1 files changed, 104 insertions, 0 deletions
diff --git a/internal/generator/atom.go b/internal/generator/atom.go
new file mode 100644
index 0000000..259301c
--- /dev/null
+++ b/internal/generator/atom.go
@@ -0,0 +1,104 @@
+package generator
+
+import (
+	"encoding/xml"
+	"fmt"
+	"os"
+	"path/filepath"
+	"time"
+
+	"codeberg.org/snonux/snonux/internal/config"
+	"codeberg.org/snonux/snonux/internal/post"
+)
+
+// atomFeed is the root element of an Atom 1.0 feed document.
+type atomFeed struct {
+	XMLName xml.Name    `xml:"feed"`
+	XMLNS   string      `xml:"xmlns,attr"`
+	Title   string      `xml:"title"`
+	Link    atomLink    `xml:"link"`
+	Updated string      `xml:"updated"`
+	ID      string      `xml:"id"`
+	Entries []atomEntry `xml:"entry"`
+}
+
+type atomLink struct {
+	Href string `xml:"href,attr"`
+	Rel  string `xml:"rel,attr,omitempty"`
+}
+
+type atomEntry struct {
+	Title   string   `xml:"title"`
+	Link    atomLink `xml:"link"`
+	ID      string   `xml:"id"`
+	Updated string   `xml:"updated"`
+	Content atomContent `xml:"content"`
+}
+
+type atomContent struct {
+	Type  string `xml:"type,attr"`
+	Value string `xml:",chardata"`
+}
+
+// generateAtom writes atom.xml to cfg.OutputDir containing the most recent
+// min(len(posts), config.PostsPerPage) entries.
+func generateAtom(posts []*post.Post, cfg *config.Config) error {
+	limit := config.PostsPerPage
+	if len(posts) < limit {
+		limit = len(posts)
+	}
+
+	recent := posts[:limit]
+	entries := buildAtomEntries(recent, cfg.BaseURL)
+
+	updated := time.Now().UTC().Format(time.RFC3339)
+	if len(recent) > 0 {
+		updated = recent[0].Timestamp.UTC().Format(time.RFC3339)
+	}
+
+	feed := atomFeed{
+		XMLNS:   "http://www.w3.org/2005/Atom",
+		Title:   "snonux.foo",
+		Link:    atomLink{Href: cfg.BaseURL + "/"},
+		Updated: updated,
+		ID:      cfg.BaseURL + "/",
+		Entries: entries,
+	}
+
+	return writeAtomFile(feed, filepath.Join(cfg.OutputDir, "atom.xml"))
+}
+
+// buildAtomEntries converts a slice of posts into Atom entry elements.
+func buildAtomEntries(posts []*post.Post, baseURL string) []atomEntry {
+	entries := make([]atomEntry, 0, len(posts))
+
+	for _, p := range posts {
+		entryURL := fmt.Sprintf("%s/posts/%s/", baseURL, p.ID)
+		entry := atomEntry{
+			Title:   fmt.Sprintf("Post %s", p.ID),
+			Link:    atomLink{Href: entryURL, Rel: "alternate"},
+			ID:      entryURL,
+			Updated: p.Timestamp.UTC().Format(time.RFC3339),
+			Content: atomContent{Type: "html", Value: p.Content},
+		}
+		entries = append(entries, entry)
+	}
+
+	return entries
+}
+
+// writeAtomFile marshals feed to XML and writes it to path with XML declaration.
+func writeAtomFile(feed atomFeed, path string) error {
+	data, err := xml.MarshalIndent(feed, "", "  ")
+	if err != nil {
+		return fmt.Errorf("marshal atom feed: %w", err)
+	}
+
+	content := append([]byte(xml.Header), data...)
+
+	if err := os.WriteFile(path, content, 0o644); err != nil {
+		return fmt.Errorf("write atom.xml: %w", err)
+	}
+
+	return nil
+}