From 5e0a11f6f45d50140c46d706478de53d5231353b Mon Sep 17 00:00:00 2001
From: Peter Stuifzand <peter@stuifzand.eu>
Date: Wed, 1 Jul 2020 22:36:25 +0200
Subject: [PATCH] Add <mark> element ==test==

---
 markdown.go      |  15 ++----
 markdown/mark.go | 138 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 142 insertions(+), 11 deletions(-)
 create mode 100644 markdown/mark.go

diff --git a/markdown.go b/markdown.go
index 5e681fd..d50ede5 100644
--- a/markdown.go
+++ b/markdown.go
@@ -3,21 +3,12 @@ package main
 import (
 	"bytes"
 
-	"gitlab.com/golang-commonmark/markdown"
-
 	"github.com/yuin/goldmark"
 	"github.com/yuin/goldmark/extension"
 	"github.com/yuin/goldmark/renderer/html"
-)
 
-func renderMarkdown(pageText string) string {
-	md := markdown.New(
-		markdown.HTML(true),
-		markdown.XHTMLOutput(true),
-	)
-	pageText = md.RenderToString([]byte(pageText))
-	return pageText
-}
+	"p83.nl/go/wiki/markdown"
+)
 
 func renderMarkdown2(pageText string) string {
 	md := goldmark.New(
@@ -28,6 +19,8 @@ func renderMarkdown2(pageText string) string {
 		),
 	)
 
+	markdown.Mark.Extend(md)
+
 	var buf bytes.Buffer
 	if err := md.Convert([]byte(pageText), &buf); err != nil {
 		panic(err)
diff --git a/markdown/mark.go b/markdown/mark.go
new file mode 100644
index 0000000..ae333b1
--- /dev/null
+++ b/markdown/mark.go
@@ -0,0 +1,138 @@
+package markdown
+
+import (
+	"github.com/yuin/goldmark"
+	gast "github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/renderer"
+	"github.com/yuin/goldmark/renderer/html"
+	"github.com/yuin/goldmark/text"
+	"github.com/yuin/goldmark/util"
+)
+
+// A Strikethrough struct represents a strikethrough of GFM text.
+type AstMark struct {
+	gast.BaseInline
+}
+
+// Dump implements Node.Dump.
+func (n *AstMark) Dump(source []byte, level int) {
+	gast.DumpHelper(n, source, level, nil, nil)
+}
+
+// KindStrikethrough is a NodeKind of the AstMark node.
+var KindMark = gast.NewNodeKind("AstMark")
+
+// Kind implements Node.Kind.
+func (n *AstMark) Kind() gast.NodeKind {
+	return KindMark
+}
+
+// NewStrikethrough returns a new AstMark node.
+func NewAstMark() *AstMark {
+	return &AstMark{}
+}
+
+type markDelimiterProcessor struct {
+}
+
+func (p *markDelimiterProcessor) IsDelimiter(b byte) bool {
+	return b == '='
+}
+
+func (p *markDelimiterProcessor) CanOpenCloser(opener, closer *parser.Delimiter) bool {
+	return opener.Char == closer.Char
+}
+
+func (p *markDelimiterProcessor) OnMatch(consumes int) gast.Node {
+	return NewAstMark()
+}
+
+var defaultMarkDelimiterProcessor = &markDelimiterProcessor{}
+
+type markParser struct {
+}
+
+var defaultMarkParser = &markParser{}
+
+// NewMarkParser return a new InlineParser that parses
+// strikethrough expressions.
+func NewMarkParser() parser.InlineParser {
+	return defaultMarkParser
+}
+
+func (s *markParser) Trigger() []byte {
+	return []byte{'='}
+}
+
+func (s *markParser) Parse(parent gast.Node, block text.Reader, pc parser.Context) gast.Node {
+	before := block.PrecendingCharacter()
+	line, segment := block.PeekLine()
+	node := parser.ScanDelimiter(line, before, 2, defaultMarkDelimiterProcessor)
+	if node == nil {
+		return nil
+	}
+	node.Segment = segment.WithStop(segment.Start + node.OriginalLength)
+	block.Advance(node.OriginalLength)
+	pc.PushDelimiter(node)
+	return node
+}
+
+func (s *markParser) CloseBlock(parent gast.Node, pc parser.Context) {
+	// nothing to do
+}
+
+// MarkHTMLRenderer is a renderer.NodeRenderer implementation that
+// renders Mark nodes.
+type MarkHTMLRenderer struct {
+	html.Config
+}
+
+// NewMarkHTMLRenderer returns a new MarkHTMLRenderer.
+func NewMarkHTMLRenderer(opts ...html.Option) renderer.NodeRenderer {
+	r := &MarkHTMLRenderer{
+		Config: html.NewConfig(),
+	}
+	for _, opt := range opts {
+		opt.SetHTMLOption(&r.Config)
+	}
+	return r
+}
+
+// RegisterFuncs implements renderer.NodeRenderer.RegisterFuncs.
+func (r *MarkHTMLRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
+	reg.Register(KindMark, r.renderMark)
+}
+
+// MarkAttributeFilter defines attribute names which dd elements can have.
+var MarkAttributeFilter = html.GlobalAttributeFilter
+
+func (r *MarkHTMLRenderer) renderMark(w util.BufWriter, source []byte, n gast.Node, entering bool) (gast.WalkStatus, error) {
+	if entering {
+		if n.Attributes() != nil {
+			_, _ = w.WriteString("<mark")
+			html.RenderAttributes(w, n, MarkAttributeFilter)
+			_ = w.WriteByte('>')
+		} else {
+			_, _ = w.WriteString("<mark>")
+		}
+	} else {
+		_, _ = w.WriteString("</mark>")
+	}
+	return gast.WalkContinue, nil
+}
+
+type mark struct {
+}
+
+// Mark is an extension that allow you to use strikethrough expression like '==text==' .
+var Mark = &mark{}
+
+func (e *mark) Extend(m goldmark.Markdown) {
+	m.Parser().AddOptions(parser.WithInlineParsers(
+		util.Prioritized(NewMarkParser(), 500),
+	))
+	m.Renderer().AddOptions(renderer.WithNodeRenderers(
+		util.Prioritized(NewMarkHTMLRenderer(), 500),
+	))
+}