feat: add frontmatter extraction

main.go

@@ -9,6 +9,9 @@ import (
 )
 
 var tmpl = `
+---
+title: This is the title
+---
 Hello this is the text:
 {{ sh "hledger bal assets" }}
 `
@@ -22,11 +25,33 @@ func sh(command string) string {
 	return fmt.Sprintf("\n```\n%s\n```\n", string(out))
 }
 
+func parseDocument(doc string) (frontmatter string, body string, err error) {
+	doc = strings.TrimLeft(doc, " \n")
+	sep := "---\n"
+	if !strings.HasPrefix(doc, sep) {
+		err = fmt.Errorf("Invalid document: frontmatter required.\n%s", doc)
+		return
+	}
+	parts := strings.Split(doc, sep)
+	if len(parts) < 3 {
+		err = fmt.Errorf("Invalid document: frontmatter required.\n%s", doc)
+		return
+	}
+	frontmatter = parts[1]
+	body = parts[2]
+	return
+}
+
 func main() {
 	funcMap := template.FuncMap{
 		"sh": sh,
 	}
-	t, err := template.New("foo").Funcs(funcMap).Parse(tmpl)
+	frontmatter, body, err := parseDocument(tmpl)
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("'%s'", frontmatter)
+	t, err := template.New("foo").Funcs(funcMap).Parse(body)
 	if err != nil {
 		panic(err)
 	}