initial commit

README.md

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+# A Markdown Renderer for the BlackFriday library
+
+## Use case
+
+This renderer enables "Markdown to Markdown" processing.
+
+## Remaining work
+
+* Markdown tables
+* HTML elements
+* Definition lists
+* Fenced code blocks, quotes, and paragraph when part of a list
+
+## License
+
+Licensed under the MIT License

go.mod

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+module github.com/nmasse-itix/blackfriday-markdown-renderer
+
+go 1.14
+
+require (
+	github.com/russross/blackfriday/v2 v2.0.1
+	github.com/shurcooL/sanitized_anchor_name v1.0.0 // indirect
+)

go.sum

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+github.com/russross/blackfriday v1.5.2 h1:HyvC0ARfnZBqnXwABFeSZHpKvJHJJfPz81GNueLj0oo=
+github.com/russross/blackfriday/v2 v2.0.1 h1:lPqVAte+HuHNfhJ/0LC98ESWRz8afy9tM/0RK8m9o+Q=
+github.com/russross/blackfriday/v2 v2.0.1/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
+github.com/shurcooL/sanitized_anchor_name v1.0.0 h1:PdmoCO6wvbs+7yrJyMORt4/BmY5IYyJwS/kOiWx8mHo=
+github.com/shurcooL/sanitized_anchor_name v1.0.0/go.mod h1:1NzhyTcUVG4SuEtjjoZeVRXNmyL/1OwPU0+IJeTBvfc=

main.go

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+package bfmdrenderer
+
+import (
+	"io"
+	"log"
+	"strconv"
+
+	bf "github.com/russross/blackfriday/v2"
+)
+
+// Option defines the functional option type
+type Option func(r *Renderer)
+
+// NewRenderer will return a new renderer with sane defaults
+func NewRenderer(options ...Option) *Renderer {
+	r := &Renderer{}
+	for _, option := range options {
+		option(r)
+	}
+	return r
+}
+
+// Renderer is a custom Blackfriday renderer
+type Renderer struct {
+	paragraphDecoration  []byte
+	nestedListLevel      int
+	nestedListDecoration []byte
+	orderedListCounters  []int
+}
+
+// Taken from the black friday HTML renderer
+func skipParagraphTags(node *bf.Node) bool {
+	parent := node.Parent
+	if parent != nil && parent.Type == bf.BlockQuote {
+		return true
+	}
+
+	grandparent := node.Parent.Parent
+	if grandparent == nil || grandparent.Type != bf.List {
+		return false
+	}
+
+	return grandparent.Type == bf.List && grandparent.Tight
+}
+
+// RenderNode satisfies the Renderer interface
+func (r *Renderer) RenderNode(w io.Writer, node *bf.Node, entering bool) bf.WalkStatus {
+	switch node.Type {
+	case bf.Document:
+		return bf.GoToNext
+	case bf.BlockQuote:
+		if entering {
+			r.paragraphDecoration = append(r.paragraphDecoration, byte('>'), byte(' '))
+		} else {
+			r.paragraphDecoration = r.paragraphDecoration[:len(r.paragraphDecoration)-2]
+		}
+		return bf.GoToNext
+	case bf.List:
+		if entering {
+			r.orderedListCounters = append(r.orderedListCounters, 0)
+			r.nestedListLevel++
+			if r.nestedListLevel > 1 {
+				r.nestedListDecoration = append(r.nestedListDecoration, byte(' '), byte(' '))
+			}
+		} else {
+			if r.nestedListLevel > 1 {
+				r.nestedListDecoration = r.nestedListDecoration[:len(r.nestedListDecoration)-2]
+			} else {
+				w.Write([]byte("\n"))
+			}
+			r.nestedListLevel--
+			r.orderedListCounters = r.orderedListCounters[:len(r.orderedListCounters)-1]
+		}
+
+		return bf.GoToNext
+	case bf.Item:
+		if entering {
+			w.Write(r.nestedListDecoration)
+			if node.Parent.ListFlags&bf.ListTypeOrdered != 0 {
+				r.orderedListCounters[len(r.orderedListCounters)-1]++
+				w.Write([]byte(strconv.Itoa(r.orderedListCounters[len(r.orderedListCounters)-1])))
+				w.Write([]byte{node.ListData.Delimiter})
+				w.Write([]byte(" "))
+			} else if node.Parent.ListFlags&bf.ListTypeTerm != 0 {
+				log.Println("Definition lists not implemented by Renderer")
+			} else {
+				w.Write([]byte{node.ListData.BulletChar})
+				w.Write([]byte(" "))
+			}
+		}
+		return bf.GoToNext
+	case bf.Paragraph:
+		if entering {
+			w.Write(r.paragraphDecoration)
+		} else {
+			w.Write([]byte("\n"))
+			if !skipParagraphTags(node) {
+				w.Write([]byte("\n"))
+			}
+		}
+		return bf.GoToNext
+	case bf.Heading:
+		if entering {
+			for i := 0; i < node.Level; i++ {
+				w.Write([]byte("#"))
+			}
+			w.Write([]byte(" "))
+		} else {
+			w.Write([]byte("\n\n"))
+		}
+		return bf.GoToNext
+	case bf.HorizontalRule:
+		w.Write([]byte("---\n\n"))
+		return bf.GoToNext
+	case bf.Emph:
+		w.Write([]byte("*"))
+		return bf.GoToNext
+	case bf.Strong:
+		w.Write([]byte("**"))
+		return bf.GoToNext
+	case bf.Del:
+		w.Write([]byte("~~"))
+		return bf.GoToNext
+	case bf.Link:
+		if entering {
+			w.Write([]byte("["))
+		} else {
+			w.Write([]byte("]("))
+			w.Write(node.LinkData.Destination)
+			w.Write([]byte(")"))
+		}
+		return bf.GoToNext
+	case bf.Image:
+		if entering {
+			w.Write([]byte("!["))
+		} else {
+			w.Write([]byte("]("))
+			w.Write(node.LinkData.Destination)
+			w.Write([]byte(")"))
+		}
+		return bf.GoToNext
+	case bf.Code:
+		w.Write([]byte("`"))
+		w.Write(node.Literal)
+		w.Write([]byte("`"))
+		return bf.GoToNext
+	case bf.Text:
+		w.Write(node.Literal)
+		return bf.GoToNext
+	case bf.CodeBlock:
+		w.Write([]byte("```"))
+		w.Write(node.CodeBlockData.Info)
+		w.Write([]byte("\n"))
+		w.Write(node.Literal)
+		w.Write([]byte("```\n\n"))
+		return bf.GoToNext
+	case bf.Softbreak:
+		log.Println("Soft breaks not implemented by renderer")
+	case bf.Hardbreak:
+		w.Write([]byte("  \n"))
+		return bf.GoToNext
+	case bf.HTMLBlock:
+		fallthrough
+	case bf.HTMLSpan:
+		log.Println("HTML elements not implemented by renderer")
+	case bf.Table:
+		fallthrough
+	case bf.TableCell:
+		fallthrough
+	case bf.TableHead:
+		fallthrough
+	case bf.TableBody:
+		fallthrough
+	case bf.TableRow:
+		log.Println("Markdown tables not implemented by renderer")
+	default:
+		log.Printf("Unknown BlackFriday Node type '%s'\n", node.Type)
+	}
+
+	return bf.SkipChildren
+}
+
+// RenderHeader satisfies the Renderer interface
+func (r *Renderer) RenderHeader(w io.Writer, ast *bf.Node) {
+	// Nothing required here
+}
+
+// RenderFooter satisfies the Renderer interface
+func (r *Renderer) RenderFooter(w io.Writer, ast *bf.Node) {
+	// Nothing required here
+}

