Source: inline.go in package github.com/russross/blackfriday/v2

Blackfriday Markdown Processor Available at http://github.com/russross/blackfriday Copyright © 2011 Russ Ross <russ@russross.com>. Distributed under the Simplified BSD License. See README.md for details.

Functions to parse inline elements.


package blackfriday

import (
	"bytes"
	"regexp"
	"strconv"
)

var (
	urlRe    = `((https?|ftp):\/\/|\/)[-A-Za-z0-9+&@#\/%?=~_|!:,.;\(\)]+`
	anchorRe = regexp.MustCompile(`^(<a\shref="` + urlRe + `"(\stitle="[^"<>]+")?\s?>` + urlRe + `<\/a>)`)

https://www.w3.org/TR/html5/syntax.html#character-references highest unicode code point in 17 planes (2^20): 1,114,112d = 7 dec digits or 6 hex digits named entity references can be 2-31 characters with stuff like < at one end and &CounterClockwiseContourIntegral; at the other. There are also sometimes numbers at the end, although this isn't inherent in the specification; there are never numbers anywhere else in current character references, though; see ¾ and &blk12;, etc. https://www.w3.org/TR/html5/syntax.html#named-character-references entity := "&" (named group | number ref) ";" named group := [a-zA-Z]{2,31}[0-9]{0,2} number ref := "#" (dec ref | hex ref) dec ref := [0-9]{1,7} hex ref := ("x" | "X") [0-9a-fA-F]{1,6}

	htmlEntityRe = regexp.MustCompile(`&([a-zA-Z]{2,31}[0-9]{0,2}|#([0-9]{1,7}|[xX][0-9a-fA-F]{1,6}));`)
)

Functions to parse text within a block Each function returns the number of chars taken care of data is the complete block being rendered offset is the number of valid chars before the current cursor

handlers might call us recursively: enforce a maximum depth

	if p.nesting >= p.maxNesting || len(data) == 0 {
		return
	}
	p.nesting++
	beg, end := 0, 0
	for end < len(data) {
		handler := p.inlineCallback[data[end]]
		if handler != nil {

No action from the callback.

				end++

Copy inactive chars into the output.

				currBlock.AppendChild(text(data[beg:end]))
				if node != nil {
					currBlock.AppendChild(node)

Skip past whatever the callback used.

				beg = end + consumed
				end = beg
			}
		} else {
			end++
		}
	}
	if beg < len(data) {
		if data[end-1] == '\n' {
			end--
		}
		currBlock.AppendChild(text(data[beg:end]))
	}
	p.nesting--
}

single and double emphasis parsing

func emphasis(p *Markdown, data []byte, offset int) (int, *Node) {
	data = data[offset:]
	c := data[0]

whitespace cannot follow an opening emphasis; strikethrough only takes two characters '~~'

		if c == '~' || isspace(data[1]) {
			return 0, nil
		}
		ret, node := helperEmphasis(p, data[1:], c)
		if ret == 0 {
			return 0, nil
		}

		return ret + 1, node
	}

	if len(data) > 3 && data[1] == c && data[2] != c {
		if isspace(data[2]) {
			return 0, nil
		}
		ret, node := helperDoubleEmphasis(p, data[2:], c)
		if ret == 0 {
			return 0, nil
		}

		return ret + 2, node
	}

	if len(data) > 4 && data[1] == c && data[2] == c && data[3] != c {
		if c == '~' || isspace(data[3]) {
			return 0, nil
		}
		ret, node := helperTripleEmphasis(p, data, 3, c)
		if ret == 0 {
			return 0, nil
		}

		return ret + 3, node
	}

	return 0, nil
}

func codeSpan(p *Markdown, data []byte, offset int) (int, *Node) {
	data = data[offset:]

	nb := 0

count the number of backticks in the delimiter

	for nb < len(data) && data[nb] == '`' {
		nb++
	}

find the next delimiter

	i, end := 0, 0
	for end = nb; end < len(data) && i < nb; end++ {
		if data[end] == '`' {
			i++
		} else {
			i = 0
		}
	}

no matching delimiter?

