From 3e48c02dc66df41ff4183b1e0c4a247e8a1a8831 Mon Sep 17 00:00:00 2001
From: odknt <4185305+odknt@users.noreply.github.com>
Date: Tue, 2 Apr 2019 17:11:41 +0900
Subject: [PATCH] Add task list support

---
 handler.go  |  8 ++++-
 renderer.go | 98 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 105 insertions(+), 1 deletion(-)
 create mode 100644 renderer.go

diff --git a/handler.go b/handler.go
index a71462a..d3ce0d0 100644
--- a/handler.go
+++ b/handler.go
@@ -137,5 +137,11 @@ func markdownFileToHTML(filename string) []byte {
 		panic(err)
 	}
 
-	return blackfriday.Run(bytes, blackfriday.WithExtensions(blackfriday.CommonExtensions))
+	return blackfriday.Run(
+		bytes,
+		blackfriday.WithExtensions(blackfriday.CommonExtensions),
+		blackfriday.WithRenderer(newRenderer(blackfriday.HTMLRendererParameters{
+			Flags: blackfriday.CommonHTMLFlags,
+		})),
+	)
 }
diff --git a/renderer.go b/renderer.go
new file mode 100644
index 0000000..d352665
--- /dev/null
+++ b/renderer.go
@@ -0,0 +1,98 @@
+package main
+
+import (
+	"bytes"
+	"io"
+
+	"github.com/russross/blackfriday/v2"
+)
+
+type renderer struct {
+	*blackfriday.HTMLRenderer
+
+	inTaskList bool
+}
+
+var (
+	checkedTag   = []byte(`<input type="checkbox" checked="" disabled="">`)
+	uncheckedTag = []byte(`<input type="checkbox" disabled="">`)
+
+	taskListTagOpen  = []byte(`<ul class="contains-task-list">`)
+	taskListTagClose = []byte(`</ul>`)
+
+	listItemTagOpen  = []byte(`<li class="task-list-item">`)
+	listItemTagClose = []byte(`</li>`)
+)
+
+func newRenderer(params blackfriday.HTMLRendererParameters) *renderer {
+	return &renderer{
+		HTMLRenderer: blackfriday.NewHTMLRenderer(params),
+	}
+}
+
+func (r *renderer) RenderNode(w io.Writer, node *blackfriday.Node, entering bool) blackfriday.WalkStatus {
+	switch node.Type {
+	case blackfriday.List:
+		if node.ListFlags == blackfriday.ListItemBeginningOfList {
+			if entering {
+				r.inTaskList = r.processTaskList(node)
+				if r.inTaskList {
+					w.Write(taskListTagOpen)
+					return blackfriday.GoToNext
+				}
+			} else {
+				r.inTaskList = false
+			}
+		}
+	case blackfriday.Item:
+		if r.inTaskList {
+			if entering {
+				w.Write(listItemTagOpen)
+			} else {
+				w.Write(listItemTagClose)
+			}
+			return blackfriday.GoToNext
+		}
+	case blackfriday.Text:
+		if r.inTaskList {
+			prefix := r.getTaskListItemPrefix(node)
+			if len(prefix) > 0 {
+				w.Write(prefix)
+				node.Literal = node.Literal[3:]
+			}
+		}
+	}
+	// fallback to blackfriday.Renderer
+	return r.HTMLRenderer.RenderNode(w, node, entering)
+}
+
+func (r *renderer) processTaskList(node *blackfriday.Node) bool {
+	cur := node.FirstChild
+	for cur != nil {
+		child := cur.FirstChild
+		if child.Type != blackfriday.Paragraph {
+			continue
+		}
+
+		child = child.FirstChild
+		if child.Type != blackfriday.Text {
+			continue
+		}
+
+		prefix := r.getTaskListItemPrefix(child)
+		if len(prefix) > 0 {
+			return true
+		}
+		cur = cur.Next
+	}
+	return false
+}
+
+func (r *renderer) getTaskListItemPrefix(node *blackfriday.Node) []byte {
+	if bytes.HasPrefix(node.Literal, []byte("[ ] ")) {
+		return uncheckedTag
+	} else if bytes.HasPrefix(node.Literal, []byte("[x] ")) {
+		return checkedTag
+	}
+	return []byte{}
+}