labsite: Add tooling for Next button

Add markdown tooling for Next button generation from

	[Next]

A `<details>...</details>` HTMLBlock generated from Markdown also stops when a
`[Next]` button is found (in addition to thematic break and heading as end
marker).

As we were developing this we uncovered a bug around newlines inside code blocks
after conversion to HTMLBlock used again as MD. I've snuck in a fix and test
for that too.

build-tools/labsite-gen/main.go

@@ -14,7 +14,12 @@ import (
 	"rsc.io/markdown"
 )
 
-const marker = "[>]"
+const (
+	detailsMarker    = "[>]"
+	nextButtonMarker = "[Next]"
+)
+
+var nextButton = newNextButton()
 
 func main() {
 	if len(os.Args) != 3 {
@@ -34,6 +39,7 @@ func run(mdFile, htmlfFile string) error {
 		return err
 	}
 	doc := parse(string(md))
+	replaceNextButton(doc)
 	doc.Blocks = collapse(doc.Blocks)
 	html := markdown.ToHTML(doc)
 
@@ -45,6 +51,29 @@ func parse(md string) *markdown.Document {
 	return p.Parse(md)
 }
 
+func replaceNextButton(doc *markdown.Document) {
+	for i, block := range doc.Blocks {
+		if isNextButton(block) {
+			doc.Blocks[i] = nextButton
+		}
+	}
+}
+
+func isNextButton(block markdown.Block) bool {
+	paragraph, ok := block.(*markdown.Paragraph)
+	if !ok {
+		return false
+	}
+	if len(paragraph.Text.Inline) != 1 {
+		return false
+	}
+	plain, ok := paragraph.Text.Inline[0].(*markdown.Plain)
+	if !ok {
+		return false
+	}
+	return plain.Text == nextButtonMarker
+}
+
 func collapse(blocks []markdown.Block) []markdown.Block {
 	var result []markdown.Block
 	for idx := 0; idx < len(blocks); {
@@ -75,19 +104,22 @@ func isCollapsible(block markdown.Block) bool {
 		return false
 	}
 	plain, ok := heading.Text.Inline[0].(*markdown.Plain)
-	return ok && strings.HasPrefix(plain.Text, marker)
+	return ok && strings.HasPrefix(plain.Text, detailsMarker)
 }
 
 func deleteCollapseMarker(heading *markdown.Heading) {
 	// assumes isCollapsible returned true
 	plain := heading.Text.Inline[0].(*markdown.Plain)
-	s := strings.TrimPrefix(plain.Text, marker)
+	s := strings.TrimPrefix(plain.Text, detailsMarker)
 	s = strings.TrimLeftFunc(s, unicode.IsSpace)
 	plain.Text = s
 }
 
 func findEndIdx(level, start int, blocks []markdown.Block) int {
 	for i := start; i < len(blocks); i++ {
+		if blocks[i] == nextButton {
+			return i
+		}
 		if _, ok := blocks[i].(*markdown.ThematicBreak); ok {
 			return i
 		}
@@ -110,8 +142,15 @@ func toDetailsHTML(heading *markdown.Heading, blocks []markdown.Block) *markdown
 		buf.WriteString(markdown.ToHTML(block))
 	}
 	buf.WriteString("</details>")
-	doc := parse(buf.String())
-	return doc.Blocks[0].(*markdown.HTMLBlock)
+	htmlBlock := &markdown.HTMLBlock{
+		Text: strings.Split(buf.String(), "\n"),
+	}
+	return htmlBlock
+}
+
+func newNextButton() *markdown.Paragraph {
+	doc := parse(`<button class="next-btn">Next</button>`)
+	return doc.Blocks[0].(*markdown.Paragraph)
 }
 
 func isThematicBreak(blocks []markdown.Block, idx int) bool {

build-tools/labsite-gen/main_test.go

@@ -63,6 +63,26 @@ anybody here?`,
 <summary>goodbye</summary>
 </details>
 </details>
+`[1:],
+	}, {
+		name: "codeblocks",
+		in: `
+# [>] hallo
+
+` + "```evy" + `
+print 1
+
+print 2
+` + "```" + `
+`,
+		want: `
+<details>
+<summary>hallo</summary>
+<pre><code class="language-evy">print 1
+
+print 2
+</code></pre>
+</details>
 `[1:],
 	},
 }
@@ -78,3 +98,61 @@ func TestCollapse(t *testing.T) {
 		})
 	}
 }
+
+var nextButtonTests = []struct {
+	name     string
+	in       string
+	wantMD   string
+	wantHTML string
+}{
+	{
+		name:     "no marker",
+		in:       "hallo",
+		wantMD:   "hallo\n",
+		wantHTML: "<p>hallo</p>\n",
+	},
+	{
+		name:     "single button",
+		in:       `[Next]`,
+		wantMD:   `<button class="next-btn">Next</button>` + "\n",
+		wantHTML: `<p><button class="next-btn">Next</button></p>` + "\n",
+	},
+	{
+		name: "multiple buttons",
+		in: `# Heading
+[Next]
+
+paragraph
+
+[Next]`,
+		wantMD: `
+# Heading
+
+<button class="next-btn">Next</button>
+
+paragraph
+
+<button class="next-btn">Next</button>
+`[1:],
+		wantHTML: `
+<h1>Heading</h1>
+<p><button class="next-btn">Next</button></p>
+<p>paragraph</p>
+<p><button class="next-btn">Next</button></p>
+`[1:],
+	},
+}
+
+func TestReplaceNextButton(t *testing.T) {
+	for _, tt := range nextButtonTests {
+		t.Run(tt.name, func(t *testing.T) {
+			p := markdown.Parser{}
+			doc := p.Parse(tt.in)
+			replaceNextButton(doc)
+			gotMD := markdown.Format(doc)
+			assert.Equal(t, tt.wantMD, gotMD)
+			gotHTML := markdown.ToHTML(doc)
+			assert.Equal(t, tt.wantHTML, gotHTML)
+		})
+	}
+}