	if i < nb && end >= len(data) {
		return 0, nil
	}

trim outside whitespace

	fBegin := nb
	for fBegin < end && data[fBegin] == ' ' {
		fBegin++
	}

	fEnd := end - nb
	for fEnd > fBegin && data[fEnd-1] == ' ' {
		fEnd--
	}

render the code span

	if fBegin != fEnd {
		code := NewNode(Code)
		code.Literal = data[fBegin:fEnd]
		return end, code
	}

	return end, nil
}

newline preceded by two spaces becomes <br>

func maybeLineBreak(p *Markdown, data []byte, offset int) (int, *Node) {
	origOffset := offset
	for offset < len(data) && data[offset] == ' ' {
		offset++
	}

	if offset < len(data) && data[offset] == '\n' {
		if offset-origOffset >= 2 {
			return offset - origOffset + 1, NewNode(Hardbreak)
		}
		return offset - origOffset, nil
	}
	return 0, nil
}

newline without two spaces works when HardLineBreak is enabled

func lineBreak(p *Markdown, data []byte, offset int) (int, *Node) {
	if p.extensions&HardLineBreak != 0 {
		return 1, NewNode(Hardbreak)
	}
	return 0, nil
}

type linkType int

const (
	linkNormal linkType = iota
	linkImg
	linkDeferredFootnote
	linkInlineFootnote
)

func isReferenceStyleLink(data []byte, pos int, t linkType) bool {
	if t == linkDeferredFootnote {
		return false
	}
	return pos < len(data)-1 && data[pos] == '[' && data[pos+1] != '^'
}

func maybeImage(p *Markdown, data []byte, offset int) (int, *Node) {
	if offset < len(data)-1 && data[offset+1] == '[' {
		return link(p, data, offset)
	}
	return 0, nil
}

func maybeInlineFootnote(p *Markdown, data []byte, offset int) (int, *Node) {
	if offset < len(data)-1 && data[offset+1] == '[' {
		return link(p, data, offset)
	}
	return 0, nil
}

'[': parse a link or an image or a footnote

no links allowed inside regular links, footnote, and deferred footnotes

	if p.insideLink && (offset > 0 && data[offset-1] == '[' || len(data)-1 > offset && data[offset+1] == '^') {
		return 0, nil
	}

	var t linkType

special case: ![^text] == deferred footnote (that follows something with an exclamation point)

	case p.extensions&Footnotes != 0 && len(data)-1 > offset && data[offset+1] == '^':

![alt] == image

	case offset >= 0 && data[offset] == '!':
		t = linkImg

^[text] == inline footnote [^refId] == deferred footnote

	case p.extensions&Footnotes != 0:
		if offset >= 0 && data[offset] == '^' {
			t = linkInlineFootnote
			offset++
		} else if len(data)-1 > offset && data[offset+1] == '^' {
			t = linkDeferredFootnote

[text] == regular link

	default:
		t = linkNormal
	}

	data = data[offset:]

	var (
		i                       = 1
		noteID                  int
		title, link, altContent []byte
		textHasNl               = false
	)

	if t == linkDeferredFootnote {
		i++
	}

look for the matching closing bracket

	for level := 1; level > 0 && i < len(data); i++ {
		switch {
		case data[i] == '\n':
			textHasNl = true

		case data[i-1] == '\\':
			continue

		case data[i] == '[':
			level++

		case data[i] == ']':
			level--
			if level <= 0 {
				i-- // compensate for extra i++ in for loop
			}
		}
	}

	if i >= len(data) {
		return 0, nil
	}

	txtE := i
	i++
	var footnoteNode *Node

skip any amount of whitespace or newline (this is much more lax than original markdown syntax)

	for i < len(data) && isspace(data[i]) {
		i++
	}

inline style link

	switch {

skip initial whitespace

		i++

		for i < len(data) && isspace(data[i]) {
			i++
		}

		linkB := i

look for link end: ' " )

	findlinkend:
		for i < len(data) {
			switch {
			case data[i] == '\\':
				i += 2

			case data[i] == ')' || data[i] == '\'' || data[i] == '"':
				break findlinkend

			default:
				i++
			}
		}

		if i >= len(data) {
			return 0, nil
		}
		linkE := i

look for title end if present

		titleB, titleE := 0, 0
		if data[i] == '\'' || data[i] == '"' {
			i++
			titleB = i

