package parser

import (
	"bytes"
	"html"
	"regexp"
	"unicode"

	"github.com/gomarkdown/markdown/ast"
)

// Parsing block-level elements.

const (
	charEntity = "&(?:#x[a-f0-9]{1,8}|#[0-9]{1,8}|[a-z][a-z0-9]{1,31});"
	escapable  = "[!\"#$%&'()*+,./:;<=>?@[\\\\\\]^_`{|}~-]"
)

var (
	reBackslashOrAmp      = regexp.MustCompile("[\\&]")
	reEntityOrEscapedChar = regexp.MustCompile("(?i)\\\\" + escapable + "|" + charEntity)

	// blockTags is a set of tags that are recognized as HTML block tags.
	// Any of these can be included in markdown text without special escaping.
	blockTags = map[string]struct{}{
		"blockquote": struct{}{},
		"del":        struct{}{},
		"div":        struct{}{},
		"dl":         struct{}{},
		"fieldset":   struct{}{},
		"form":       struct{}{},
		"h1":         struct{}{},
		"h2":         struct{}{},
		"h3":         struct{}{},
		"h4":         struct{}{},
		"h5":         struct{}{},
		"h6":         struct{}{},
		"iframe":     struct{}{},
		"ins":        struct{}{},
		"math":       struct{}{},
		"noscript":   struct{}{},
		"ol":         struct{}{},
		"pre":        struct{}{},
		"p":          struct{}{},
		"script":     struct{}{},
		"style":      struct{}{},
		"table":      struct{}{},
		"ul":         struct{}{},

		// HTML5
		"address":    struct{}{},
		"article":    struct{}{},
		"aside":      struct{}{},
		"canvas":     struct{}{},
		"figcaption": struct{}{},
		"figure":     struct{}{},
		"footer":     struct{}{},
		"header":     struct{}{},
		"hgroup":     struct{}{},
		"main":       struct{}{},
		"nav":        struct{}{},
		"output":     struct{}{},
		"progress":   struct{}{},
		"section":    struct{}{},
		"video":      struct{}{},
	}
)

// sanitizeAnchorName returns a sanitized anchor name for the given text.
// Taken from https://github.com/shurcooL/sanitized_anchor_name/blob/master/main.go#L14:1
func sanitizeAnchorName(text string) string {
	var anchorName []rune
	var futureDash = false
	for _, r := range text {
		switch {
		case unicode.IsLetter(r) || unicode.IsNumber(r):
			if futureDash && len(anchorName) > 0 {
				anchorName = append(anchorName, '-')
			}
			futureDash = false
			anchorName = append(anchorName, unicode.ToLower(r))
		default:
			futureDash = true
		}
	}
	return string(anchorName)
}

// Parse block-level data.
// Note: this function and many that it calls assume that
// the input buffer ends with a newline.
func (p *Parser) block(data []byte) {
	// this is called recursively: enforce a maximum depth
	for len(data) > 0 {
		if i := p.fencedCodeBlock(data, true); i > 0 {
			data = data[i:]
			continue
		}

		if p.quotePrefix(data) > 0 {
			data = data[p.quote(data):]
			continue
		}

		idx := p.paragraph(data)
		data = data[idx:]
	}
	//p.renderParagraph(data)
	return

}

func (p *Parser) addBlock(n ast.Node) ast.Node {
	p.closeUnmatchedBlocks()

	if p.attr != nil {
		if c := n.AsContainer(); c != nil {
			c.Attribute = p.attr
		}
		if l := n.AsLeaf(); l != nil {
			l.Attribute = p.attr
		}
		p.attr = nil
	}
	return p.addChild(n)
}

func (p *Parser) isPrefixHeading(data []byte) bool {
	return len(data) > 1 && data[0] == '#' && isSpace(data[1])
}

func (p *Parser) prefixHeading(data []byte) int {
	level := skipCharN(data, 0, '#', 6)
	i := skipChar(data, level, ' ')
	end := skipUntilChar(data, i, '\n')
	skip := end
	for end > 0 && data[end-1] == '#' {
		if isBackslashEscaped(data, end-1) {
			break
		}
		end--
	}
	for end > 0 && data[end-1] == ' ' {
		end--
	}
	if end > i {
		block := &ast.Heading{
			Level: level,
		}
		block.Literal = data[i:end]
		p.addBlock(block)
	}
	return skip
}

func (p *Parser) isPrefixSpecialHeading(data []byte) bool {
	if len(data) < 4 {
		return false
	}
	if data[0] != '.' {
		return false
	}
	if data[1] != '#' {
		return false
	}
	if data[2] == '#' { // we don't support level, so nack this.
		return false
	}

