gemtext -> atom converter

* add GemsubToAtom converter function
* add Server.Handler method and implementations

fixes #1

2 files changed, 182 insertions, 0 deletions

diff --git a/gemini/gemtext/sub.go b/gemini/gemtext/sub.go
new file mode 100644
index 0000000..a99bed2
--- /dev/null
+++ b/gemini/gemtext/sub.go
@@ -0,0 +1,122 @@
+package gemtext
+
+import (
+	"bytes"
+	"html/template"
+	"net/url"
+	"regexp"
+	"strconv"
+	"strings"
+	"time"
+)
+
+type gemSub struct {
+	ID       template.URL
+	Title    string
+	Subtitle string
+	Updated  string
+
+	Entries []gemSubEntry
+}
+
+type gemSubEntry struct {
+	ID      template.URL
+	Updated string
+	Title   string
+}
+
+var linkElemRE = regexp.MustCompile(`(\d{4})-([0-1]\d)-([0-3]\d)`)
+
+func parseGemSub(doc Document, location *url.URL) *gemSub {
+	sub := &gemSub{ID: template.URL(location.String())}
+	updated := time.Time{}
+
+	for i, line := range doc {
+		switch line.Type() {
+		case LineTypeHeading1:
+			if sub.Title != "" {
+				continue
+			}
+
+			sub.Title = line.(HeadingLine).Body()
+
+			for { // skip any empty lines
+				i += 1
+				if i >= len(doc) || strings.TrimPrefix(doc[i].String(), "\r") != "\n" {
+					break
+				}
+			}
+			if i < len(doc) && doc[i].Type() == LineTypeHeading2 {
+				sub.Subtitle = doc[i].(HeadingLine).Body()
+			}
+		case LineTypeLink:
+			label := line.(LinkLine).Label()
+			if len(label) < 10 {
+				continue
+			}
+			match := linkElemRE.FindStringSubmatch(label[:10])
+			if match == nil {
+				continue
+			}
+
+			year, err := strconv.Atoi(match[1])
+			if err != nil {
+				continue
+			}
+			month, err := strconv.Atoi(match[2])
+			if err != nil || month > 12 {
+				continue
+			}
+			day, err := strconv.Atoi(match[3])
+			if err != nil || day > 31 {
+				continue
+			}
+
+			entryUpdated := time.Date(year, time.Month(month), day, 12, 0, 0, 0, time.UTC)
+			entryTitle := strings.TrimLeft(strings.TrimPrefix(strings.TrimLeft(label[10:], " \t"), "-"), " \t")
+
+			sub.Entries = append(sub.Entries, gemSubEntry{
+				ID:      template.URL(line.(LinkLine).URL()),
+				Updated: entryUpdated.Format(time.RFC3339),
+				Title:   entryTitle,
+			})
+
+			if entryUpdated.After(updated) {
+				updated = entryUpdated
+				sub.Updated = updated.Format(time.RFC3339)
+			}
+		}
+	}
+
+	return sub
+}
+
+func GemsubToAtom(doc Document, location url.URL) string {
+	buf := &bytes.Buffer{}
+	if err := atomTmpl.Execute(buf, parseGemSub(doc, &location)); err != nil {
+		panic(err)
+	}
+	return `<?xml version="1.0" encoding="utf-8"?>` + "\n" + buf.String()
+}
+
+
+
+var atomTmpl = template.Must(template.New("atom").Parse(`
+<feed xmlns="http://www.w3.org/2005/Atom">
+  <id>{{.ID}}</id>
+  <link href="{{.ID}}"/>
+  <title>{{.Title}}</title>
+  {{- if .Subtitle }}
+  <subtitle>{{.Subtitle}}</subtitle>
+  {{- end }}
+  <updated>{{.Updated}}</updated>
+{{- range .Entries }}
+  <entry>
+    <id>{{.ID}}</id>
+    <link rel="alternate" href="{{.ID}}"/>
+    <title>{{.Title}}</title>
+    <updated>{{.Updated}}</updated>
+  </entry>
+{{- end }}
+</feed>
+`[1:]))
diff --git a/gemini/gemtext/sub_test.go b/gemini/gemtext/sub_test.go
new file mode 100644
index 0000000..8bba682
--- /dev/null
+++ b/gemini/gemtext/sub_test.go
@@ -0,0 +1,60 @@
+package gemtext
+
+import (
+	"bytes"
+	"net/url"
+	"testing"
+)
+
+func TestGemsubToAtom(t *testing.T) {
+	tests := []struct {
+		url    string
+		input  string
+		output string
+	}{
+		{
+			url: "gemini://sombodys.site/a/page",
+			input: `
+# This is a gemlog page
+
+
+## with a subtitle after empty lines
+
+=> ./first-post.gmi 2023-08-25 - This is my first post
+`[1:],
+			output: `
+<?xml version="1.0" encoding="utf-8"?>
+<feed xmlns="http://www.w3.org/2005/Atom">
+  <id>gemini://sombodys.site/a/page</id>
+  <link href="gemini://sombodys.site/a/page"/>
+  <title>This is a gemlog page</title>
+  <subtitle>with a subtitle after empty lines</subtitle>
+  <updated>2023-08-25T12:00:00Z</updated>
+  <entry>
+    <id>./first-post.gmi</id>
+    <link rel="alternate" href="./first-post.gmi"/>
+    <title>This is my first post</title>
+    <updated>2023-08-25T12:00:00Z</updated>
+  </entry>
+</feed>
+`[1:],
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.url, func(t *testing.T) {
+			doc, err := Parse(bytes.NewBufferString(test.input))
+			if err != nil {
+				t.Fatal(err)
+			}
+			loc, err := url.Parse(test.url)
+			if err != nil {
+				t.Fatal(err)
+			}
+			xml := GemsubToAtom(doc, *loc)
+			if xml != test.output {
+				t.Fatal("mismatched output")
+			}
+		})
+	}
+}