test/reference.md

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+# An h1 header
+
+Paragraphs are separated by a blank line.
+
+2nd paragraph. *Italic*, **bold**, `monospace`. Itemized lists look like:
+
+-	this one
+-	that one
+-	the other one
+
+Nothing to note here.
+
+> Block quotes are written like so.
+>
+> > They can be nested.
+>
+> They can span multiple paragraphs, if you like.
+
+-	Item 1
+-	Item 2
+	-	Item 2a
+		-	Item 2a
+	-	Item 2b
+-	Item 3
+
+Hmm.
+
+1.	Item 1
+2.	Item 2
+	1.	Blah.
+	2.	Blah.
+3.	Item 3
+	-	Item 3a
+	-	Item 3b
+
+Large spacing...
+
+1.	An entire paragraph is written here, and bigger spacing between list items is desired. This is supported too.
+
+2.	Item 2
+
+	1.	Blah.
+
+	2.	Blah.
+
+3.	Item 3
+
+	-	Item 3a
+
+	-	Item 3b
+
+Last paragraph here.
+
+## An h2 header
+
+-	Paragraph right away.
+-	**Big item**: Right away after header.
+
+[Visit GitHub!](www.github.com)
+
+![Hmm](http://example.org/image.png)
+
+![Alt text](/path/to/img.jpg "Optional title") ![Alt text](/path/to/img.jpg "Hello \" 世界")
+
+~~Mistaken text.~~
+
+This (**should** be *fine*).
+
+A \> B.
+
+It's possible to backslash escape \<html\> tags and \`backticks\`. They are treated as text.
+
+1986\. What a great season.
+
+The year was 1986. What a great season.
+
+\*literal asterisks\*.
+
+---
+
+http://example.com
+
+Now a [link](www.github.com) in a paragraph. End with [link_underscore.go](www.github.com).
+
+-	[Link](www.example.com)
+
+### An h3 header
+
+Here's a numbered list:
+
+1.	first item
+2.	second item
+3.	third item
+
+By the way, instead of indenting the block, you can use delimited blocks, if you like:
+
+```
+define foobar() {
+    print "Welcome to flavor country!";
+}
+```
+
+(which makes copying & pasting easier). You can optionally mark the delimited block for Pandoc to syntax highlight it:
+
+```Go
+func main() {
+	println("Hi.")
+}
+```
+
+## Nested Lists
+
+### Codeblock within list
+
+- list1
+
+  ```C
+  if (i == 5)
+    break;
+  ```
+
+### Blockquote within list
+
+- list1
+
+  > This a quote within a list.
+
+### Multi-level nested
+
+- Item 1
+
+  Another paragraph inside this list item is indented just like the previous paragraph.
+
+- Item 2
+
+  - Item 2a
+
+    Things go here.
+
+    > This a quote within a list.
+
+    And they stay here.
+
+  - Item 2b
+
+- Item 3
+
+## Line Breaks
+
+Some text with two trailing spaces for linebreak.  
+More text immediately after.  
+Useful for writing poems.
+
+Done.