	if p.extensions&SpaceHeadings != 0 {
		if data[2] != ' ' {
			return false
		}
	}
	return true
}

func (p *Parser) prefixSpecialHeading(data []byte) int {
	i := skipChar(data, 2, ' ') // ".#" skipped
	end := skipUntilChar(data, i, '\n')
	skip := end
	id := ""
	if p.extensions&HeadingIDs != 0 {
		j, k := 0, 0
		// find start/end of heading id
		for j = i; j < end-1 && (data[j] != '{' || data[j+1] != '#'); j++ {
		}
		for k = j + 1; k < end && data[k] != '}'; k++ {
		}
		// extract heading id iff found
		if j < end && k < end {
			id = string(data[j+2 : k])
			end = j
			skip = k + 1
			for end > 0 && data[end-1] == ' ' {
				end--
			}
		}
	}
	for end > 0 && data[end-1] == '#' {
		if isBackslashEscaped(data, end-1) {
			break
		}
		end--
	}
	for end > 0 && data[end-1] == ' ' {
		end--
	}
	if end > i {
		if id == "" && p.extensions&AutoHeadingIDs != 0 {
			id = sanitizeAnchorName(string(data[i:end]))
		}
		block := &ast.Heading{
			HeadingID: id,
			IsSpecial: true,
			Level:     1, // always level 1.
		}
		block.Literal = data[i:end]
		block.Content = data[i:end]
		p.addBlock(block)
	}
	return skip
}

func (p *Parser) isUnderlinedHeading(data []byte) int {
	// test of level 1 heading
	if data[0] == '=' {
		i := skipChar(data, 1, '=')
		i = skipChar(data, i, ' ')
		if i < len(data) && data[i] == '\n' {
			return 1
		}
		return 0
	}

	// test of level 2 heading
	if data[0] == '-' {
		i := skipChar(data, 1, '-')
		i = skipChar(data, i, ' ')
		if i < len(data) && data[i] == '\n' {
			return 2
		}
		return 0
	}

	return 0
}

func (p *Parser) titleBlock(data []byte, doRender bool) int {
	if data[0] != '%' {
		return 0
	}
	splitData := bytes.Split(data, []byte("\n"))
	var i int
	for idx, b := range splitData {
		if !bytes.HasPrefix(b, []byte("%")) {
			i = idx // - 1
			break
		}
	}

	data = bytes.Join(splitData[0:i], []byte("\n"))
	consumed := len(data)
	data = bytes.TrimPrefix(data, []byte("% "))
	data = bytes.Replace(data, []byte("\n% "), []byte("\n"), -1)
	block := &ast.Heading{
		Level:        1,
		IsTitleblock: true,
	}
	block.Content = data
	p.addBlock(block)

	return consumed
}

func (*Parser) isEmpty(data []byte) int {
	// it is okay to call isEmpty on an empty buffer
	if len(data) == 0 {
		return 0
	}

	var i int
	for i = 0; i < len(data) && data[i] != '\n'; i++ {
		if data[i] != ' ' && data[i] != '\t' {
			return 0
		}
	}
	i = skipCharN(data, i, '\n', 1)
	return i
}

func (*Parser) isHRule(data []byte) bool {
	i := 0

	// skip up to three spaces
	for i < 3 && data[i] == ' ' {
		i++
	}

	// look at the hrule char
	if data[i] != '*' && data[i] != '-' && data[i] != '_' {
		return false
	}
	c := data[i]

	// the whole line must be the char or whitespace
	n := 0
	for i < len(data) && data[i] != '\n' {
		switch {
		case data[i] == c:
			n++
		case data[i] != ' ':
			return false
		}
		i++
	}

	return n >= 3
}

// isFenceLine checks if there's a fence line (e.g., ``` or ``` go) at the beginning of data,
// and returns the end index if so, or 0 otherwise. It also returns the marker found.
// If syntax is not nil, it gets set to the syntax specified in the fence line.
func isFenceLine(data []byte, syntax *string, oldmarker string) (end int, marker string) {
	i, size := 0, 0

	n := len(data)
	// skip up to three spaces
	for i < n && i < 3 && data[i] == ' ' {
		i++
	}

	// check for the marker characters: ~ or `
	if i >= n {
		return 0, ""
	}
	if data[i] != '~' && data[i] != '`' {
		return 0, ""
	}

	c := data[i]

	// the whole line must be the same char or whitespace
	for i < n && data[i] == c {
		size++
		i++
	}