		findtitleend:
			for i < len(data) {
				switch {
				case data[i] == '\\':
					i += 2

				case data[i] == ')':
					break findtitleend

				default:
					i++
				}
			}

			if i >= len(data) {
				return 0, nil
			}

skip whitespace after title

			titleE = i - 1
			for titleE > titleB && isspace(data[titleE]) {
				titleE--
			}

check for closing quote presence

			if data[titleE] != '\'' && data[titleE] != '"' {
				titleB, titleE = 0, 0
				linkE = i
			}
		}

remove whitespace at the end of the link

		for linkE > linkB && isspace(data[linkE-1]) {
			linkE--
		}

remove optional angle brackets around the link

		if data[linkB] == '<' {
			linkB++
		}
		if data[linkE-1] == '>' {
			linkE--
		}

build escaped link and title

		if linkE > linkB {
			link = data[linkB:linkE]
		}

		if titleE > titleB {
			title = data[titleB:titleE]
		}

		i++

reference style link

	case isReferenceStyleLink(data, i, t):
		var id []byte
		altContentConsidered := false

look for the id

		i++
		linkB := i
		for i < len(data) && data[i] != ']' {
			i++
		}
		if i >= len(data) {
			return 0, nil
		}
		linkE := i

find the reference

		if linkB == linkE {
			if textHasNl {
				var b bytes.Buffer

				for j := 1; j < txtE; j++ {
					switch {
					case data[j] != '\n':
						b.WriteByte(data[j])
					case data[j-1] != ' ':
						b.WriteByte(' ')
					}
				}

				id = b.Bytes()
			} else {
				id = data[1:txtE]
				altContentConsidered = true
			}
		} else {
			id = data[linkB:linkE]
		}

find the reference with matching id

		lr, ok := p.getRef(string(id))
		if !ok {
			return 0, nil
		}

keep link and title from reference

		link = lr.link
		title = lr.title
		if altContentConsidered {
			altContent = lr.text
		}
		i++

shortcut reference style link or reference or inline footnote

	default:
		var id []byte

craft the id

		if textHasNl {
			var b bytes.Buffer

			for j := 1; j < txtE; j++ {
				switch {
				case data[j] != '\n':
					b.WriteByte(data[j])
				case data[j-1] != ' ':
					b.WriteByte(' ')
				}
			}

			id = b.Bytes()
		} else {
			if t == linkDeferredFootnote {
				id = data[2:txtE] // get rid of the ^
			} else {
				id = data[1:txtE]
			}
		}

		footnoteNode = NewNode(Item)

create a new reference

			noteID = len(p.notes) + 1

			var fragment []byte
			if len(id) > 0 {
				if len(id) < 16 {
					fragment = make([]byte, len(id))
				} else {
					fragment = make([]byte, 16)
				}
				copy(fragment, slugify(id))
			} else {
				fragment = append([]byte("footnote-"), []byte(strconv.Itoa(noteID))...)
			}

			ref := &reference{
				noteID:   noteID,
				hasBlock: false,
				link:     fragment,
				title:    id,
				footnote: footnoteNode,
			}

			p.notes = append(p.notes, ref)

			link = ref.link
			title = ref.title

find the reference with matching id

			lr, ok := p.getRef(string(id))
			if !ok {
				return 0, nil
			}

			if t == linkDeferredFootnote {
				lr.noteID = len(p.notes) + 1
				lr.footnote = footnoteNode
				p.notes = append(p.notes, lr)
			}

keep link and title from reference

if inline footnote, title == footnote contents

			title = lr.title
			noteID = lr.noteID
		}

rewind the whitespace

		i = txtE + 1
	}

	var uLink []byte
	if t == linkNormal || t == linkImg {
		if len(link) > 0 {
			var uLinkBuf bytes.Buffer
			unescapeText(&uLinkBuf, link)
			uLink = uLinkBuf.Bytes()
		}

