Atom feed support (#58)

cmd/mercury/main.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/kgaughan/mercury/internal"
+	"github.com/kgaughan/mercury/internal/atom"
 	"github.com/kgaughan/mercury/internal/feed"
 	"github.com/kgaughan/mercury/internal/flags"
 	"github.com/kgaughan/mercury/internal/manifest"
@@ -83,6 +84,10 @@ func main() {
 			log.Fatal(err)
 		}
 
+		if err := writeFeed(entries, config); err != nil {
+			log.Fatal(err)
+		}
+
 		if err := writeOPML(manifest, path.Join(config.Output, "opml.xml")); err != nil {
 			log.Fatal(err)
 		}
@@ -166,6 +171,52 @@ func writePages(entries []*feed.Entry, feeds []*gofeed.Feed, config internal.Con
 	return nil
 }
 
+func writeFeed(entries []*feed.Entry, config internal.Config) error {
+	feed := atom.Feed{
+		Title:   config.Name,
+		ID:      config.FeedID,
+		Updated: atom.Time(*entries[0].Updated()),
+		Links: []atom.Link{{
+			Rel:  "self",
+			Href: config.URL + "feed.atom",
+		}},
+	}
+
+	for _, entry := range entries {
+		summary := &atom.Text{
+			Type: "html",
+			Body: string(entry.Summary()),
+		}
+		if summary.Body == "" {
+			summary = nil
+		}
+		atomEntry := &atom.Entry{
+			Title: entry.Title(),
+			ID:    entry.ID(),
+			Links: []atom.Link{{
+				Rel:  "alternate",
+				Href: string(entry.Link()),
+			}},
+			Published: atom.Time(*entry.Published()),
+			Updated:   atom.Time(*entry.Updated()),
+			Author: &atom.Person{
+				Name: entry.Author(),
+			},
+			Summary: summary,
+			Content: &atom.Text{
+				Type: "html",
+				Body: string(entry.Content()),
+			},
+		}
+		feed.Entries = append(feed.Entries, atomEntry)
+	}
+
+	if err := utils.MarshalToFile(path.Join(config.Output, "atom.xml"), feed); err != nil {
+		return fmt.Errorf("could not create Atom feed: %w", err)
+	}
+	return nil
+}
+
 func writeOPML(manifest *manifest.Manifest, path string) error {
 	opml := opml.New(manifest.Len())
 	for url, item := range *manifest {

docs/configuration.md

@@ -8,6 +8,7 @@ The top-level configuration fields are:
 | url | string | The base URL of your planet | "" |
 | owner | string | Your name | "" |
 | email | string | Your email | "" |
+| feed_id | string | Unique ID to use for the Atom feed | "" |
 | cache | string | The path, relative to _mercury.toml_ of the feed cache | "./cache" |
 | timeout | duration | How long to wait when fetching a feed | - |
 | theme | string | The path, relative to _mercury.toml_ of the theme to use | "./theme" |
@@ -17,6 +18,8 @@ The top-level configuration fields are:
 
 A _duration_ is a sequence of numbers followed by a unit, with 's' being 'second', 'm' being 'minute', and 'h' being 'hour'. Thus '5m30' would mean five minutes and thirty seconds.
 
+The feed ID is a URI identifying the feed. I would recommend using a [tag URI](https://en.wikipedia.org/wiki/Tag_URI_scheme), or a [UUID](https://en.wikipedia.org/wiki/Universally_unique_identifier) [URN](https://en.wikipedia.org/wiki/Uniform_Resource_Name). In the latter case, use a UUID generator such as `uuidgen` to generate a UUID, prefix it with `urn:uuid:`, and use the result as the value of `feed_id`.
+
 Each feed is introduced with `[[feed]]`, and can contain the following fields:
 
 | Name | Type | Description |

internal/atom/atom.go

@@ -0,0 +1,54 @@
+package atom
+
+import (
+	"encoding/xml"
+	"time"
+)
+
+type Feed struct {
+	XMLName xml.Name `xml:"http://www.w3.org/2005/Atom feed"`
+	Title   string   `xml:"title"`
+	ID      string   `xml:"id"`
+	Links   []Link   `xml:"link"`
+	Updated TimeStr  `xml:"updated"`
+	Author  *Person  `xml:"author"`
+	Entries []*Entry `xml:"entry"`
+}
+
+type Entry struct {
+	Title     string  `xml:"title"`
+	ID        string  `xml:"id"`
+	Links     []Link  `xml:"link"`
+	Published TimeStr `xml:"published"`
+	Updated   TimeStr `xml:"updated"`
+	Author    *Person `xml:"author"`
+	Summary   *Text   `xml:"summary,omitempty"`
+	Content   *Text   `xml:"content,omitempty"`
+}
+
+type Link struct {
+	Rel      string `xml:"rel,attr,omitempty"`
+	Href     string `xml:"href,attr"`
+	Type     string `xml:"type,attr,omitempty"`
+	HrefLang string `xml:"hreflang,attr,omitempty"`
+	Title    string `xml:"title,attr,omitempty"`
+	Length   uint   `xml:"length,attr,omitempty"`
+}
+
+type Person struct {
+	Name     string `xml:"name"`
+	URI      string `xml:"uri,omitempty"`
+	Email    string `xml:"email,omitempty"`
+	InnerXML string `xml:",innerxml"`
+}
+
+type Text struct {
+	Type string `xml:"type,attr"`
+	Body string `xml:",chardata"`
+}
+
+type TimeStr string
+
+func Time(t time.Time) TimeStr {
+	return TimeStr(t.Format("2006-01-02T15:04:05-07:00"))
+}

internal/config.go

@@ -15,6 +15,7 @@ type Config struct {
 	URL          string          `toml:"url"`
 	Owner        string          `toml:"owner"`
 	Email        string          `toml:"email"`
+	FeedID       string          `toml:"feed_id"`
 	Cache        string          `toml:"cache"`
 	Timeout      utils.Duration  `toml:"timeout"`
 	Theme        string          `toml:"theme"`

internal/feed/entry.go

@@ -101,3 +101,7 @@ func (e Entry) Updated() *time.Time {
 func (e Entry) Categories() []string {
 	return e.entry.Categories
 }
+
+func (e Entry) ID() string {
+	return e.entry.GUID
+}

mercury.toml

@@ -1,5 +1,6 @@
 name = "My Planet!"
 url = "http://localhost/"
+feed_id = "uri:urn:5c71947a-107d-4a3d-b635-2bac0cbcd8ba"
 owner = "Chidi Anagonye"
 email = "[email protected]"
 cache = "./cache"

theme/index.html

@@ -6,6 +6,7 @@
 		<meta name="generator" content="{{.Generator}}">
 		<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/normalize/8.0.1/normalize.min.css" integrity="sha384-9Z9AuAj0Xi0z7WFOSgjjow8EnNY9wPNp925TVLlAyWhvZPsf5Ks23Ex0mxIrWJzJ" crossorigin="anonymous">
 		<link rel="stylesheet" href="static/style.css" type="text/css">
+		<link rel="alternate" type="application/atom+xml" href="atom.xml" title="Atom feed">
 		<link rel="outline" type="text/x-opml" href="opml.xml" title="OPML">
 		<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
 	</head>