	// the marker char must occur at least 3 times
	if size < 3 {
		return 0, ""
	}
	marker = string(data[i-size : i])

	// if this is the end marker, it must match the beginning marker
	if oldmarker != "" && marker != oldmarker {
		return 0, ""
	}

	// TODO(shurcooL): It's probably a good idea to simplify the 2 code paths here
	// into one, always get the syntax, and discard it if the caller doesn't care.
	if syntax != nil {
		syn := 0
		i = skipChar(data, i, ' ')

		if i >= n {
			if i == n {
				return i, marker
			}
			return 0, ""
		}

		syntaxStart := i

		if data[i] == '{' {
			i++
			syntaxStart++

			for i < n && data[i] != '}' && data[i] != '\n' {
				syn++
				i++
			}

			if i >= n || data[i] != '}' {
				return 0, ""
			}

			// strip all whitespace at the beginning and the end
			// of the {} block
			for syn > 0 && isSpace(data[syntaxStart]) {
				syntaxStart++
				syn--
			}

			for syn > 0 && isSpace(data[syntaxStart+syn-1]) {
				syn--
			}

			i++
		} else {
			for i < n && !isSpace(data[i]) {
				syn++
				i++
			}
		}

		*syntax = string(data[syntaxStart : syntaxStart+syn])
	}

	i = skipChar(data, i, ' ')
	if i >= n || data[i] != '\n' {
		if i == n {
			return i, marker
		}
		return 0, ""
	}
	return i + 1, marker // Take newline into account.
}

// fencedCodeBlock returns the end index if data contains a fenced code block at the beginning,
// or 0 otherwise. It writes to out if doRender is true, otherwise it has no side effects.
// If doRender is true, a final newline is mandatory to recognize the fenced code block.
func (p *Parser) fencedCodeBlock(data []byte, doRender bool) int {
	var syntax string
	beg, marker := isFenceLine(data, &syntax, "")
	if beg == 0 || beg >= len(data) {
		return 0
	}

	var work bytes.Buffer
	work.WriteString(syntax)
	work.WriteByte('\n')

	for {
		// safe to assume beg < len(data)

		// check for the end of the code block
		fenceEnd, _ := isFenceLine(data[beg:], nil, marker)
		if fenceEnd != 0 {
			beg += fenceEnd
			break
		}

		// copy the current line
		end := skipUntilChar(data, beg, '\n') + 1

		// did we reach the end of the buffer without a closing marker?
		if end >= len(data) {
			return 0
		}

		// verbatim copy to the working buffer
		if doRender {
			work.Write(data[beg:end])
		}
		beg = end
	}

	if doRender {
		codeBlock := &ast.CodeBlock{
			IsFenced: true,
		}
		codeBlock.Content = work.Bytes() // TODO: get rid of temp buffer

		// Check for caption and if found make it a figure.
		if captionContent, id, consumed := p.caption(data[beg:], []byte("Figure: ")); consumed > 0 {
			figure := &ast.CaptionFigure{}
			caption := &ast.Caption{}
			figure.HeadingID = id
			p.Inline(caption, captionContent)

			p.addBlock(figure)
			codeBlock.AsLeaf().Attribute = figure.AsContainer().Attribute
			p.addChild(codeBlock)
			finalizeCodeBlock(codeBlock)
			p.addChild(caption)
			p.finalize(figure)

			beg += consumed

			return beg
		}

		// Still here, normal block
		p.addBlock(codeBlock)
		finalizeCodeBlock(codeBlock)
	}

	return beg
}

func unescapeChar(str []byte) []byte {
	if str[0] == '\\' {
		return []byte{str[1]}
	}
	return []byte(html.UnescapeString(string(str)))
}

func unescapeString(str []byte) []byte {
	if reBackslashOrAmp.Match(str) {
		return reEntityOrEscapedChar.ReplaceAllFunc(str, unescapeChar)
	}
	return str
}

func finalizeCodeBlock(code *ast.CodeBlock) {
	c := code.Content
	if code.IsFenced {
		newlinePos := bytes.IndexByte(c, '\n')
		firstLine := c[:newlinePos]
		rest := c[newlinePos+1:]
		code.Info = unescapeString(bytes.Trim(firstLine, "\n"))
		code.Literal = rest
	} else {
		code.Literal = c
	}
	code.Content = nil
}

func (p *Parser) table(data []byte) int {
	i, columns, table := p.tableHeader(data)
	if i == 0 {
		return 0
	}

	p.addBlock(&ast.TableBody{})

	for i < len(data) {
		pipes, rowStart := 0, i
		for ; i < len(data) && data[i] != '\n'; i++ {
			if data[i] == '|' {
				pipes++
			}
		}

		if pipes == 0 {
			i = rowStart
			break
		}

		// include the newline in data sent to tableRow
		i = skipCharN(data, i, '\n', 1)

		if p.tableFooter(data[rowStart:i]) {
			continue
		}

		p.tableRow(data[rowStart:i], columns, false)
	}
	if captionContent, id, consumed := p.caption(data[i:], []byte("Table: ")); consumed > 0 {
		caption := &ast.Caption{}
		p.Inline(caption, captionContent)

		// Some switcheroo to re-insert the parsed table as a child of the captionfigure.
		figure := &ast.CaptionFigure{}
		figure.HeadingID = id
		table2 := &ast.Table{}
		// Retain any block level attributes.
		table2.AsContainer().Attribute = table.AsContainer().Attribute
		children := table.GetChildren()
		ast.RemoveFromTree(table)

		table2.SetChildren(children)
		ast.AppendChild(figure, table2)
		ast.AppendChild(figure, caption)

		p.addChild(figure)
		p.finalize(figure)

		i += consumed
	}

	return i
}

// check if the specified position is preceded by an odd number of backslashes
func isBackslashEscaped(data []byte, i int) bool {
	backslashes := 0
	for i-backslashes-1 >= 0 && data[i-backslashes-1] == '\\' {
		backslashes++
	}
	return backslashes&1 == 1
}

// tableHeaders parses the header. If recognized it will also add a table.
func (p *Parser) tableHeader(data []byte) (size int, columns []ast.CellAlignFlags, table ast.Node) {
	i := 0
	colCount := 1
	for i = 0; i < len(data) && data[i] != '\n'; i++ {
		if data[i] == '|' && !isBackslashEscaped(data, i) {
			colCount++
		}
	}

	// doesn't look like a table header
	if colCount == 1 {
		return
	}

	// include the newline in the data sent to tableRow
	j := skipCharN(data, i, '\n', 1)
	header := data[:j]

	// column count ignores pipes at beginning or end of line
	if data[0] == '|' {
		colCount--
	}
	if i > 2 && data[i-1] == '|' && !isBackslashEscaped(data, i-1) {
		colCount--
	}

	columns = make([]ast.CellAlignFlags, colCount)

	// move on to the header underline
	i++
	if i >= len(data) {
		return
	}

	if data[i] == '|' && !isBackslashEscaped(data, i) {
		i++
	}
	i = skipChar(data, i, ' ')

	// each column header is of form: / *:?-+:? *|/ with # dashes + # colons >= 3
	// and trailing | optional on last column
	col := 0
	n := len(data)
	for i < n && data[i] != '\n' {
		dashes := 0

		if data[i] == ':' {
			i++
			columns[col] |= ast.TableAlignmentLeft
			dashes++
		}
		for i < n && data[i] == '-' {
			i++
			dashes++
		}
		if i < n && data[i] == ':' {
			i++
			columns[col] |= ast.TableAlignmentRight
			dashes++
		}
		for i < n && data[i] == ' ' {
			i++
		}
		if i == n {
			return
		}
		// end of column test is messy
		switch {
		case dashes < 3:
			// not a valid column
			return

		case data[i] == '|' && !isBackslashEscaped(data, i):
			// marker found, now skip past trailing whitespace
			col++
			i++
			for i < n && data[i] == ' ' {
				i++
			}

			// trailing junk found after last column
			if col >= colCount && i < len(data) && data[i] != '\n' {
				return
			}

		case (data[i] != '|' || isBackslashEscaped(data, i)) && col+1 < colCount:
			// something else found where marker was required
			return

		case data[i] == '\n':
			// marker is optional for the last column
			col++

		default:
			// trailing junk found after last column
			return
		}
	}
	if col != colCount {
		return
	}

	table = &ast.Table{}
	p.addBlock(table)
	p.addBlock(&ast.TableHeader{})
	p.tableRow(header, columns, true)
	size = skipCharN(data, i, '\n', 1)
	return
}

func (p *Parser) tableRow(data []byte, columns []ast.CellAlignFlags, header bool) {
	p.addBlock(&ast.TableRow{})
	i, col := 0, 0

	if data[i] == '|' && !isBackslashEscaped(data, i) {
		i++
	}

	n := len(data)
	for col = 0; col < len(columns) && i < n; col++ {
		for i < n && data[i] == ' ' {
			i++
		}

		cellStart := i

		for i < n && (data[i] != '|' || isBackslashEscaped(data, i)) && data[i] != '\n' {
			i++
		}

		cellEnd := i

		// skip the end-of-cell marker, possibly taking us past end of buffer
		i++

		for cellEnd > cellStart && cellEnd-1 < n && data[cellEnd-1] == ' ' {
			cellEnd--
		}

		block := &ast.TableCell{
			IsHeader: header,
			Align:    columns[col],
		}
		block.Content = data[cellStart:cellEnd]
		p.addBlock(block)
	}

	// pad it out with empty columns to get the right number
	for ; col < len(columns); col++ {
		block := &ast.TableCell{
			IsHeader: header,
			Align:    columns[col],
		}
		p.addBlock(block)
	}

	// silently ignore rows with too many cells
}

// tableFooter parses the (optional) table footer.
func (p *Parser) tableFooter(data []byte) bool {
	colCount := 1
	for i := 0; i < len(data) && data[i] != '\n'; i++ {
		if data[i] == '|' && !isBackslashEscaped(data, i) {
			colCount++
			continue
		}
		// remaining data must be the = character
		if data[i] != '=' {
			return false
		}
	}

	// doesn't look like a table footer
	if colCount == 1 {
		return false
	}

	p.addBlock(&ast.TableFooter{})

	return true
}

// returns blockquote prefix length
func (p *Parser) quotePrefix(data []byte) int {
	i := 0
	n := len(data)
	for i < 3 && i < n && data[i] == ' ' {
		i++
	}
	if i < n && data[i] == '>' {
		if i+1 < n && data[i+1] == ' ' {
			return i + 2
		}
		return i + 1
	}
	return 0
}

// blockquote ends with at least one blank line
// followed by something without a blockquote prefix
func (p *Parser) terminateBlockquote(data []byte, beg, end int) bool {
	if p.isEmpty(data[beg:]) <= 0 {
		return false
	}
	if end >= len(data) {
		return true
	}
	return p.quotePrefix(data[end:]) == 0 && p.isEmpty(data[end:]) == 0
}

// parse a blockquote fragment
func (p *Parser) quote(data []byte) int {
	var raw bytes.Buffer
	beg, end := 0, 0
	for beg < len(data) {
		end = beg
		// Step over whole lines, collecting them. While doing that, check for
		// fenced code and if one's found, incorporate it altogether,
		// irregardless of any contents inside it
		for end < len(data) && data[end] != '\n' {
			end++
		}
		end = skipCharN(data, end, '\n', 1)
		if pre := p.quotePrefix(data[beg:]); pre > 0 {
			// skip the prefix
			beg += pre
		} else if p.terminateBlockquote(data, beg, end) {
			break
		}
		// this line is part of the blockquote
		raw.Write(data[beg:end])
		beg = end
	}

	quote := &ast.BlockQuote{}
	quote.Literal = raw.Bytes()
	block := p.addBlock(quote)
	p.finalize(block)

	return end
}

// returns prefix length for block code
func (p *Parser) codePrefix(data []byte) int {
	n := len(data)
	if n >= 1 && data[0] == '\t' {
		return 1
	}
	if n >= 4 && data[3] == ' ' && data[2] == ' ' && data[1] == ' ' && data[0] == ' ' {
		return 4
	}
	return 0
}

func (p *Parser) code(data []byte) int {
	var work bytes.Buffer

	i := 0
	for i < len(data) {
		beg := i

		i = skipUntilChar(data, i, '\n')
		i = skipCharN(data, i, '\n', 1)

		blankline := p.isEmpty(data[beg:i]) > 0
		if pre := p.codePrefix(data[beg:i]); pre > 0 {
			beg += pre
		} else if !blankline {
			// non-empty, non-prefixed line breaks the pre
			i = beg
			break
		}

		// verbatim copy to the working buffer
		if blankline {
			work.WriteByte('\n')
		} else {
			work.Write(data[beg:i])
		}
	}

	// trim all the \n off the end of work
	workbytes := work.Bytes()

	eol := backChar(workbytes, len(workbytes), '\n')

	if eol != len(workbytes) {
		work.Truncate(eol)
	}

	work.WriteByte('\n')

	codeBlock := &ast.CodeBlock{
		IsFenced: false,
	}
	// TODO: get rid of temp buffer
	codeBlock.Content = work.Bytes()
	p.addBlock(codeBlock)
	finalizeCodeBlock(codeBlock)

	return i
}

// returns unordered list item prefix
func (p *Parser) uliPrefix(data []byte) int {
	// start with up to 3 spaces
	i := skipCharN(data, 0, ' ', 3)

	if i >= len(data)-1 {
		return 0
	}
	// need one of {'*', '+', '-'} followed by a space or a tab
	if (data[i] != '*' && data[i] != '+' && data[i] != '-') ||
		(data[i+1] != ' ' && data[i+1] != '\t') {
		return 0
	}
	return i + 2
}

// returns ordered list item prefix
func (p *Parser) oliPrefix(data []byte) int {
	// start with up to 3 spaces
	i := skipCharN(data, 0, ' ', 3)

	// count the digits
	start := i
	for i < len(data) && data[i] >= '0' && data[i] <= '9' {
		i++
	}
	if start == i || i >= len(data)-1 {
		return 0
	}

	// we need >= 1 digits followed by a dot and a space or a tab
	if data[i] != '.' || !(data[i+1] == ' ' || data[i+1] == '\t') {
		return 0
	}
	return i + 2
}

// returns definition list item prefix
func (p *Parser) dliPrefix(data []byte) int {
	if len(data) < 2 {
		return 0
	}
	// need a ':' followed by a space or a tab
	if data[0] != ':' || !(data[1] == ' ' || data[1] == '\t') {
		return 0
	}
	i := skipChar(data, 0, ' ')
	return i + 2
}

// parse ordered or unordered list block
func (p *Parser) list(data []byte, flags ast.ListType, start int) int {
	i := 0
	flags |= ast.ListItemBeginningOfList
	list := &ast.List{
		ListFlags: flags,
		Tight:     true,
		Start:     start,
	}
	block := p.addBlock(list)

	for i < len(data) {
		skip := p.listItem(data[i:], &flags)
		if flags&ast.ListItemContainsBlock != 0 {
			list.Tight = false
		}
		i += skip
		if skip == 0 || flags&ast.ListItemEndOfList != 0 {
			break
		}
		flags &= ^ast.ListItemBeginningOfList
	}

	above := block.GetParent()
	finalizeList(list)
	p.tip = above
	return i
}

// Returns true if the list item is not the same type as its parent list
func (p *Parser) listTypeChanged(data []byte, flags *ast.ListType) bool {
	if p.dliPrefix(data) > 0 && *flags&ast.ListTypeDefinition == 0 {
		return true
	} else if p.oliPrefix(data) > 0 && *flags&ast.ListTypeOrdered == 0 {
		return true
	} else if p.uliPrefix(data) > 0 && (*flags&ast.ListTypeOrdered != 0 || *flags&ast.ListTypeDefinition != 0) {
		return true
	}
	return false
}

// Returns true if block ends with a blank line, descending if needed
// into lists and sublists.
func endsWithBlankLine(block ast.Node) bool {
	// TODO: figure this out. Always false now.
	for block != nil {
		//if block.lastLineBlank {
		//return true
		//}
		switch block.(type) {
		case *ast.List, *ast.ListItem:
			block = ast.GetLastChild(block)
		default:
			return false
		}
	}
	return false
}

func finalizeList(list *ast.List) {
	items := list.Parent.GetChildren()
	lastItemIdx := len(items) - 1
	for i, item := range items {
		isLastItem := i == lastItemIdx
		// check for non-final list item ending with blank line:
		if !isLastItem && endsWithBlankLine(item) {
			list.Tight = false
			break
		}
		// recurse into children of list item, to see if there are spaces
		// between any of them:
		subItems := item.GetParent().GetChildren()
		lastSubItemIdx := len(subItems) - 1
		for j, subItem := range subItems {
			isLastSubItem := j == lastSubItemIdx
			if (!isLastItem || !isLastSubItem) && endsWithBlankLine(subItem) {
				list.Tight = false
				break
			}
		}
	}
}

// Parse a single list item.
// Assumes initial prefix is already removed if this is a sublist.
func (p *Parser) listItem(data []byte, flags *ast.ListType) int {
	// keep track of the indentation of the first line
	itemIndent := 0
	if data[0] == '\t' {
		itemIndent += 4
	} else {
		for itemIndent < 3 && data[itemIndent] == ' ' {
			itemIndent++
		}
	}

	var bulletChar byte = '*'
	i := p.uliPrefix(data)
	if i == 0 {
		i = p.oliPrefix(data)
	} else {
		bulletChar = data[i-2]
	}
	if i == 0 {
		i = p.dliPrefix(data)
		// reset definition term flag
		if i > 0 {
			*flags &= ^ast.ListTypeTerm
		}
	}
	if i == 0 {
		// if in definition list, set term flag and continue
		if *flags&ast.ListTypeDefinition != 0 {
			*flags |= ast.ListTypeTerm
		} else {
			return 0
		}
	}

	// skip leading whitespace on first line
	i = skipChar(data, i, ' ')

	// find the end of the line
	line := i
	for i > 0 && i < len(data) && data[i-1] != '\n' {
		i++
	}

	// get working buffer
	var raw bytes.Buffer

	// put the first line into the working buffer
	raw.Write(data[line:i])
	line = i

	// process the following lines
	containsBlankLine := false
	sublist := 0

gatherlines:
	for line < len(data) {
		i++

		// find the end of this line
		for i < len(data) && data[i-1] != '\n' {
			i++
		}

		// if it is an empty line, guess that it is part of this item
		// and move on to the next line
		if p.isEmpty(data[line:i]) > 0 {
			containsBlankLine = true
			line = i
			continue
		}

		// calculate the indentation
		indent := 0
		indentIndex := 0
		if data[line] == '\t' {
			indentIndex++
			indent += 4
		} else {
			for indent < 4 && line+indent < i && data[line+indent] == ' ' {
				indent++
				indentIndex++
			}
		}

		chunk := data[line+indentIndex : i]

		// evaluate how this line fits in
		switch {
		// is this a nested list item?
		case (p.uliPrefix(chunk) > 0 && !p.isHRule(chunk)) || p.oliPrefix(chunk) > 0 || p.dliPrefix(chunk) > 0:

			// to be a nested list, it must be indented more
			// if not, it is either a different kind of list
			// or the next item in the same list
			if indent <= itemIndent {
				if p.listTypeChanged(chunk, flags) {
					*flags |= ast.ListItemEndOfList
				} else if containsBlankLine {
					*flags |= ast.ListItemContainsBlock
				}

				break gatherlines
			}

			if containsBlankLine {
				*flags |= ast.ListItemContainsBlock
			}

			// is this the first item in the nested list?
			if sublist == 0 {
				sublist = raw.Len()
				// in the case of dliPrefix we are too late and need to search back for the definition item, which
				// should be on the previous line, we then adjust sublist to start there.
				if p.dliPrefix(chunk) > 0 {
					sublist = backUntilChar(raw.Bytes(), raw.Len()-1, '\n')
				}
			}

			// is this a nested prefix heading?
		case p.isPrefixHeading(chunk), p.isPrefixSpecialHeading(chunk):
			// if the heading is not indented, it is not nested in the list
			// and thus ends the list
			if containsBlankLine && indent < 4 {
				*flags |= ast.ListItemEndOfList
				break gatherlines
			}
			*flags |= ast.ListItemContainsBlock

		// anything following an empty line is only part
		// of this item if it is indented 4 spaces
		// (regardless of the indentation of the beginning of the item)
		case containsBlankLine && indent < 4:
			if *flags&ast.ListTypeDefinition != 0 && i < len(data)-1 {
				// is the next item still a part of this list?
				next := i
				for next < len(data) && data[next] != '\n' {
					next++
				}
				for next < len(data)-1 && data[next] == '\n' {
					next++
				}
				if i < len(data)-1 && data[i] != ':' && next < len(data)-1 && data[next] != ':' {
					*flags |= ast.ListItemEndOfList
				}
			} else {
				*flags |= ast.ListItemEndOfList
			}
			break gatherlines

		// a blank line means this should be parsed as a block
		case containsBlankLine:
			raw.WriteByte('\n')
			*flags |= ast.ListItemContainsBlock
		}

		// if this line was preceded by one or more blanks,
		// re-introduce the blank into the buffer
		if containsBlankLine {
			containsBlankLine = false
			raw.WriteByte('\n')
		}

		// add the line into the working buffer without prefix
		raw.Write(data[line+indentIndex : i])

		line = i
	}

	rawBytes := raw.Bytes()

	listItem := &ast.ListItem{
		ListFlags:  *flags,
		Tight:      false,
		BulletChar: bulletChar,
		Delimiter:  '.', // Only '.' is possible in Markdown, but ')' will also be possible in CommonMark
	}
	p.addBlock(listItem)

	// render the contents of the list item
	if *flags&ast.ListItemContainsBlock != 0 && *flags&ast.ListTypeTerm == 0 {
		// intermediate render of block item, except for definition term
		if sublist > 0 {
			p.block(rawBytes[:sublist])
			p.block(rawBytes[sublist:])
		} else {
			p.block(rawBytes)
		}
	} else {
		// intermediate render of inline item
		para := &ast.Paragraph{}
		if sublist > 0 {
			para.Content = rawBytes[:sublist]
		} else {
			para.Content = rawBytes
		}
		p.addChild(para)
		if sublist > 0 {
			p.block(rawBytes[sublist:])
		}
	}
	return line
}