links need something to click on and somewhere to go

		if len(uLink) == 0 || (t == linkNormal && txtE <= 1) {
			return 0, nil
		}
	}

call the relevant rendering function

	var linkNode *Node
	switch t {
	case linkNormal:
		linkNode = NewNode(Link)
		linkNode.Destination = normalizeURI(uLink)
		linkNode.Title = title
		if len(altContent) > 0 {
			linkNode.AppendChild(text(altContent))

links cannot contain other links, so turn off link parsing temporarily and recurse

			insideLink := p.insideLink
			p.insideLink = true
			p.inline(linkNode, data[1:txtE])
			p.insideLink = insideLink
		}

	case linkImg:
		linkNode = NewNode(Image)
		linkNode.Destination = uLink
		linkNode.Title = title
		linkNode.AppendChild(text(data[1:txtE]))
		i++

	case linkInlineFootnote, linkDeferredFootnote:
		linkNode = NewNode(Link)
		linkNode.Destination = link
		linkNode.Title = title
		linkNode.NoteID = noteID
		linkNode.Footnote = footnoteNode
		if t == linkInlineFootnote {
			i++
		}

	default:
		return 0, nil
	}

	return i, linkNode
}

func (p *Markdown) inlineHTMLComment(data []byte) int {
	if len(data) < 5 {
		return 0
	}
	if data[0] != '<' || data[1] != '!' || data[2] != '-' || data[3] != '-' {
		return 0
	}

scan for an end-of-comment marker, across lines if necessary

	for i < len(data) && !(data[i-2] == '-' && data[i-1] == '-' && data[i] == '>') {
		i++

no end-of-comment marker

	if i >= len(data) {
		return 0
	}
	return i + 1
}

func stripMailto(link []byte) []byte {
	if bytes.HasPrefix(link, []byte("mailto://")) {
		return link[9:]
	} else if bytes.HasPrefix(link, []byte("mailto:")) {
		return link[7:]
	} else {
		return link
	}
}

autolinkType specifies a kind of autolink that gets detected.

type autolinkType int

These are the possible flag values for the autolink renderer.

const (
	notAutolink autolinkType = iota
	normalAutolink
	emailAutolink
)

'<' when tags or autolinks are allowed

func leftAngle(p *Markdown, data []byte, offset int) (int, *Node) {
	data = data[offset:]
	altype, end := tagLength(data)
	if size := p.inlineHTMLComment(data); size > 0 {
		end = size
	}
	if end > 2 {
		if altype != notAutolink {
			var uLink bytes.Buffer
			unescapeText(&uLink, data[1:end+1-2])
			if uLink.Len() > 0 {
				link := uLink.Bytes()
				node := NewNode(Link)
				node.Destination = link
				if altype == emailAutolink {
					node.Destination = append([]byte("mailto:"), link...)
				}
				node.AppendChild(text(stripMailto(link)))
				return end, node
			}
		} else {
			htmlTag := NewNode(HTMLSpan)
			htmlTag.Literal = data[:end]
			return end, htmlTag
		}
	}

	return end, nil
}

'\\' backslash escape

var escapeChars = []byte("\\`*_{}[]()#+-.!:|&<>~")

func escape(p *Markdown, data []byte, offset int) (int, *Node) {
	data = data[offset:]

	if len(data) > 1 {
		if p.extensions&BackslashLineBreak != 0 && data[1] == '\n' {
			return 2, NewNode(Hardbreak)
		}
		if bytes.IndexByte(escapeChars, data[1]) < 0 {
			return 0, nil
		}

		return 2, text(data[1:2])
	}

	return 2, nil
}

func unescapeText(ob *bytes.Buffer, src []byte) {
	i := 0
	for i < len(src) {
		org := i
		for i < len(src) && src[i] != '\\' {
			i++
		}

		if i > org {
			ob.Write(src[org:i])
		}

		if i+1 >= len(src) {
			break
		}

		ob.WriteByte(src[i+1])
		i += 2
	}
}

'&' escaped when it doesn't belong to an entity valid entities are assumed to be anything matching &#?[A-Za-z0-9]+;

func entity(p *Markdown, data []byte, offset int) (int, *Node) {
	data = data[offset:]

