __all__ = [
     "Tags",
     "discover_tags",
     "Sitemap",
+    "Feed",
+    "discover_feeds",
 ]

omicron/ssg/output/feed.py

@@ -0,0 +1,83 @@
+import logging
+from datetime import date
+from pathlib import Path
+from typing import TYPE_CHECKING, Literal
+from xml.etree.ElementTree import Element, ElementTree, SubElement
+from omicron.ssg.output.output import Output
+from omicron.ssg.output.content import Content
+
+log = logging.getLogger(__name__)
+
+if TYPE_CHECKING:
+    from omicron.ssg.site import Site  # for static checking with mypy
+else:
+    Site = "omicron.ssg.site.Site"  # for runtime checking with beartype
+
+ITEMS_PER_FEED = 20
+
+
+def atom_date(d: date) -> str:
+    return f"{d.isoformat()}T00:00:00Z"
+
+
+class Feed(Output):
+    NAMESPACE = "http://www.w3.org/2005/Atom"
+
+    def __init__(
+        self,
+        site: Site,
+        kind: Literal["root", "section"],
+        items: list[Content],
+        label: str | None,
+    ):
+        super().__init__(site, Feed.build_path(kind, label))
+        self.kind = kind
+        self.label = label
+        self.items = sorted(items, key=lambda c: c.created, reverse=True)[
+            :ITEMS_PER_FEED
+        ]
+
+    @staticmethod
+    def build_path(kind: Literal["root", "section"], label: str | None) -> Path:
+        file = Path("atom.xml")
+        if kind == "root":
+            return file
+        assert label, "label can't be None if kind is not root"
+        return Path(label) / file
+
+    def write(self) -> None:
+        feed_url = f"{self.site.origin}{self.url}"
+        title = f"{self.site.name} — {self.label}" if self.label else self.site.name
+        updated = max(
+            (c.updated or c.created for c in self.items), default=date.today()
+        )
+
+        feed = Element("feed", xmlns=Feed.NAMESPACE)
+        SubElement(feed, "title").text = title
+        SubElement(feed, "id").text = feed_url
+        SubElement(feed, "link", rel="self", href=feed_url)
+        SubElement(feed, "updated").text = atom_date(updated)
+
+        for item in self.items:
+            entry = SubElement(feed, "entry")
+            item_url = f"{self.site.origin}{item.url}"
+            SubElement(entry, "title").text = item.title
+            SubElement(entry, "id").text = item_url
+            SubElement(entry, "link", href=item_url)
+            SubElement(entry, "published").text = atom_date(item.created)
+            SubElement(entry, "updated").text = atom_date(item.updated or item.created)
+            if item.summary:
+                summary = SubElement(entry, "summary", type="html")
+                summary.text = str(item.summary)
+
+        dest = self.site.output_path / self.destination
+        dest.parent.mkdir(parents=True, exist_ok=True)
+        ElementTree(feed).write(dest, encoding="utf-8", xml_declaration=True)
+        log.debug("Wrote %s", dest)
+
+
+def discover_feeds(site: Site) -> list[Feed]:
+    outputs = [Feed(site, "root", site.content, None)]
+    for section, items in site.by_section.items():
+        outputs.append(Feed(site, "section", items, section))
+    return outputs

omicron/ssg/site.py

@@ -16,8 +16,10 @@ from omicron.ssg.output import (
     Tags,
     Memory,
     Sitemap,
+    Feed,
     discover_index,
     discover_tags,
+    discover_feeds,
 )
 from omicron.ssg.markdown import highlight_style
 
@@ -199,8 +201,11 @@ class Site:
             sitemap = Sitemap(self)
             self.add_by_path(sitemap)
             self.other_outputs.append(sitemap)
+            for feed in discover_feeds(self):
+                self.add_by_path(feed)
+                self.other_outputs.append(feed)
         else:
-            log.debug("Skipping sitemap, base_url has no domain name")
+            log.debug("Skipping sitemap and feeds, base_url has no domain name")
         log.info("Discovered %d content items", len(self.content))
 
     def clean(self) -> None: