2 files changed, 181 insertions, 0 deletions
diff --git a/gemini/gemtext/mdconv/convert.go b/gemini/gemtext/mdconv/convert.go
new file mode 100644
index 0000000..c2f434d
--- /dev/null
+++ b/gemini/gemtext/mdconv/convert.go
@@ -0,0 +1,78 @@
+package mdconv
+
+import (
+	"io"
+	"text/template"
+
+	"tildegit.org/tjp/gus/gemini/gemtext"
+	"tildegit.org/tjp/gus/gemini/gemtext/internal"
+)
+
+// Convert writes markdown to a writer from the provided gemtext document.
+//
+// Templates can be provided to override the output for different line types.
+// The templates supported are:
+//   - "header" is called before any lines and is passed the full Document.
+//   - "footer" is called after the lines and is passed the full Document.
+//   - "textline" is called once per line of text and is passed a gemtext.TextLine.
+//   - "linkline" is called once per link line and is passed a gemtext.LinkLine.
+//   - "preformattedtextlines" is called once for a block of preformatted text and is
+//     passed a slice of gemtext.PreformattedTextLines.
+//   - "heading1line" is called once per h1 line and is passed a gemtext.Heading1Line.
+//   - "heading2line" is called once per h2 line and is passed a gemtext.Heading2Line.
+//   - "heading3line" is called once per h3 line and is passed a gemtext.Heading3Line.
+//   - "listitemlines" is called once for a block of contiguous list item lines and
+//     is passed a slice of gemtext.ListItemLines.
+//   - "quoteline" is passed once per blockquote line and is passed a gemtext.QuoteLine.
+//
+// There exist default implementations of each of these templates, so the "overrides"
+// argument can be nil.
+func Convert(wr io.Writer, doc gemtext.Document, overrides *template.Template) error {
+	if err := internal.ValidateLinks(doc); err != nil {
+		return err
+	}
+
+	tmpl, err := baseTmpl.Clone()
+	if err != nil {
+		return err
+	}
+
+	tmpl, err = internal.AddAllTemplates(tmpl, overrides)
+	if err != nil {
+		return err
+	}
+
+	for _, item := range internal.RenderItems(doc) {
+		if err := tmpl.ExecuteTemplate(wr, item.Template, item.Object); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+var baseTmpl = template.Must(template.New("mdconv").Parse(`
+{{ define "header" }}{{ end }}
+{{ define "textline" }}{{ if ne .String "\n" }}
+{{ . }}{{ end }}{{ end }}
+{{ define "linkline" }}
+=> [{{ if eq .Label "" }}{{ .URL }}{{ else }}{{ .Label }}{{ end }}]({{ .URL }})
+{{ end }}
+{{ define "preformattedtextlines" }}` + "\n```\n" + `{{ range . }}{{ . }}{{ end }}` + "```\n" + `{{ end }}
+{{ define "heading1line" }}
+# {{ .Body }}
+{{ end }}
+{{ define "heading2line" }}
+## {{ .Body }}
+{{ end }}
+{{ define "heading3line" }}
+### {{ .Body }}
+{{ end }}
+{{ define "listitemlines" }}
+{{ range . }}* {{ .Body }}
+{{ end }}{{ end }}
+{{ define "quoteline" }}
+> {{ .Body }}
+{{ end }}
+{{ define "footer" }}{{ end }}
+`))
diff --git a/gemini/gemtext/mdconv/convert_test.go b/gemini/gemtext/mdconv/convert_test.go
new file mode 100644
index 0000000..c8fd53c
--- /dev/null
+++ b/gemini/gemtext/mdconv/convert_test.go
@@ -0,0 +1,103 @@
+package mdconv_test
+
+import (
+	"bytes"
+	"testing"
+	"text/template"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"tildegit.org/tjp/gus/gemini/gemtext"
+	"tildegit.org/tjp/gus/gemini/gemtext/mdconv"
+)
+
+var gmiDoc = `
+# top-level header line
+
+## subtitle
+
+This is some non-blank regular text.
+
+* an
+* unordered
+* list
+
+=> gemini://google.com/ as if
+=> https://google.com/
+
+> this is a quote
+> -tjp
+
+`[1:] + "```pre-formatted code\ndoc := gemtext.Parse(req.Body)\n```ignored closing alt-text\n"
+
+func TestConvert(t *testing.T) {
+	mdDoc := `
+# top-level header line
+
+## subtitle
+
+This is some non-blank regular text.
+
+* an
+* unordered
+* list
+
+=> [as if](gemini://google.com/)
+
+=> [https://google.com/](https://google.com/)
+
+>  this is a quote
+
+>  -tjp
+
+` + "```\ndoc := gemtext.Parse(req.Body)\n```\n"
+
+	doc, err := gemtext.Parse(bytes.NewBufferString(gmiDoc))
+	require.Nil(t, err)
+
+	buf := &bytes.Buffer{}
+	require.Nil(t, mdconv.Convert(buf, doc, nil))
+
+	assert.Equal(t, mdDoc, buf.String())
+}
+
+func TestConvertWithOverrides(t *testing.T) {
+	mdDoc := `
+# h1: top-level header line
+text: 
+## h2: subtitle
+text: 
+text: This is some non-blank regular text.
+text: 
+* li: an
+* li: unordered
+* li: list
+text: 
+=> link: [as if](gemini://google.com/)
+=> link: [https://google.com/](https://google.com/)
+text: 
+> quote:  this is a quote
+> quote:  -tjp
+text: 
+`[1:] + "```\npf: doc := gemtext.Parse(req.Body)\n```\n"
+
+	overrides := template.Must(template.New("overrides").Parse((`
+		{{define "textline"}}text: {{.}}{{end}}
+		{{define "linkline"}}=> link: [{{if eq .Label ""}}{{.URL}}{{else}}{{.Label}}{{end}}]({{.URL}})` + "\n" + `{{end}}
+		{{define "preformattedtextlines"}}` + "```\n" + `{{range . }}pf: {{.}}{{end}}` + "```\n" + `{{end}}
+		{{define "heading1line"}}# h1: {{.Body}}` + "\n" + `{{end}}
+		{{define "heading2line"}}## h2: {{.Body}}` + "\n" + `{{end}}
+		{{define "heading3line"}}### h3: {{.Body}}` + "\n" + `{{end}}
+		{{define "listitemlines"}}{{range .}}* li: {{.Body}}` + "\n" + `{{end}}{{end}}
+		{{define "quoteline"}}> quote: {{.Body}}` + "\n" + `{{end}}
+		`)[1:]))
+
+	doc, err := gemtext.Parse(bytes.NewBufferString(gmiDoc))
+	require.Nil(t, err)
+
+	buf := &bytes.Buffer{}
+	require.Nil(t, mdconv.Convert(buf, doc, overrides))
+
+	assert.Equal(t, mdDoc, buf.String())
+}