	end := 1

	if end < len(data) && data[end] == '#' {
		end++
	}

	for end < len(data) && isalnum(data[end]) {
		end++
	}

	if end < len(data) && data[end] == ';' {
		end++ // real entity
	} else {
		return 0, nil // lone '&'
	}

undo & escaping or it will be converted to &amp; by another escaper in the renderer

	if bytes.Equal(ent, []byte("&amp;")) {
		ent = []byte{'&'}
	}

	return end, text(ent)
}

func linkEndsWithEntity(data []byte, linkEnd int) bool {
	entityRanges := htmlEntityRe.FindAllIndex(data[:linkEnd], -1)
	return entityRanges != nil && entityRanges[len(entityRanges)-1][1] == linkEnd
}

hasPrefixCaseInsensitive is a custom implementation of strings.HasPrefix(strings.ToLower(s), prefix) we rolled our own because ToLower pulls in a huge machinery of lowercasing anything from Unicode and that's very slow. Since this func will only be used on ASCII protocol prefixes, we can take shortcuts.

func hasPrefixCaseInsensitive(s, prefix []byte) bool {
	if len(s) < len(prefix) {
		return false
	}
	delta := byte('a' - 'A')
	for i, b := range prefix {
		if b != s[i] && b != s[i]+delta {
			return false
		}
	}
	return true
}

var protocolPrefixes = [][]byte{
	[]byte("http://"),
	[]byte("https://"),
	[]byte("ftp://"),
	[]byte("file://"),
	[]byte("mailto:"),
}

const shortestPrefix = 6 // len("ftp://"), the shortest of the above

quick check to rule out most false hits

	if p.insideLink || len(data) < offset+shortestPrefix {
		return 0, nil
	}
	for _, prefix := range protocolPrefixes {
		endOfHead := offset + 8 // 8 is the len() of the longest prefix
		if endOfHead > len(data) {
			endOfHead = len(data)
		}
		if hasPrefixCaseInsensitive(data[offset:endOfHead], prefix) {
			return autoLink(p, data, offset)
		}
	}
	return 0, nil
}

Now a more expensive check to see if we're not inside an anchor element

	anchorStart := offset
	offsetFromAnchor := 0
	for anchorStart > 0 && data[anchorStart] != '<' {
		anchorStart--
		offsetFromAnchor++
	}

	anchorStr := anchorRe.Find(data[anchorStart:])
	if anchorStr != nil {
		anchorClose := NewNode(HTMLSpan)
		anchorClose.Literal = anchorStr[offsetFromAnchor:]
		return len(anchorStr) - offsetFromAnchor, anchorClose
	}

scan backward for a word boundary

	rewind := 0
	for offset-rewind > 0 && rewind <= 7 && isletter(data[offset-rewind-1]) {
		rewind++
	}
	if rewind > 6 { // longest supported protocol is "mailto" which has 6 letters
		return 0, nil
	}

	origData := data
	data = data[offset-rewind:]

	if !isSafeLink(data) {
		return 0, nil
	}

	linkEnd := 0
	for linkEnd < len(data) && !isEndOfLink(data[linkEnd]) {
		linkEnd++
	}

Skip punctuation at the end of the link

	if (data[linkEnd-1] == '.' || data[linkEnd-1] == ',') && data[linkEnd-2] != '\\' {
		linkEnd--
	}

But don't skip semicolon if it's a part of escaped entity:

	if data[linkEnd-1] == ';' && data[linkEnd-2] != '\\' && !linkEndsWithEntity(data, linkEnd) {
		linkEnd--
	}

See if the link finishes with a punctuation sign that can be closed.

	var copen byte
	switch data[linkEnd-1] {
	case '"':
		copen = '"'
	case '\'':
		copen = '\''
	case ')':
		copen = '('
	case ']':
		copen = '['
	case '}':
		copen = '{'
	default:
		copen = 0
	}

