2 files changed, 156 insertions, 0 deletions
diff --git a/http/handlers/templates/functions/functions.go b/http/handlers/templates/functions/functions.go
new file mode 100644
index 0000000..dd2101c
--- /dev/null
+++ b/http/handlers/templates/functions/functions.go
@@ -0,0 +1,3 @@
+// Package functions makes available extra functions within templates being
+// processed by the `http.handlers.templates` directive.
+package functions
diff --git a/http/handlers/templates/functions/gemtext.go b/http/handlers/templates/functions/gemtext.go
new file mode 100644
index 0000000..5419290
--- /dev/null
+++ b/http/handlers/templates/functions/gemtext.go
@@ -0,0 +1,153 @@
+package functions
+
+import (
+	"bufio"
+	"bytes"
+	"errors"
+	"fmt"
+	"html"
+	"io"
+	"strings"
+	"text/template"
+
+	"github.com/caddyserver/caddy/v2"
+	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
+	"github.com/caddyserver/caddy/v2/caddyconfig/httpcaddyfile"
+	"github.com/caddyserver/caddy/v2/modules/caddyhttp/templates"
+)
+
+func init() {
+	caddy.RegisterModule(Gemtext{})
+	httpcaddyfile.RegisterDirective(
+		"gemtext",
+		func(h httpcaddyfile.Helper) ([]httpcaddyfile.ConfigValue, error) {
+			var f Gemtext
+			err := f.UnmarshalCaddyfile(h.Dispenser)
+			return []httpcaddyfile.ConfigValue{{
+				Class: "template_function", Value: f,
+			}}, err
+		},
+	)
+}
+
+type Gemtext struct{}
+
+var _ templates.CustomFunctions = (*Gemtext)(nil)
+
+func (f *Gemtext) CustomTemplateFunctions() template.FuncMap {
+	return template.FuncMap{
+		"gemtext": f.funcGemtext,
+	}
+}
+
+func (Gemtext) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		ID:  "http.handlers.templates.functions.gemtext",
+		New: func() caddy.Module { return new(Gemtext) },
+	}
+}
+
+func sanitizeText(str string) string {
+	return html.EscapeString(strings.TrimSpace(str))
+}
+
+func (*Gemtext) funcGemtext(input any) (string, error) {
+	var (
+		r         = bufio.NewReader(strings.NewReader(caddy.ToString(input)))
+		w         = new(bytes.Buffer)
+		pft, list bool
+		writeErr  error
+	)
+
+	write := func(fmtStr string, args ...any) {
+		if writeErr != nil {
+			return
+		}
+		fmt.Fprintf(w, fmtStr, args...)
+	}
+
+loop:
+	for {
+		if writeErr != nil {
+			return "", fmt.Errorf("writing line: %w", writeErr)
+		}
+
+		line, err := r.ReadString('\n')
+
+		switch {
+		case errors.Is(err, io.EOF):
+			break loop
+
+		case err != nil:
+			return "", fmt.Errorf("reading next line: %w", err)
+
+		case strings.HasPrefix(line, "```"):
+			if !pft {
+				write("<pre>\n")
+				pft = true
+			} else {
+				write("</pre>\n")
+				pft = false
+			}
+			continue
+
+		case pft:
+			write(line)
+			continue
+
+		case len(strings.TrimSpace(line)) == 0:
+			continue
+		}
+
+		// list case is special, because it requires a prefix and suffix tag
+		if strings.HasPrefix(line, "*") {
+			if !list {
+				write("<ul>\n")
+			}
+			write("<li>%s</li>\n", sanitizeText(line[1:]))
+			list = true
+			continue
+		} else if list {
+			write("</ul>\n")
+			list = false
+		}
+
+		switch {
+		case strings.HasPrefix(line, "=>"):
+			// TODO convert gemini:// links ?
+			var (
+				line   = strings.TrimSpace(line[2:])
+				urlStr = line
+				label  = urlStr
+			)
+			if i := strings.IndexAny(urlStr, " \t"); i > -1 {
+				urlStr, label = urlStr[:i], sanitizeText(urlStr[i:])
+			}
+			write("<p><a href=\"%s\">%s</a></p>\n", urlStr, label)
+
+		case strings.HasPrefix(line, "###"):
+			write("<h3>%s</h3>\n", sanitizeText(line[3:]))
+
+		case strings.HasPrefix(line, "##"):
+			write("<h2>%s</h2>\n", sanitizeText(line[2:]))
+
+		case strings.HasPrefix(line, "#"):
+			write("<h1>%s</h1>\n", sanitizeText(line[1:]))
+
+		case strings.HasPrefix(line, ">"):
+			write("<blockquote>%s</blockquote>\n", sanitizeText(line[1:]))
+
+		default:
+			line = strings.TrimSpace(line)
+			write("<p>%s</p>\n", line)
+		}
+	}
+
+	return w.String(), nil
+}
+
+// UnmarshalCaddyfile implements caddyfile.Unmarshaler.
+func (*Gemtext) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
+	d.Next() // consume directive name
+	return nil
+}