// render a single paragraph that has already been parsed out
func (p *Parser) renderParagraph(data []byte) {
	if len(data) == 0 {
		return
	}

	// trim leading spaces
	beg := skipChar(data, 0, ' ')

	end := len(data)
	// trim trailing newline
	if data[len(data)-1] == '\n' {
		end--
	}

	// trim trailing spaces
	for end > beg && data[end-1] == ' ' {
		end--
	}
	para := &ast.Paragraph{}
	para.Content = data[beg:end]
	p.addBlock(para)
}

// blockMath handle block surround with $$
func (p *Parser) blockMath(data []byte) int {
	if len(data) <= 4 || data[0] != '$' || data[1] != '$' || data[2] == '$' {
		return 0
	}

	// find next $$
	var end int
	for end = 2; end+1 < len(data) && (data[end] != '$' || data[end+1] != '$'); end++ {
	}

	// $$ not match
	if end+1 == len(data) {
		return 0
	}

	// render the display math
	mathBlock := &ast.MathBlock{}
	mathBlock.Literal = data[2:end]
	p.addBlock(mathBlock)

	return end + 2
}

func (p *Parser) paragraph(data []byte) int {
	// prev: index of 1st char of previous line
	// line: index of 1st char of current line
	// i: index of cursor/end of current line
	var prev, line, i int
	tabSize := tabSizeDefault
	if p.extensions&TabSizeEight != 0 {
		tabSize = tabSizeDouble
	}
	// keep going until we find something to mark the end of the paragraph
	for i < len(data) {
		// mark the beginning of the current line
		prev = line
		current := data[i:]
		line = i

		// did we find a reference or a footnote? If so, end a paragraph
		// preceding it and report that we have consumed up to the end of that
		// reference:
		if refEnd := isReference(p, current, tabSize); refEnd > 0 {
			p.renderParagraph(data[:i])
			return i + refEnd
		}

		// did we find a blank line marking the end of the paragraph?
		if n := p.isEmpty(current); n > 0 {
			p.renderParagraph(data[:i])
			return i + n
		}

		// an underline under some text marks a heading, so our paragraph ended on prev line
		if i > 0 {
			if level := p.isUnderlinedHeading(current); level > 0 {
				// render the paragraph
				p.renderParagraph(data[:prev])

				// ignore leading and trailing whitespace
				eol := i - 1
				for prev < eol && data[prev] == ' ' {
					prev++
				}
				for eol > prev && data[eol-1] == ' ' {
					eol--
				}

				id := ""
				if p.extensions&AutoHeadingIDs != 0 {
					id = sanitizeAnchorName(string(data[prev:eol]))
				}

				block := &ast.Heading{
					Level:     level,
					HeadingID: id,
				}
				block.Content = data[prev:eol]
				p.addBlock(block)

				// find the end of the underline
				return skipUntilChar(data, i, '\n')
			}
		}

		// if there's a fenced code block, paragraph is over
		if p.extensions&FencedCode != 0 {
			if p.fencedCodeBlock(current, false) > 0 {
				p.renderParagraph(data[:i])
				return i
			}
		}

		// otherwise, scan to the beginning of the next line
		nl := bytes.IndexByte(data[i:], '\n')
		if nl >= 0 {
			i += nl + 1
		} else {
			i += len(data[i:])
		}
	}

	p.renderParagraph(data[:i])
	return i
}

// skipChar advances i as long as data[i] == c
func skipChar(data []byte, i int, c byte) int {
	n := len(data)
	for i < n && data[i] == c {
		i++
	}
	return i
}

// like skipChar but only skips up to max characters
func skipCharN(data []byte, i int, c byte, max int) int {
	n := len(data)
	for i < n && max > 0 && data[i] == c {
		i++
		max--
	}
	return i
}

// skipUntilChar advances i as long as data[i] != c
func skipUntilChar(data []byte, i int, c byte) int {
	n := len(data)
	for i < n && data[i] != c {
		i++
	}
	return i
}

func skipAlnum(data []byte, i int) int {
	n := len(data)
	for i < n && isAlnum(data[i]) {
		i++
	}
	return i
}

func skipSpace(data []byte, i int) int {
	n := len(data)
	for i < n && isSpace(data[i]) {
		i++
	}
	return i
}

func backChar(data []byte, i int, c byte) int {
	for i > 0 && data[i-1] == c {
		i--
	}
	return i
}

func backUntilChar(data []byte, i int, c byte) int {
	for i > 0 && data[i-1] != c {
		i--
	}
	return i
}