	if copen != 0 {
		bufEnd := offset - rewind + linkEnd - 2

		openDelim := 1

Try to close the final punctuation sign in this same line; * if we managed to close it outside of the URL, that means that it's * not part of the URL. If it closes inside the URL, that means it * is part of the URL. * * Examples: * * foo http:www.pokemon.com/Pikachu_(Electric) bar * => http:www.pokemon.com/Pikachu_(Electric) * * foo (http:www.pokemon.com/Pikachu_(Electric)) bar * => http:www.pokemon.com/Pikachu_(Electric) * * foo http:www.pokemon.com/Pikachu_(Electric)) bar * => http:www.pokemon.com/Pikachu_(Electric)) * * (foo http:www.pokemon.com/Pikachu_(Electric)) bar * => foo http:www.pokemon.com/Pikachu_(Electric)


		for bufEnd >= 0 && origData[bufEnd] != '\n' && openDelim != 0 {
			if origData[bufEnd] == data[linkEnd-1] {
				openDelim++
			}

			if origData[bufEnd] == copen {
				openDelim--
			}

			bufEnd--
		}

		if openDelim == 0 {
			linkEnd--
		}
	}

	var uLink bytes.Buffer
	unescapeText(&uLink, data[:linkEnd])

	if uLink.Len() > 0 {
		node := NewNode(Link)
		node.Destination = uLink.Bytes()
		node.AppendChild(text(uLink.Bytes()))
		return linkEnd, node
	}

	return linkEnd, nil
}

func isEndOfLink(char byte) bool {
	return isspace(char) || char == '<'
}

var validUris = [][]byte{[]byte("http://"), []byte("https://"), []byte("ftp://"), []byte("mailto://")}
var validPaths = [][]byte{[]byte("/"), []byte("./"), []byte("../")}

func isSafeLink(link []byte) bool {
	for _, path := range validPaths {
		if len(link) >= len(path) && bytes.Equal(link[:len(path)], path) {
			if len(link) == len(path) {
				return true
			} else if isalnum(link[len(path)]) {
				return true
			}
		}
	}

TODO: handle unicode here case-insensitive prefix test

		if len(link) > len(prefix) && bytes.Equal(bytes.ToLower(link[:len(prefix)]), prefix) && isalnum(link[len(prefix)]) {
			return true
		}
	}

	return false
}

return the length of the given tag, or 0 is it's not valid

func tagLength(data []byte) (autolink autolinkType, end int) {
	var i, j int

a valid tag can't be shorter than 3 chars

	if len(data) < 3 {
		return notAutolink, 0
	}

begins with a '<' optionally followed by '/', followed by letter or number

	if data[0] != '<' {
		return notAutolink, 0
	}
	if data[1] == '/' {
		i = 2
	} else {
		i = 1
	}

	if !isalnum(data[i]) {
		return notAutolink, 0
	}

scheme test

	autolink = notAutolink

try to find the beginning of an URI

	for i < len(data) && (isalnum(data[i]) || data[i] == '.' || data[i] == '+' || data[i] == '-') {
		i++
	}

	if i > 1 && i < len(data) && data[i] == '@' {
		if j = isMailtoAutoLink(data[i:]); j != 0 {
			return emailAutolink, i + j
		}
	}

	if i > 2 && i < len(data) && data[i] == ':' {
		autolink = normalAutolink
		i++
	}

complete autolink test: no whitespace or ' or "

	switch {
	case i >= len(data):
		autolink = notAutolink
	case autolink != notAutolink:
		j = i

		for i < len(data) {
			if data[i] == '\\' {
				i += 2
			} else if data[i] == '>' || data[i] == '\'' || data[i] == '"' || isspace(data[i]) {
				break
			} else {
				i++
			}

		}

		if i >= len(data) {
			return autolink, 0
		}
		if i > j && data[i] == '>' {
			return autolink, i + 1
		}

one of the forbidden chars has been found

		autolink = notAutolink
	}
	i += bytes.IndexByte(data[i:], '>')
	if i < 0 {
		return autolink, 0
	}
	return autolink, i + 1
}

look for the address part of a mail autolink and '>' this is less strict than the original markdown e-mail address matching

func isMailtoAutoLink(data []byte) int {
	nb := 0

address is assumed to be: [-@._a-zA-Z0-9]+ with exactly one '@'

	for i := 0; i < len(data); i++ {
		if isalnum(data[i]) {
			continue
		}

		switch data[i] {
		case '@':
			nb++

		case '-', '.', '_':
			break

		case '>':
			if nb == 1 {
				return i + 1
			}
			return 0
		default:
			return 0
		}
	}

	return 0
}

look for the next emph char, skipping other constructs

func helperFindEmphChar(data []byte, c byte) int {
	i := 0

	for i < len(data) {
		for i < len(data) && data[i] != c && data[i] != '`' && data[i] != '[' {
			i++
		}
		if i >= len(data) {
			return 0

do not count escaped chars

		if i != 0 && data[i-1] == '\\' {
			i++
			continue
		}
		if data[i] == c {
			return i
		}

skip a code span

			tmpI := 0
			i++
			for i < len(data) && data[i] != '`' {
				if tmpI == 0 && data[i] == c {
					tmpI = i
				}
				i++
			}
			if i >= len(data) {
				return tmpI
			}
			i++

skip a link

			tmpI := 0
			i++
			for i < len(data) && data[i] != ']' {
				if tmpI == 0 && data[i] == c {
					tmpI = i
				}
				i++
			}
			i++
			for i < len(data) && (data[i] == ' ' || data[i] == '\n') {
				i++
			}
			if i >= len(data) {
				return tmpI
			}
			if data[i] != '[' && data[i] != '(' { // not a link
				if tmpI > 0 {
					return tmpI
				}
				continue
			}
			cc := data[i]
			i++
			for i < len(data) && data[i] != cc {
				if tmpI == 0 && data[i] == c {
					return i
				}
				i++
			}
			if i >= len(data) {
				return tmpI
			}
			i++
		}
	}
	return 0
}

func helperEmphasis(p *Markdown, data []byte, c byte) (int, *Node) {
	i := 0

skip one symbol if coming from emph3

	if len(data) > 1 && data[0] == c && data[1] == c {
		i = 1
	}

	for i < len(data) {
		length := helperFindEmphChar(data[i:], c)
		if length == 0 {
			return 0, nil
		}
		i += length
		if i >= len(data) {
			return 0, nil
		}

		if i+1 < len(data) && data[i+1] == c {
			i++
			continue
		}

		if data[i] == c && !isspace(data[i-1]) {

			if p.extensions&NoIntraEmphasis != 0 {
				if !(i+1 == len(data) || isspace(data[i+1]) || ispunct(data[i+1])) {
					continue
				}
			}

			emph := NewNode(Emph)
			p.inline(emph, data[:i])
			return i + 1, emph
		}
	}

	return 0, nil
}

func helperDoubleEmphasis(p *Markdown, data []byte, c byte) (int, *Node) {
	i := 0

	for i < len(data) {
		length := helperFindEmphChar(data[i:], c)
		if length == 0 {
			return 0, nil
		}
		i += length

		if i+1 < len(data) && data[i] == c && data[i+1] == c && i > 0 && !isspace(data[i-1]) {
			nodeType := Strong
			if c == '~' {
				nodeType = Del
			}
			node := NewNode(nodeType)
			p.inline(node, data[:i])
			return i + 2, node
		}
		i++
	}
	return 0, nil
}

func helperTripleEmphasis(p *Markdown, data []byte, offset int, c byte) (int, *Node) {
	i := 0
	origData := data
	data = data[offset:]

	for i < len(data) {
		length := helperFindEmphChar(data[i:], c)
		if length == 0 {
			return 0, nil
		}
		i += length

skip whitespace preceded symbols

		if data[i] != c || isspace(data[i-1]) {
			continue
		}

		switch {

triple symbol found

			strong := NewNode(Strong)
			em := NewNode(Emph)
			strong.AppendChild(em)
			p.inline(em, data[:i])
			return i + 3, strong

double symbol found, hand over to emph1

			length, node := helperEmphasis(p, origData[offset-2:], c)
			if length == 0 {
				return 0, nil
			}
			return length - 2, node

single symbol found, hand over to emph2

			length, node := helperDoubleEmphasis(p, origData[offset-1:], c)
			if length == 0 {
				return 0, nil
			}
			return length - 1, node
		}
	}
	return 0, nil
}

func text(s []byte) *Node {
	node := NewNode(Text)
	node.Literal = s
	return node
}

func normalizeURI(s []byte) []byte {
	return s // TODO: implement